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# Mechanical Testing - Science topic

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Questions related to Mechanical Testing
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Hello fellow researchers,
I would like to measure strain using an LVDT for tensile testing for a specific test.
If any of you have hands-on experience with interfacing an LVDT to an MTS flextest controller, I'd greatly appreciate your insights and advice.with
Thanks
Hi Junxian Chen , from your experience is it chatGPT or Google Bard providing better replies to scientific questions?
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I have results from a load-deflection curve that behaves non-linearly. I need to convert this to a stress-strain curve and/or find the final Modulus of Rupture (MOR).
To do so, converting the deflection into strain is possible as per ASTM D790
εf = 6Dd/L^2, where D is the maximum deflection, d is depth and L is the span length.
I would like to convert the load to stress as well, however, the conventional equation from beam theory is not applicable past the yield point,
σf = 3PL/2bd^2, where P is the load.
I'm aware that it somehow involves the neutral axis and the modified I (moment of inertia) but struggling to make sense of it. The end goal is to find the MOR.
In my opinion, to reconstruct σ-ε diagram from known load-deflection curve is a kind of inverse problem. Generally speaking, such problems are ill posed. You can proceed from some particular approximation of σ-ε diagram (for example, bilinear), find the solution of direct problem (load-deflection curve) and then vary the parameters of σ-ε diagram to find those that give a minimum deviation (eg, the mean square) of load-deflection curve from the experimental one.
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Currently, I learn the mechanism of plastic mechanical testing related to the analytical mechanics in Physics field. The testing conducted are Tensile, Flexural and Impact test that resulting in Tension, compression and propagation mechanism. Besides, mechanical testing also shows fracture, displacement and strain phenomena that can be described using analytical mechanics. Thus, can anyone suggest any references related to those topics?
Thank you in advance,
Asep Bustanil Aripin
1. "Mechanics of Materials" by Ferdinand P. Beer, E. Russell Johnston Jr., and John T. DeWolf
2. "Introduction to the Mechanics of Solids" by Stephen H. Crandall
3. "Mechanical Behavior of Materials" by Norman E. Dowling
4. "Fracture Mechanics: Fundamentals and Applications" by T.L. Anderson
5. "Mechanics of Materials: An Integrated Learning System" by Timothy A. Philpot
These are just a few examples of textbooks that cover analytical solutions in mechanics for plastic mechanical testing. You can also find many research papers and articles on this topic by searching academic databases like Google Scholar or Scopus.
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I intend to perform mechanical tensile test for my polymer nanocomposites. Does there exists any ASTM standard to follow? Can I also know the dimensions of the specimen to be produced? Lastly, I intend to create a mould for the dog-bone shape. Can we get files online to create the dog-bone mould using 3D printer?
Yes, there are several ASTM standards available for performing mechanical tensile tests on polymer nanocomposites. Some of the commonly used standards are:
1. ASTM D638 - Standard Test Method for Tensile Properties of Plastics
2. ASTM D3039 - Standard Test Method for Tensile Properties of Polymer Matrix Composite Materials
3. ASTM D882 - Standard Test Method for Tensile Properties of Thin Plastic Sheeting
The dimensions of the specimen depend on the specific ASTM standard chosen for the test. For example, ASTM D638 specifies the dimensions for Type I, II and III specimens. Similarly, ASTM D3039 and ASTM D882 specify the dimensions for different types of specimens.
Regarding the creation of a dog-bone mold using a 3D printer, there are several online resources available that provide files for 3D printing dog-bone molds. Some popular online resources include Thingiverse, GrabCAD, and MyMiniFactory. However, it is important to ensure that the dimensions of the mold are as per the ASTM standards to obtain accurate results.
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Hi,
I'm conducting compressive mechanical tests on jello material on a rheometer HR20 by TA Instruments. The cross hatched top plate is 8mm in diameter and circular in shape.
I'm testing hockey puck shaped jello samples ( 8mm in diameter, 2mm in height) and calculated the area under the curve given by the software.
1. I'm getting results as Pa %. Don't the numbers seem too high for a small soft sample? (I triple checked my input dimensions and down speed).
2. I generated another graph from the same data with um on the x axis instead of %. The numbers make more sense this way but I need help equating between this value and the one from the first graph(as they should be the same when manipulating units).
3 To my understanding, area under the curve is toughness which should be provided in units as J/mm3. Does anyone know how to convert the values from the previous 2 questions to J/mm3?
Please help if you understand this problem, it is greatly appreciated!
Regarding the 3rd question, the area under curve represents toughness (amount of work done /unit volume) of material specimen, In you case it is 96.1kPa %. The tensile strength is however, ~580.1 kPa = ~ 0.6 MPa. and the Youngs (elastic) modulus is ~ (580.1 /95.5)*(100/1000) = 0.61MPa
However, i am not sure if there are direct conversion units from Pa% to J/mm^3 .
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Hello, I am wondering if the Rule of Mixture equation is applicable to flexural strength and modulus of carbon fiber composites. If not, what model is the easiest one to predict the flexural properties? Thanks!
In the case of flexural strength and modulus of carbon fiber composites, the Rule of Mixture equation may not be the most accurate method for prediction. This is because carbon fibers have a much higher modulus of elasticity and strength than the polymer matrix, which can result in a non-linear behavior of the composite.
A more accurate model to predict the flexural properties of carbon fiber composites is the Mori-Tanaka model. This model takes into account the size and distribution of the fibers in the matrix, as well as the interface properties between the fibers and matrix.
Another model that can be used is the Hashin-Shtrikman upper and lower bounds. This model is based on the assumption that the composite is made of a mixture of two phases: a stiff phase and a weak phase.
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I am going to calculate Young's Modulus of my hydrogel and wonder what should be the best relaxation time fit for my hydrogel. Also, I would like to know what is the acceptable range for ∆F in equilibrium to plot the equilibrium stress-strain curve.
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Hi,
For non engineering research area, say in plant biology or microbiology, when they do mechanical testing, can we assumed that the reported stress and strain (S-S curve) is engineering stress-strain and not true stress-strain?
I found it quite difficult to do comparison of stress and strain from the literature because of the ambiguity of the reported stress-strain, where in the methodology they didn't specify what type of stress-strain that they used. For example, if one paper mentioned about the maximum stress, is it refers to the ultimate stress in engineering stress, or the fracture stress in true stress?
Hi,
Question still not clear? Could you elaborate more.
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Hi, I am studying the effect of stacking sequences on the energy absorption and specific energy absorption under three points bending load of small beams cut from plates. Indeed, I have manufactured some fiber/resin composite plates from which I have cut some small samples. I need now from the load-displacement curves to get the energy absorption curves and the specific energy absorption curves. All the papers that I found apart from very few are presenting this energy absorption formulas and curves in the case of tubes presenting under crushing load many peaks. Me I have just one peak for each curve. Is there a way to get the energy absorption and the specific one from this load-displacement curves? Thanks.
Himadri Nath Saha whats the difference between this method in the article and simple multiple force to displacement one by one?
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Here I would like to sort of gauge how much extrapolation techniques are still being studied/ used to estimate or predict the remaining life of components that are subjected to creep.
I have come across what is called the Theta projection technique. I have found literature that supports the method impressively well. I was wondering if anybody here used the method or worked with the method closely, so I can ask a couple of questions that I have in my mind when I am applying the method.
I have a question how do you can calculate theta1 theta2 theta3 and theta 4 ?
I want to find constant Theta projection but I don't know how I can find constant.
Thanks
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i want to calculate the phonon spectral  with Negative/Imaginary frequencies signifying instabilities
From your &inputph file, the value for nq1, nq2 and nq3 are for cubic and not for orthorhombic structure.
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The suspension wire of our Shimadzu TGA-50 was disconnected. It was undamaged, so we anchored it back to the balance. However, during our next thermal analysis experiment, we experienced slight erratic increases and decreases in the temperature above 300 degrees Celsius. Any suggestions on how to remedy this issue?
please I need the software for the TGA-50 instrument, Can you help me?
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Hello all,
I am wondering about how the high-pressure mechanical/corrosion test systems in aqueous/gaseous environment (Eg: tensile, creep, fatigue testing in some environments) are made leak proof at the moving part boundaries? Especially when the test vessel is filled with some solutions, how the pull rod - autoclave boundaries are made leak proof? What kind of sealing are used here? Kindly provide me so some design references.
Thank you for your assistance.
I have no experience, with this scenario, but suggest you start by defining the required performance envelope - maximum pressure, temperature range, (if variable), the aqueous/gaseous materials to be used, since those could impact whatever seal material, and the maximum planned individual test duration, in case seal life is limited by chemical interaction with the aqueous/gaseous environment. Then, review the test setup in Fig 1, at the link below, for suitability; it avoids moving part seals by using an expanding bellows type of chamber.
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If R squared values is exactly equal to 0.95, is that significant or insignificant for Taguchi method in case of Mechanical testing of welded joints? Some authors have reported R square values 99.98% and Adjusted R square value 99.97%??
Your opinion is highly appreciated
Regards
Dear Sudhir Kumar,
The R squared is not enough to verify your model. I think you should add a confirmation test and compare the results of obtained value with the model and experiment.
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In a stress-strain curve of an FRP composite, mostly it is represented strain in terms of (%) rather than in (mm). Why it is represented in such a way?
Strain is any kind of deformation, including elongation. Elongation is the word used if we're talking specifically about tensile strain which the sample deforms by stretching and becoming longer. Usually the percent elongation is calculated, which is just the length of the polymer sample after it is stretched (L), divided by the original length of the sample (L0), and then multiplied by 100.
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How much stress can mild steel withstand during compression. I can only find the tensile strength online
Hello All,
Would it be correct to say the compressive strength of S275 steel is almost the same as the tensile yield? I'm looking for data and can't find a great deal
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I want to make a film of sodium caseinate for packaging and mechanical test , but the sodium caseinate doesn't dissolve even in hight temperature and with homogenizer. the film sticks to the petri dish, even in the form of Teflon. I think my method is false . How can I make a smooth and homogenous film that separate of the petri dish? This is my film after drying.
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Hi! I am trying to make tensile dog bones of PVA for mechanical testing using compression molding but I am having some issues.
At first, I am just trying to make films using the hot press before moving on to the dogbone mold. I cannot get the PVA to start melting until about 230C. At that point, the PVA yellows quite a bit, likely due to thermal degradation. Additionally, there are still a lot of bubbles in the film that I cannot seem to get out.
What is the best way to make tensile dogbones of PVA for mechanical testing?
Thanks!
Dear sir you can go for hand lay technique also
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Deseo cambiar mi nombre inicial de Ariel  por César
¿Alguien conoce cómo cambiar el nombre ?
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Hi dears
does any one know how "LCF" Analysis in workbench is done?
note that i know how to do it for HCF.
ANSYS has the "Fatigue Tool", which is a very basic tool I would just recommend for very simple cases. nCode Design Life works well on the WB Platform. Maybe you can try that?
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I have prepared metal joints using microwave energy. Can someone suggest on how to prepare specimen for mechanical testing and SEM/XRD/ TEM analysis? The problem is, after joining, the sample is not getting cut using wire EDM. Secondly, the joint is getting distorted/ damaged upon sample preparation through mechanical working/ machining. Please suggest a solution.
Waterjet cutting is suitable for almost any materials, including very fragile materials such as glass and ceramics.
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Looking for a motivated Ph.D. candidate to work in the field of additive manufacturing with the background of mechanical engineering and material science.
Deadline for application: February 14, 2020
Dear sir,
during my master degree my research work was on laser additive manufacturing.
i would like to pursue my doctor degree on additive manufacturing because of my previous work.
if there is any vacancy on additive manufacturing please let me know.
thank you
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As a 2nd-year PhD researcher, I have been curious about the number of simulation-only PhD theses that exist in fields such as Engineering as well as unrelated fields as well. There is of course value in lab-testing, given how a simulation cannot always account for every boundary condition or factor. Usually, from my limited but growing experience, simulation, in the case of Additive Manufacturing and mechanical testing, is normally used as a validating tool; to help prove in a non-virtual environment what may be seen and tested in the lab, before any kind of scaling or future work is done using simulation (for cost-effectiveness and resource-saving etc.).
But in fields where in-situ testing is normally done, are there PhD theses that "Jump the gun" as it were, and go straight to simulation? Any information on this will be most appreciated given how, in some locations/countries where interaction and access to tools on campus and labs are minimal still due to Covid, improvisations must be made.
Ezekiel Yorke I believe you partly answered your question in the last sentence of the first paragraph-"for cost-effectiveness and resource-saving".
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I am trying to see the effect of modified GO on mechanical properties of CFRP composites. As a part of Mechanical testing, I am doing SENB test. In my understanding, SENB sample should have Notch followed by pre-crack. Can any one help me on creating the pre-crack on SENB sample of CFRP.
Dear Mr. Dilli R Dhakal
I come from reading your question, namely:
“I am trying to see the effect of modified GO on mechanical properties of CFRP composites. As a part of Mechanical testing, I am doing SENB test. In my understanding, SENB sample should have Notch followed by pre-crack. Can any one help me on creating the pre-crack on SENB sample of CFRP”,
published under the title
“How to make a pre-crack on Single-Edge Notched Beam (SENB) sample on Fiber reinforced polymer composite ?” on the ResearchGate platform.
Indeed, notching and pre-cracking are two facets of a problematic topic in Fracture Mechanics testing of polymeric materials. The literature published on the subject is extensive but the information and indications that can be drawn from it are far from being resolutive. The ESIS Technical Committee 4 (a group of experts from both academia and industrial laboratories, voluntarily engaged in the development of protocols and international standards for FM tests on polymeric materials) has been committed to this problem since the beginning of its activity (1985). Much experience has been accumulated and the task of defining a suitable crack starter will hopefully be reached soon: at present a new round-robin (interlaboratory) exercise is currently underway to validate a protocol covering all relevant details of a suitable notching technique for plain polymers. If the outcome of this exercise is positive, the protocol used will be proposed as an ‘addendum’ to ISO 13586:2018 “Plastics — Determination of fracture toughness (GIc and KIc) — Linear elastic fracture mechanics (LEFM) approach”, which is a revised version of the previous ISO 13586:2000, developed by the same ESIS TC4 group, in parallel with ASTM D5045–14.
But you are interested in testing CFRP. More specifically, since you are talking about SENB samples, I assume you mean plastics containing short fibers, not long or continuous fibers, which cannot be tested with SEN samples.
Well: you should know that in the case of short fiber reinforced plastics, the basic LEFM theory can only be applied with some reservations as the material homogeneity hypothesis is not fully verified. The case is dealt with in Annex B of ISO 13586:2018 (while it is not considered at all in ASTM D5045–14), and also in Annex C of ISO 17281:2018, which is an extension of the previous standard to the case of loading rate moderately high (1 m/s).
In particular, the issue of notching is dealt with in clause B.2.3 of Annex B of ISO 13586:2018.
I hope this information will be of help to you.
P.S.- A couple of notes on your question.
First, you write that you want “to see the effect of modified GO on mechanical properties ...” What do you mean by “modified GO”?
Second, in the title that precedes your question, you write “Single-Edge Notched Beam (SENB)”. Please note: B in the acronym SEN(B) stands for “Bend” or “Bending”, not for “Beam”, to distinguish it from SEN(T), where T stands for Tension, which is a possible variant.
@
Sincerely
Andrea Pavan
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Prof. Ing. Andrea PAVAN
former Professor of Polymer Engineering at
POLITECNICO DI MILANO - CMIC Dept. 'Giulio Natta’
Polymer Engineering Laboratory (PolyEngLab)
Piazza Leonardo da Vinci 32, I-20133 Milano, Italy
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By definition, I know Lateral Strain divided by Longitudinal Strain but how to determine this by using Universal Testing Machine or any other method?
what is the procedure to find Poisson's Ratio?
Only with two extensometers mounted on the test piece (one longitudinal, the other transversal) one can measure the Posson's ratio. Only the people equipped to make true stress / true strain tests can do it (and they are not many). I strongly suggest to use cylindrical test pieces and to repeat the test many times, to have a sensible measurement. remember that all materials are anysotropic and this is valid also for Pisson's ratio.
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How to determine the the fatigue values at high stresses ? Because the endurance limit for my material is round about 480 MPa. and the yield point is about 660 MPa.
When I try to find the values in fatigue region at high stresses let's say above 550 MPa and 600 MPa, the material fails immediately after it starts to run and i could feel the heat dissipated. Does it mean anyway that its not possible to have fatigue limit or is it fine to just show the endurance limit ?
In fatigue experiments the material and its microstructure plays a vital role. Its better you tell which material you are using and its composition. Also let me know whether you are using axial fatigue or rotating beam fatigue ,
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I’m searching for possible applications for magnesium wire and rods. I considered fasteners (for example, screws, rivets, and bolts), springs , grids and meshes and bioresorble implants. Also I would like to discuss their potential. I’m not sure if Mg springs could get to industrial use, because of its low Young modulus of 45 GPa. But springs from aluminium with a low Young modulus of 70 GPa is commercially available. In my opinion screws have the best chances because with increasing use of Mg sheets more fasteners of the same material will be needed (e.g. to reduce galvanic corrosion).  Any ideas for other applications would also be appreciated. Thanks in advance.
Dear Johannes Luft,
Since magnesium alloy retains its strength and elongation after annealing at high temperatures , hence its high innovative demand in production technology. Mostly magnesium alloy fine wire is applicable in couple of potentials areas such as;
1. Surgical as Tension band wiring
2. Biodegradable applications, such as suture materials
3. Medical devices (bioabsorbable medical devices)
4. Cardiology; coil stents- potential applications for magnesium alloys in cardiovascular medicine
5. Orthopedic applications
6. Degradable implants with ligatures for blood vessels
7. Motor paddle shifters
8. High purity Magnesium Wire with the highest possible density for use in semiconductor etc.
Hope information is helpful for you.
Ashish
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Which property is very important for stainless steel Spring wire ( 0.64mm)
1.Tensile strength
2.Yield Strength
3.Elongation
This type of spring wire used in Refrigerator door switch.
Some Mechanical Test are given below.
Thank you very much Moe Jmal. It will help full to us
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Hi all,
I'm interested in testing the Hydrogen Embrittlement of several metals. I
Interms of fracture testing and fatigue crack growth rate testing I want to know the difference between the following.
1. Long time H2 exposure in an environmental chamber -> conducting tests in ambient enviroment.
2. Long time H2 exposure in an environmental chamber -> conducting tests in a H2 exposed environment.
In simple terms, the difference between those two conditions is whether or not the environment during testing is allowing the hydrogen to escape from the metal. After removal from a hydrogen environment, most metals will start to lose their hydrogen content, as the hydrogen atoms diffuse out of the material and recombine to escape as hydrogen gas. The rate of this loss depends on the material (particularly characteristics like diffusivity and solubility of hydrogen); a material like a ferritic steel may lose enough hydrogen content within the order of minutes that mechanical tests will no longer show an effect of hydrogen while an austenitic steel may take days to lose enough to no longer show an effect. Testing in a hydrogen environment removes (or at least reduces, depending on pressure) the driving force for the hydrogen to leave the sample.
So, which test conditions you want to use depends on the material being tested and the length of the test. If the hydrogen content loss in on the order of minutes, by the time the sample is removed from the environment, the test is set-up, and then run, it is unlikely that the results will show any effect of hydrogen. If the hydrogen content loss is on the order of days, then shorter tests (tensile, fracture toughness) can probably be run before losing too much hydrogen, but fatigue crack growth rate tests, which can take months, will show a decreasing effect of hydrogen as the test continues.
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Does a single-valued description exist for isotropic materials?
When the crack (be it planar or non-planar) is associated with crack-tip plasticity, the relations between the failure stresses in specimens tested in tension, compression and bending given above (see our answer 1) remain valid, except that σT is now multiplied by a quantity that contains the crack-tip plastic zone size, crack-front shape and orientation of average crack surface. Please see “NON-PLANAR CRACK WITH CRACK-FRONT PLASTIC YIELDING UNDER GENERAL LOADING” in our contributions in ResearchGate.
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Is it possible to do micro tensile specimen of dog bone flat type of ASTM E8 of size 15mmx3mmx1.7 mm on Maraging steels to perform mechanical test?
Yes, you can test. However, it is not a standard specimen size. Hence it is recommended to compare the tensile test result of a non-standard specimen with the standard test specimen. Also, you can report the results with the help of reference where they have employed these type of specimens.
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The material of the specimen is concrete. Three point bending test in my words is synonymous with a Crack mode opening displacement tests with a notch on the bottom surface of the concrete beam.
Has anyone stored the digitize.opk for Origin V.75 and earlier. It is not available anymore on the fileexchange site. Thanks!
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we also want this composite material to be able to be modeled for mechanical testing.
My friend, I suggest you use ABAQUS
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I'm working with a photo polymer resin use blue light to solidifies it. I want to find the Poisson's ratio and shear modulus for solid part after light curing. What testing device or testing method I can use to find these material properties?
The your sample can be measured nondestructively with shear gages and the shear modulus can be calculated from the measurements. A shear gage is a kind of strain gage that is used for testing rigid composite materials. And Poisson's ratio of samples like yours can be measured nondestructively with standard strain gages. As Mohammad Abboud has mentioned, stay in the elastic region of the material (no breaking or plastic deformation - only elastic bending)
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I want to determine the percentage of ductile and brittle fracture for some samples from impact test.
In SEM it is possible to distinguish ductile zone and calculate the percentage.
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I am working on a project on designing and testing new materials and different structure(3D-infill) configurations as prototypes for the mid-sole of a running shoe.
I was wondering about the functional properties that would be required from the mid-sole of a shoe to optimize its performance.
Any leads regarding mechanical/functional properties of running shoes, midsoles or regarding mechanical testing of midsoles would be very helpful.
weight acting capacity, stiffness, material, strength etc.
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Actually i am doing tensile test according to ISO 527 on an injection molded Polypropylene sample with crosshead speed of 10mm/min. The stress strain curve is shown in figure.
Now i want to calculate Youngs modulus, Secant modulus, Yield strength and ET (Modulus at ε3) of this curve. Can someone please help me how to find these for a tensile curve.
Slope gives the Young's modulus.
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I am trying to prepare water-based polyurethane films. When dried air bubbles were formed and destroys the film homogeneity, then I can't use this for mechanical test because of defects. Is there any solution to remove all of the bubbles ?
I recommend you to use a vacuum during preparation
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I need a very precious parameter (length, breadth) for mechanical testing of my composite, so how can I cut my composite sample accurately to carry out the mechanical test (water jet cutting is very costly ).
I used a hex-saw once for the same. We can use milling machines if we have them around... Angle grinders can also be used for cutting the composites. If not we can also use a tiles cutting machine or Plywood cutting machines used in hard ware stores. Depending upon thickness one could also use a Rim cutter (paper cutting machine usually found in offices as a stationary)
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I want to select a mechanical test for fiber/polymer composite to know the effect of fiber percent on composite mechanical properties
I performed the vicker's hardness test but the results were not logical
Pulling the composite specimen under a tensile load is the ultimate litmus test for any improvement in mechanical properties because of the reinforcement. It will plainly expose the real strengthening of the composite material.
Hardness is just a localized indentation. An improvement in hardness can never be counted as strengthening by the reinforcement phase.
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I am studying about Impact load resistance property of Polyurea (Elastomer). With respect to this, I need to conduct tests on this material to evaluate its material model behavior as a hyperelastic material model and Viscoelastic material model. These material models are to be used in an FEA analysis to understand its impact resistance properties. I have researched some data mentioned below about the procedure to determine the viscoelastic properties and hyperelastic properties of an elastomer material.
Kindly review it and provide your valuable comments to improve it against discrepancies incurred by me.
Mechanical tests to be conducted for Hyper-Elastic model
1. Uniaxial Test  (ASTM D 412/ ISO 37)                        -       stress/ strain curve or table as output
2. Biaxial Test (ASTM D 6856 / ISO 16842:2014)        -      stress/ strain curve or table as output
3. Planar Test (                                                                   -      stress/ strain curve or table as output
4. Bulk Modulus Test (ASTM D 575 / ISO 7743)          -      pressure/ volume ration curve or table as output
Mechanical tests to be conducted for Visco-Elastic model
5. Creep test ( Shear, Volumetric and Combined )  (ISO 8013)            -        constant load/stress will be applied as input and  strain/ time curve  will be taken as output
6. Relaxation Test (Shear, Volumetric and Combined) (ISO 3384)     -         constant deflection/strain will be applied as input and stress/time curve will be taken as the output
Test data derived from test no 1 to 4 shall be used to calculate Mooney-Rivlin hyperelastic material model parameters.
Test data derived from 5 & 6 will be used to calculate the following mechanical properties
a. long term normalized shear compliance or modulus
b. long term normalized volumetric compliance or modulus
c. normalized shear compliance or shear relaxation modulus vs. time
d. normalized volumetric compliance or volumetric  relaxation modulus vs. time
The data mentioned from points a to d are needed to derive the Prony series constant for the viscous elastic material model mentioned below:
1. Shear relaxation modulus ratio
2. Bulk relaxation modulus ratio
3. Relaxation time
I have gone through ASTM/ ISO codes mentioned superficially but didn’t understand a few topics for some codes. I need your valuable guidance regarding the following points.
1. specimen preparation (Dimension and Shape)
2. Testing procedure. (Constant Load & Deflection required  in test no 5 & 6)
3. Determination of properties mentioned in points (a to d) from test data output received from test no 5 & 6.
I have followed the procedure described in the file attached for property determination and conducted the test as per described codes.
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Hello everyone,
I am doing machining simulations. For any lubrication assisted machining process, lubrication will decrease the coefficient of friction at the workpiece-tool interface and lubricant will also take the heat out of the system. For the heat taken out from the system, to my best knowledge, I have to measure the heat transfer coefficient. But what about the reduction in coefficient of friction? How can I measure the reduced coefficient?
Dear Rana,
Both pin-on-disc and open tribometer are able to replicate the sliding velocities and contact pressures during cutting to some extent; however, open tribometer can simulate continuous sliding against freshly regenerated surface. The friction coefficient can be measured experimentally in dependence of the relative sliding velocity, contact pressure and temperature during machining with MQL.
The three machining conditions: (i) dry rubbing, representing the dry machining condition, (ii) MQL applied to front face rubbing which was similar to milling with MQL can be applied on the insert rake face and (iii) MQL applied to rear end rubbing which was similar to milling with MQL applied on flank face. Tribological tests can be carried out with coated tungsten carbide pins rubbing on CrMoV5 steel cylinder.
Ashish
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Is there any specific reference such as papers or books which have introduced Concrete aggregates tests under Mechanical and Physical Properties?
For instance, specific gravity is a Physical test property, or Resistance to abrasion is a Mechanical test property, etc.
Thank you for your help in advance.
Dear Mohsen,
You can check this book titled Concrete Technology by Neville and Brooks. Chapter 3 is for aggregate testings and chapters 6, 11, 12, 13, 14, 15, 16 are for concrete testings. The book can be downloaded here:
Good luck
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I'm currently assessing the influence of an additive mixed with epoxy resin that is later used as a matrix for carbon fiber composites. After a tensile test, I was surprised to see that 20 out of the 24 specimens had two ruptures. Some of those showed this 'second rupture' inside the grip.
Is it possible that the results from these tests can still be valid? Or are they automatically classified as invalid/not trustworthy?
Failure in the grips of cfrp laminates is unacceptable. There may be too much stress concentration within the grips. What material are you using as tabs? The thickness of the tab may be too small
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I am working on a route to develop phase pure MAX phases but as with all MAX phase synthesis the formation fo binary carbides hinders this. For some mechanical testing i would like some phase pure samples and thought in the mean time if it was possible to etch away the binary carbide and work with a porous MAX phase that would be fine.
I have found one paper previously that has done this but i cannot locate it anymore with the influx of papers on formation of MXENEs.
Any help would be greatly appreciated
The best procedure to prepare MXenes from MAX phase via:
1- HF
2- HF/H2SO4
3- HF/HCl
No. 1 is recomemnded. recommended
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We have experienced sliver type surface defects in rolling high carbon grade for wire rod. We do not have any clue why this surface defects appears only in high carbon grade and in higher sizes of finished rod. Can anyone explain why sliver type surface defects are appearing in wire rod.Why
I was Chief Technology Officer of Tata Steel till two years ago. Without a proper investigation of sliver defect through micro structural study, any conclusion drawn will not eliminate the problem. Slivers are caused by poor practices in steelmaking, casting, billet dressing, reheating and rolling. A thorough micro structural study along with inclusion analysis by EDS will provide information regarding the sources of the defect.
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I have been trying to solve Stokes equation in 3D micro - geometrical meshed. I'm currently exploring the Fluid model>Creeping flow>stationary of COMSOL 4.4. Comsol failed to solve my problem. It continue showing me "Failed to find a solution. Divergence of the linear iterations. Returned solution is not converged". Going through discussion forum, someone suggested that unchecking "p" on "solver manager" in "solver paramters" would help solve the problem. Please, can anyone help me on how I can locate this solver manager in COMSOL 4.4? Or what is a suitable approach? Thank you all,
Otaru, A.J.
I will address the general solution divergence issue in Comsol. You can try following steps to improve the convergence.
Use structural meshes where you think you are getting the error (or use everywhere), Play with adaptive mesh refinement in solver or adapt option inside mesh node ~ Use this everytime to fine your meshes
Use the Generalized Alpha rather than BDF with strict or intermediate time stepping ~ this improves the convergence in many cases for me
Play with the tolerances (relative and absolute both) ~ sometimes if I change from factor to manual absolute tolerance (with enough time-discretization) it works.
Get the Jacobian update on every iteration than minimum ~ very important for non-linear solvers
Increase the number of maximum iterations ~ good option if you are using very fine tolerances
Change from fully coupled to segregated solvers ~ if you have many integrated physics
Use assembly in geometry and play with source to destination mesh refinements ~ when you are defining BCs or ICs inside the domains
Change scaled values of variables to manual and use values of their respective maximums ~ very helpful at the start of simulation fails.
Regards
Noman
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I think pitting potential andcritical pitting potential are the same and  breakdown potential and transpassive potential also. Is that correct? But the difference between pitting and breakdown potential is not clear.
Hello Manuel, I'm afraid you are missing the definition of pitting potential and breakdown potential. Sometimes they can be the same, as corrosion by pitting or by transpassive dissolution causes the breakdown of the passive film, localized or not. Pitting potential is usually much smaller than the actual breakdown potential due to the smaller potential required to the localized corrosion to initiate.
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I am currently working on a phenomenological creep damage model that takes account of (i) creep cavity nucleation, (ii) diffusion controlled creep cavity growth and (iii) plastic hole growth.
The model gives a good prediction of a wide range of creep-fatigue test data (164 tests) on; Cast 1CrMoV, Cast ½CrMoV, Wrought Grade 91, Cast Type 304L, Type 347 Weld Metal, Wrought Type 321, Wrought Type 316H and Type 316H Multi-Pass HAZ; Tested at Temperatures ranging from 538 to 650°C. (see attached plots).
(Note: The black lines show 1, 2 and 0.5, which are acceptable scatter bands. The red lines show a linear fit to the data and the upper and lower 95% prediction intervals to demonstrate whether the model meets the acceptance criterion. )
However, to achieve a good prediction for all of the 164 Creep-Fatigue tests I have to make some assumptions. I am therefore looking for other evidence (such as metallography or theoretical modelling) that supports these assumptions:
The main assumption that has been made is about the conditions under which Plastic Hole Growth dominates and when Plastic Hole Growth is negligible.
Are there any metallographic observations or theoretical modelling that suggests that; Plastic Hole Growth can only dominate; (i) when the total strain is monotonically increasing and/or (ii) when the total strain exceeds a certain value; or (iii) any other relevant observation regarding Plastic Hole Growth at elevated temperature?
Maybe you can focus on the shape of the cavities.
Assume under uniaxial creep testing:
If the plastic hole growth takes control, then the cavities should be more like a standing needles which is perpendicular to the GB. Otherwise if the vacancy diffusion mechanism controls, the cavities should be like cracks that is parallel to the GB.
But to remember, when the constrained diffusional growth mechanism takes control, then the cavities growth rate actually depends on the slow creep deformation on the neighbourhoods matrix. However, the cavities look like the crack-type, since the vacancy diffusion contributes most of the growth but it is constrained by surrounding slow creep deformation rate. This is the most common type of creep cavitation.
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I want to perform an uni-axial compression test (along with simple tension and planar tension) on a rubber compound to characterize its hyper-elastic behaviour. However, there will be frictional effects causing non-homogeneous strain in the specimen. Can Teflon sheet with some lubricants minimize the friction value close to zero?
Note: I do not have access to Equi-Biaxial tension equipment.
Thanks Gordon and Anton for your valuable inputs.
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I have done spark plasma sintering of the ceramic powder and now i need to measure its elastic modulus , how can i do it without destroying the pellet. I have come to know about pulse echo technique using ultrasonic waves ,but it is vague to me that how will sound waves interact with the porosity in the way
I think both nano-indentation and ultrasonic wave instruments can help you to estimate the elastic modulus of spark plasma sintered ceramics.
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For testing the reliability of a screwdriver, what are the tests used to test these parameters: 1- Brittleness or toughness of the tip screwdriver 2- Tightness of the connection between the shank and the handle screwdriver 3- The limit of bending steel will stand without being plastically deformed screwdriver 4- How much pressure the tip will stand without breaking 5- Twisting effort required to drive the screwdriver 6- The relation between the strength of the tip and the strength of the shank
ISO 2380-1:2004 specifies the shape/form, dimensions and designation of the tips of hand.
It also gives the technical specifications and test conditions for the screw-drivers and, in the case of hand-operated screwdrivers, specifies the test torque which the blade-to-handle connection shall withstand.
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I am working one some bovine samples. I would like to know what mechanical test can give us information about bone behavior and simulates fracture condition
I know that papers in this field have used three point bending and four point bending test
does any one knows more mechanical tests?
can compression test help me in this issue?
As bones are subjected to compression loads. so, compression test is very important for bone.Apart of it, fatigue test is also important because various dynamic loads also act on bone.
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In the material assignment section, I am not able to define the strain life properties of materials (i.e. Strength Coefficient, Strength Exponent, Ductility Coefficient, Ductility Exponent, Cyclic Strength Coefficient, Cyclic Strain Hardening Exponent). Please help me for the same.
HI,
I think, from FEMFAT Material Data! It is a nice way to get input parmeters for ANSYS Strain Life calculation.
Best regards, László
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I performed stress relaxation test, resulting in collecting time, stress, strain. I fitted these data to a 3-decay exponential decay model strain(t)=A0+Ai*exp(-t/ti), with i=1,2,3 and got my parameters A0, Ai and ti. Thus, I calculated modulus of elasticity of the samples.
The fact that in a stress/strain graph the curve given by data of relaxation phase doesn’t coincide with the loading, does not imply with certainty that deformation is plastic, since in the long run it can recover the shape, or am I assuming it wrong?
Is it possible to determine the type of deformation maybe starting from the time constants "ti" - or eventually from other collected data?
If you need to know the 'type of deformation' you have to perform a full cycle in order to assesss if strains can be fully recovered (elastic or viscoelastic behaviour) or not (elasto-plastic or viscous behaviour).
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I have scenario where, It needs to decide whether we can combine two or more variables to form single derived variable. for example: if we have 100 samples of distance traveled and time taken to travel same distance then can we combine these two variables and derive single variable from it like Speed = Distance/Time for all 100 samples. I need some mechanism or tests which should provide me statistical way of confirmation about forming Speed as new single derived variable. Is there any significance test or mechanism to get it done?
Any help would be appreciated and Thanks in Advance!
Many indicators are constructed as functions of several variables not necessarily strongly correlated. The ultimate validity condition is their subject domain meaning. Frequently, they are used to measure a certain distance to an ideal modelling condition. Correlational methods, such as factor or principal components analyses, are very good exploratory techniques but they are restricted to linear relationships between the variables. So, you have a lot of work to do on your own.
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Various journal papers show that many researchers study the effect of process parameters by using bead on weld type and not butt joint weld.e.g. almost all papers on activated tig welding show that welding is done on bead on weld type. What is the reason behind this?
I agree with Prof. Rethmeier. Our X-ray observation results show that the liquid metal may drop down through the gap in the butt welding, which will increase the penetration. Our following papers show the keyhole and molten pool in butt welding situation and bead-on-plate welding situation, respectively.
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Hello,
i want to make some mechanical tests in a cryocontainer with liquid nitrogen as cryogen and no vacuum. The test should be filmed with a commercial camera, which should be outside the container. Thats why the container should have a window. I have seen some publications with those constructions, but in the cryocontainer was vacuum. The question is in first place about the humidity and the danger of steam up. Have someone experience with it? Are there some related publications?
Thank you in advance!
:(
Maybe blow some air through a stack of silica gel?
Or a few puffs from a can of 'dust off' spray?
If aluminium, silicone will stick quite well - so I'd start thinking about cutting a larger circular hole in the case, and gluing a sapphire disc to it. Then, make a hermetic seal with an impermeable blown polymer (even Armacel) and then the second disc glued to that. A sort of annular hamburger - with air space for the beef.
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Since strains measured in the middle of the bars of SHPB by gauges don't represent what happens at specimen/bar interfaces, we must establish calibration files for both incident and transmitted bars. These files will be introduced to a post processing program.
The article, "Evolution of Specimen Strain Rate in Split Hopkinson Bar Test," by H Shin and J-B Kim reports a method of validating the experimental result of the split Hopkinson bar. It cal also be used for the calibration of the instrument. The article can be downloaded at: https://doi.org/10.1177/0954406218813386
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I was trying to print the specimen by 3d printing techniques. Material is prepared by dissolving the Polycaprolactone (PCL) in dicholoromethane. Due to limitation of material syringe size of 3d printing machine, I am not able to print the part according to ASTM D638. Please suggest me any other way to mechanical test the material. Another thing for dimensional inaccuracy is that solvent evaporation. I want to do tensile, compression and flexural testing.
I am preparing the specimen with 3d printing. Our machine is a customized 3d printing machine but having problem of layer shifting. So any other way to make the specimen according to ASTM D638. I was trying to make the specimen with a 3d printing sheet and cutting that sheet into dog bone shape with a cutter. But cutter is creating some notches.
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My samples are hybrid Al nanocomposites. And how can one determine the contribution of each reinforcement in the mechanical strengthening?
As mentioned, for investigating contribution of each reinforcement, micro structural characterization near each interface must be examined. It can reveal about bonding of each contributing reinforcement and can be concluded to the strength provided by separate reinforcement according to bonding achieved and observed through in depth micro-structural analysis.
In the same field we can also do scratch test to see the surface morphology and reinforcing behavior according to the scratch trend near interface areas.
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I took images of surface of composites, but there was contamination such as a square with different brightness.
Because I put specimen with a quite heavy equipment for In-situ mechanical test, It was difficult to eliminate the causes of the contamination completely.
From the images, I was able to get data I wanted, but I wonder If I can use the images with contamination for a journal paper.
It all depends on your discussion. These types of contamination windows are the result of the electron beam polarising, attracting and cracking hydro-carbons on your specimens surface, effectively depositing carbon over the field of view. This gets the more problematic the higher your nominal magnification (smaller scan windows). If it's not a problem for your data interpretation then you can just state it. If your investigation is influenced by it then you need to either eliminate it (clean the surface) or control it reproducibly. A student of mine did a nice work on this topic a few years ago (see AJV Griffths and T Walther, J Phys Conf Ser 2010).
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Pallets are formed of a bio active glass material with the help of polyinyl alcohol on a hydraulic press. The pallet need to dry/heat or not for finding it's compressive strength and hardness.
i think compressive strength is not to need but hardness must be calculated because polyvinyl alcohol may be make any chemical reaction, Hardness of materials is most affected it will be reduce material strength .....
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I'm required to prepare GFRP samples with standard dimensions in order to perform mechanical testing like , tensile, shear, compression ..etc.
How can i prepare these samples ? knowing that i will need to prepare multiple batches for each test ?( large number of samples )
Information:
Matrix: Epoxy
Fiber: Glass Fiber ( Chopped, randomly distributed )
General information like number of specimens, panel size etc are in standards (ie ASTM D7205 / D7205M). If you think about technology one of methods which I recommend is waterjet
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Hello to all the members of the world of science!
It's a tensile-related question and kind of a basic one; but I'd really like to know the answer. So here we go:
Notwithstanding the fact that for most of the iron-based alloys, a rapid fall from upper yield point to lower yield point is witnessed (in addition to the Lüders bands), some iron-based "superalloys" exhibit an almost straight, fall-free form of curve. What is the reason?
Existence of upper and lower yield points is typical for alloyed steels. The reason for that is so called "solute drag", namely: solute atoms' preference to displace in the vicinity of the dislocations (due to an interaction of their stress fields with those of around dislocation core). Thus, when an external stress applied to a sample reaches the vicinity of a yield stress of the material, initially existing dislocations, surrounded (caught) by solute (impurity) atoms, need to additional stress to come off them. This "additional" stress developed onto the loaded sample, is seen as a "higher" yield point. When the majority of dislocations overcome their interaction to solute atoms, the yield point "fall" to its "lower" level. This mechanism works both for interstitial and substitutional solid solutions.
Regarding superalloys, their phase formation should be discussed in details for each specific case separately. For example, for multi-principle alloys (like high-entropy alloys), no "solute" atoms may be defined and then they normally do not demonstrate higher and lower yield points. For intermelallic hardened superalloys, the majority of alloying elements form inermetallide phases, so no "free"solute" atoms exist and then these materials also have no higher and lower yield points.
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I am currently investigating the load-carrying mechanism of a driven pile (hollow bar) and trying to install strain gauge on the pile for measurement of stress distribution.  I have tried to install the strain gauges on both outer and inner surface of the pile with sealant and protective tape on but they all fail due to the large driving force applying on the pile. Most of the gauges broke at the lead wire connections. Is there a way to install the gauges that can withstand large driving force?
Regards, Philip
I am also working with strain gauges pasting it on circumference of the hollow circular pile. I am currently grooving the outside the layer of pile with the thickness of the gauge length of the strain gauges. The wires soldered to the strain gauges were sent from the holes made on the pile above the strain gauges and the strain gauges are then protected with the protective layer given by the HBM. Thus, driving the pile by hammering does not affect the strain gauges and the wires attached to it.
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Where is the stress-strain diagram of brass forging at different temperatures and strain rates?
You can found it in the ASM Atlas of stress-strain curve, pages 523 foward.
If you don't find it, ask me.
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I wish to open a discussion on the way that Plastic Instabilities influence the results of Mechanical Tests. For example, tensile tests, creep tests, torsion tests, pressurised tubes test, etc..
It might be interesting to also discuss tests that are not affected by plastic instabilities; this category might include high cycle fatigue and fracture toughness tests. However, it would be interesting to hear any views to the contrary, such as the need to use side grooves in fracture testing being because of plastic instabilities.
Finally, perhapse I should have re-phrased this question as:
Do plastic instabilities influence the outcome of all mechanical property tests?
Perhaps one should first define what one means by plastic instabilities. As long as we stick to tension, there is no confusion, because the manifestation of instability (necking) is both easily observed and well-defined mathematically.
On the other hand in a test like torsion, it is difficult to establish any geometric instability since the geometry is in principle invariant. Failure simply occurs when a certain condition is reached (consider for instance the max. shear stress criterion); do we consider this point as a plastic instability?
Going further to tests such as compression, where the geometry does change, but in a beneficial manner, making failure less likely. 'Instabilities' in this case would arise from the experimental setup, non-conservation factors like friction, and so on. These are very indirectly related to plasticity.
So at a macroscopic level, the definition is difficult.
At a microscopic level, we may observe certain manifestations; such as flow localisation. People have put forward instability criteria for such cases. These include empirical criteria (eg. Semiatin) as well as criteria developed on energy input/output considerations (eg. rate of energy storage to rate of energy dissipation).But the question again is, at what point do we call it an instability? Stage-I fatigue crack growth is governed by plasticity considerations and Stage-II is governed by fracture mechanics -which of these two is better described as a plastic instability? On one hand it should be Stage-I, because that is 'plastic', on the other hand Stage-II is a more evident 'instability'.
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I have currently tried depositing a sacrificial layer of Polyvinyl acohol and then dissolving in water but it doesn't seem to work great as the it is too strongly adhered to glass, and then if I remove the whole thing, and then place in water, my PVA film deposits but the PCL curls up and can't be used for mechanical testing
At room temperature, PCL is highly soluble in chloroform, dichloromethane, carbon tetrachloride, benzene, toluene, cyclohexanone and 2-nitropropane; slightly soluble in acetone, 2-butanone, ethyl acetate, dimethylformamide and acetonitrile; and insoluble in alcohols, petroleum ether, diethyl ether and water.
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Dear all experts,
I did FEA of nanoindentation with using Abaqus and considered displacement of reference point (RP) on the indenter as a punching tool. Moreover, Abaqus/Explicit method  was applied for solving problems.
But I do not know how to plot Force-Indention depth curve via FEA with using Abaqus.
Any suggestions would be greatly appreciated.
Amin
The reason for you getting the graphs that way is because while specifying the displacement boundary condition you chose an amplitude with a smooth curve. Smooth curve has zero velocity at the start and end as you can see in the displacement time graph. Your force time curve is a result of that
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The modified hall petch equation for subgrain boundary strengthening is:
σy = (B λ^(-1)) + σ0
Where "B" is a constant function of misorientation angle in subgrain boundary and "λ" is the subgrain size.
Dear all
There is a new work that tries to combine both the Hall-Petch and its inverse in one model through presenting a multiscale model that enables description of both the Hall-Petch relation and its inverse in one equation without the need of prior knowledge of the grain size distribution, for more details, please see the following link:
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I have a question about cyclic hardening .
Are the values of Yeild stress at zero plastic strain and equiv stress  identical?
If I have the Cyclic curve for a material (Single hysteresis loop). How to enter this material data in abaqus ??
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Hi all,
I was doing tensile testing on some tiny dog-bone-like tensile testing specimens from an Additively Manufactured Aluminium Alloy 2319 panel.
I got this very weird graph that I do not really understand how can I obtain the ductility, ultimate strength ..etc from.
It shows the Force in (N) VS the machine displacement. (No strain gauges were used).
Can anyone please explain what was going on and how to interpret this graph to extract useful data from?
Many thanks!
Mohammed
Usually using the machine displacement as a measure of strain is not a good idea to obtain a street strain curve. You should be aware that slippage in the grip and deformation in the shoulder section of the dogbone specimen will affect the force displacement curve. If you are only interested in the ultimate tensile strength or the strain at failure, you can obtain the engineering values from the current experiment. But if you want the stress strain curve, you need to use an extensometer or strain gauges.
Regards,
Ali
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Hi,
I have a gel-like polymer-solvent sample which remain as a glassy material at -20 to 0 °C base on thermal analysis experiment. But I would like to confirm whether it is indeed a glass or not. Is there any mechanical test/equipment which can perform at such temperature?
The critical point is that, the sample cannot be exposed to the temperature above this range otherwise the structure will change.
Thank you in advance
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