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Failure Analysis - Science topic

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When applying Maximum Stress Criterion on ANSYS composite PrePost, I noticed that interlaminar stress limit (S3) accounted for by the software is 50% of the out-of-plane stress limit (Z) defined by the laminate properties. However, I didn't find any thing in the documentation that refers to the value of this weakening factor.
Can any one provide me with a reference for this assumption?
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I do not think there is a weakening factor. The values you have are depending on the material properties.
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The Poisson’s ratio is linear and increases slightly at the softening region. Could anyone show light on this? Is there any material model available to simulate this behavior? Thanks!
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No thanks, however just for the sake of curiosity, I invite you to read a litle about 'auxetic materials', if you are familiar with forget my advice. My Regards
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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?
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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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I'm looking for a reference for this equation or another similar one between threshold stress, deformation and pipe thickness for steel pipeline after exposed to erosion and/or corrosion.
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That is a good question.
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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
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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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I hope all the researchers are fine.
Is there is any way to calculate the failure rate per year of lithium ion battery ( as we can calculate failure rate of converters by using MIL-HDBK ).
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I suggest to use FIDES methodology since it has models for Li-ion batteries.
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I am working on developing a micromechanical FE model for predicting kink-band formation in UD composites. To model matrix plasticity, which model, out of Concrete Damaged Plasticity and Drucker-Prager, is preferred? Any insights particularly on the differences between the two models will be really helpful.
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If you want to calibrate a model with a compression test (epoxy shows different response in tension and compression), just use j2 plasticity, available in ABAQUS. All you need is the evolution of the plastic strain and the yield stress.
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I am trying to predict the preload loss in a bot using the analytical relation ( Equation-(28)) given in the paper: . I am not sure How to implement the analytical relation in algorithm. The preload loss seems not to effect any parameter in the Eq-28 except sliding speed to rotational speed ratio. But that dependency of bolt can be neglected based on the assumption of Eq.28 .
It will be of great help if you could suggest something here.
Thanks!
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The torque – tension relationship is highly sensitive to normal variations in the coefficients of friction between threads and between the turning head and the surface of the joint. Refer to the following paper:
Effect of Tightening Speed on the Torque-Tension and Wear Pattern in Bolted Connections
  • Journal of Pressure Vessel Technology 129(3)
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Factors of safety (FoS) are a part of engineering design. For bolts joining, some value of FoS is required to ensure the system safety. Thus, which range value of FoS is suitable for the bolts joining according to its application.
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Nature of load, shear load, ductility etc.
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1. In a Low-velocity impact test, I have got Force vs Time response. There were two peaks in cross-ply and angle-ply orientation. In cross-ply, its peak to peak distance is lesser when compared to angle-ply. What is its significance?
2. Another was, steep rise in the cross-ply but the linear increment in angle -ply. What might be the reason?
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higher stiffness
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Hi
I am looking for datasets that contains the all potential failure of a component. For example in autonomous vehicular domain, If want to see the failure causes of "Camera Sensor", the datasets should contain all possible list of failure cause (Power Outage, Short-circuit, or bad weather condition (reduced perception due to dense fog may be)) of "Camera Sensor"
Thank you
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Jesus verifica el FMEA del producto y de ahí ismo determinas si es Weibull, lognormal, normal, etc. Saludos.
Si es una sola probabilidad de falla o sea alta es Weibull
Si son varias grandes es lognormal.
Si son tres o cuatro muy parecidas es normal.
Eso lo sacar del RPM del FMEA .
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Hey there,
I want to simulate & analyze the fracture and fatigue (crack growth) in the rear axle housing of heavy tracks (Volvo company) in Abaqus.
My question is which method is suitable for this research and how I can find the geometry and the mechanical & fatigue properties for this specific vehicle?
(If there is any related paper/thesis or anyone can help me, please let me know.)
Thank you
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Also, you need to findout the Hashin Damage model parameters for the axle material from the previously published experimental studies.
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For a dynamic Bayesian network (DBN) with a warm spare gate having one primary and one back-up component:
If the primary component P is active at the first time slice, then its failure rate is lambda (P) and the failure rate of back up component S1 is [alpha*lambda (S1)].
If the primary component P fails at the first time slice, then its failure rate is lambda (P) and the failure rate of back up component S1 is [lambda (S1)].
My question is, above are the conditional probabilities of primary and backup component. In a DBN, prior failure probability is also required. What will the prior failure probability of back up component? Will it be calculated using lambda (S1) or alpha*lambda (S1)?
Thank you
regards
Sanchit
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I am looking for a wear detection method for a pipe that goes under intense heat and pressure for short instances at intervals. this process has an average cooldown time of 8 seconds between each cycle.
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Yes, that helps, but, is there a laser inspection method for the same? Hossein Keshtkar
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Dear all,
I am working on analysis of failure in safety valve springs.
I have faced to a special case, wondering if someone could help me.
The pressure relief safety valve hasn't worked (didn't pop) but the spring has failed.
The tank pressure is 90 psi (6.2 bar) and safety valve operating pressure is 150 psi (10.3 bar).
What can be the cause of spring fail?
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What are the most important methods to quantify risk (failures, uncertainties...) for production systems ?
Especially for production systems, We look also on other fields ...
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Thank you for your question!
Failures can occur from engineered, financial, biological systems to most other entities the are at risk. The traditional way to assess failure is through reliability analysis: the distribution of consequences given an event, couples probabilities with magnitude of the consequences. We can extend the idea to developing probabilistic trees (many branches connecting decisions to outcomes) ordered sequentially from the initial decision to the many outcomes. Arcs between them are probabilistic. Bayesian networks are a way to represent a hierarchy of events, their connections, the conditioning (dependencies), and so on. You can also use deterministic networks to understand cause and effect, before worrying about the probability of failure. In my opinion, describing the way events occur, leads to failure or fail for internal reasons is the critical initial step to failure analysis. Here you might think of fault trees and event tress: logical description on how things can go bad, and the ramification of their consequences. So, we have: deterministic representations, probability distributions (consequences or outcomes, frequencies given an event such as a failure), Bayesian networks, and fault-trees, event trees (these are logical maps and can include probability of failure. NASA makes available reports dealing with fault and event trees. There are many other ways; multi-objective decision analysis methods may be important to your work. Finally, keep in mind that many hazardous conditions generate routine and extreme events: their analysis may be conceptually the same but the probabilistic models are less commonly known e.g., fat tailed distributions such as the extended Pareto distribution). So extreme events analysis can be another area of your interest.
Rather than bore you, let me stop here. The book by Yacov Haimes, Risk modeling, assessment and management, 3rd edition, Wiley (2009) is a very good and very extensive reference for many of the available techniques. You might try to get it through an interlibrary loan.
All the best and thanks again.
Paolo
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Hello dear, I would like to do a fatigue experiment on the Ansys program for a particular human bone. I need S-N curve where can I find it away from practical experiences
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You may find these articles useful.
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I wanted to know the common failure criteria used for the analysis of the wooden structure in FE analysis.
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Hi Abhishek Parida, you can find the answers from an ASCE paper: WoodST: A Temperature-Dependent Plastic-Damage Constitutive Model Used for Numerical Simulation of Wood-Based Materials and Connections
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Fracture surface after Uni-axial tensile testing of pure aluminium sub-size tensile specimen shows the presence of elongated dimples instead of equi-axed dimples. What could be the reason behind this? Does it imply that the material failed by shear?
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Akash:
It depends on the size and geometry of your test specimens.
Elongated dimples which form in shear are very common in uniaxial tensile test fracture surfaces. The classical example is the "cup-and-cone" failure mode. In the center of the samples - the "cup" - where the stress-state is dominated by the applied tensile stresses, the process of ductile dimple formation occurs by microvoid coalescence, i.e., voids nucleate at particles (either by the particle cracking or separation at the particle/matrix interfaces); these voids then grow, primarily driven by the triaxial stresses at the center of the sample, until they coalesce or more likely the separating ligaments between the voids "neck down" due to plastic instability. Nominally the same process occurs near the surface of the sample - the "cone" - but now the process is dominated by the near-surface shear stresses. The result is the coalescence of voids formed around particles in shear, which naturally results in elongated dimples.
As you describe your aluminum sample as "sub-size", it is highly likely that the process of microvoid coalescence is dominated by the near-surface shear stresses, in which case elongation dimples would be the result.
ROR
P.S. It is interesting to note here that the formation of dimples both in tension and in shear can even occur at the center of a uniaxial tensile sample in the "cup" region. In many low-alloy steels, the initial voids responsible for their microvoid coalescence ductile fracture are formed at inclusions, e.g., MnS inclusions which readily debond from the matrix. These voids then grow under the triaxial stresses, as described above, but the necking down between these larger voids by a plastic instability can occur by shear-induced microvoid coalescence of cracks in the much smaller carbide particles. The latter is know as a void sheet instability.
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I am using the chi-square funcition to calculate minimal test time (T) in order to demonstrate that the mean time to failure (MTTF) of a product is at least H hours with a confidence level of CL.
I know that I have to use the following formula:
T=MTTF*X(CL,deg)/2
where X(CL,deg) is the chi-square function and deg is the degree number. In all failure analysis text book, deg=2N+2 where N is the number of observed failures. I would like to understand why I have to use this as a degree number.
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I am trying to do failure analysis of randomly distributed CNT reinforced composite.Please suggest me how to incorporate the interface  properties between polymer matrix and carbon nano tube in abaqus /comsol/ansys ?
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If you are still interested on generating randomly distributed cylindrical particles please have a look at this journal paper. I described the algorithm step by step in this paper which enables manipulating the orientation of the particles as well. Basically, with this method you can create a randomly dispersed and oriented cylindrical particles.
Thanks,
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Hello All,
I am new to this forum, I hope this topic is in the corrent section.
I followed a tutorial (attached) to analyse ply failure in composites. I submitted the analysis however it didn't converged.
I'm uploading both tutorial document and my model as inp file. Could you give any suggestion for convergence issue?
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Thank you for your response. I will try to built the model step by step as you advised and share the results.
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Dear all,
Does anyone know how can I estimate the NHPP reliability function through Non-parametric method?!
I know the Kernel density estimation is widely used in this area, but seems it has very complicated theory.
I was wondering if you could suggest an example or statistical software directly.
Also, I am just attaching the needed formulas of Kernel model.
Thanks for your attention.
Best/Hamzeh
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Dear Marcello Fera
I know maybe it is difullcut :) but generally its possible.
Thanks for your answer anyway.
Best.
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What are the values for 1. Maximum pressure at failure 2. Minimum principal strain at failure 3. Maximum effective strain at failure 4. Volumetric strain at failure 5. Number of failed integration points prior to element deletion 6. Number of failure conditions to satisfy before failure occurs 7.Minimum pressure at failure, and other constant present in MAT_ADD_EROSION card.
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hi.
Read papers that are similar to your work and fill those parameters.
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Hello!
I have a metallic rod that is tightened within a metallic tube (with known compression force/pressure applied to the outer surface of the tube). The rod will be moving downwards at a constant displacement (D) by applying axial forces (F) from the top of the rod surface. I am interested in simulating the F-D curve using FEA models and more specifically when the axial slip occurs (failure of the tube gripping capacity.
Could anyone please share any insights on this question? Directions to any relevant papers would be greatly appreciated!
Best,
Yun
Keywords: Slip, Friction, FEA, Coulomb Law, Finite Element, Yield
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It would be good to break the problems into bits:
1. When the rod is pushed, as Prof. Hariharan rightly pointed, the sleeve would act as a mechanism to extrude the rod into thinner diameter. However, where I differ from Prof. Hariharan is that extrusion cannot happen when the sleeve is of constant diameter. The sleeve should be somewhat like a funnel to guide the rod into the die. Also, extrusion involves severe plasticity, which doesn't seem to be your case.
2. I would rather think of the boundary condition as a simple friction clutch (discounting heat effects - assuming quasi static) where the sleeve just throttles the rod.
3. In such a case, when an axial compression is applied and assuming there is no lateral instability (such as linear or non-linear buckling), then the rod should travel past the sleeve - of course, leading to tremendous friction depending on the axial load. Oh! My God!!! There could be local failures such as surface spalling, fretting, heat affected zone, etc.
4. If the sleeve is sufficiently strong and the friction is high, the rod would start to bulge / barrel, if not allowed to buckle.
5.... and so on!!!!
So, you see, you have only told us a small fragment of the problem, leading to multiple assumptions from my side! :-)))
Best would be to draw a free-body diagram that clearly outlines the forces and moments, and perhaps you could use John Harvey's book and use the equations of a cylinder within a cylinder problem... with some tinkering. Sounds easy enough!
To sum it all up, first try approximations and get a hang of the problem before using ABAQUS or ANSYS.
Bests!
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I have written a UMAT code in ABAQUS. This UMAT degrades the young modulus of an isotropic elastic material at a point when the VonMises stress at that point reaches a specific value. It can be seen as a simple progressive failure code. I have applied this UMAT code to a Notched plate under uniform tension.
The problem is that exactly before the damage initiation, the ABAQUS/Standard diverges. I am sure that there is a very simple mistake that I just can't see!
:)
I have attached the Input file of the model and the UMAT code. I will be so thankful if anyone could help.
Thanks in advance
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I think the original code is correct @ Domenico De Rosa, since the secant modulus is used to model progressive damage. In which case, DDSDDE is the secant modulus (which is decreased to model the progressive material degradation), therefore, the full-scale constitutive equation instead of the incremental constitutive equation should be used.
In this problem, the damage takes place in one increment, where the damage parameter D changes from 0 to 0.99999 abruptly, which will cause numerical instability. I would propose several approaches that might solve the difficulty:
1. If applicable, the most straightforward way is to decrease the damage parameter from 0.99999 to a smaller value (e.g., 0.9 or 0.95), which will greatly facilitate convergence.
2. Instead of modeling the damage in one step, try to use a "real" progressive damage process. A simple model would be linear degradation. See following for example codes. Note that D increases from 0 to DMAX, when Mises stress increases from STRESS_INI to STRESS_FAL.
IF (SMISES .GT. STRESS_FAL) THEN
D_temp = DMAX
ELSE IF ( (SMISES .GT. STRESS_INI) .AND. (SMISES .LT. STRESS_FAL)) THEN
D_temp = DMAX * (SMISES -STRESS_INI) / (STRESS_FAL-STRESS_INI)
ELSE
D_temp = 0
END IF
IF (D_temp .GT. D) D=D_temp
3.Element type also have great influence, based on my personal experience, 2nd order elements help in some cases.
When modeling damage, convergence is so annoying that it often makes graduate students Crazy. Hope these suggestion will be helpful~
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I am working on cohesive contact(Between two Aluminium bars). I just have some questions that I am wondering if anyone can help me by answering them.
1. How can I find the the parameters in traction-separation: Knn, Kss, Ktt ( should I consider module of shear and elasticity for them?)
- In damage initiation: normal, shear 1, shear 2 (would I consider tensile and shear strength for these values?)
- In damage evolution: fracture energy. mix-mode ratio 1 and 2
2. From where i can get this parameters ??
I'm looking forward to hearing from you soon.
Thank you,
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knn, kss, ktt should be taken as large as possible to avoid collaps of contact point. the usual convention is E/t where E is the modulus and t is the thickness of adjacent layer. similarly G12 and G23 for kss and ktt. for damage initiation both shear can be assumed to be inter-laminar shear strength i.e S12 and normal as strength of matrix. these assumptions are quite appropriate. this is extended for damage energies too.
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I trying to make failure analysis of prestressed concrete. I tried using Ansys but it doesn't converge. How about Abaqus?
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Yossi Reichman ... I recommended ABAQUS
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Looking for a device to analyse a large sample during 5min.
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Maybe Aidlab (229$)? Here's the article how can you connect Aidlab's ECG readings with Kubios: https://medium.com/@Aidlab/exporting-your-ecg-readings-with-aidlab-4dd5c049078a
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Dear researchers.
I've modeled an Eglass/Epoxy composite plate containing a hole in the center and is tensile-loaded from both sides. Hashin progressive failure in Abaqus software is used to see damage in all failure modes. As i excepted , for example Matrix Tension Failure, matrix damaged regions should be shown in HSNMTCRT parameter in Abaqus results but as you see in attachted figure (1), in spite of different amounts of HSNMTCRT parameter, all model have the same gray color .
Why ? Do certain settings are required in the software ?
Thanks
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it is for over values of the range!
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This an internal surface of a crude oil pipeline, API 5L X52, the pipe was dented on this area, so flow turbulence may occur produce erosion as shown in the Figure.
My question is, what type of erosion this could be, erosion-corrosion, cavitation erosion, or just erosion?
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Can you please give more details about inner scale XRF, oil analysis, pressure, water salinity since the eroded surface reveal different kind of corrosion rather than erosion.
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Dear colleagues
I am trying to acquire the graph of probability of failure versus factor of safety. In other words, I would like to depict a figure in which the vertical axis shows the probability of failure and the horizontal axis shows factor of safety.  As a result of random set theory, the cumulative density function for factor of safety has been calculated. That is to say, there has been a graph in which the vertical axes shows cumulative density function and the horizontal axis shows factor of safety. The question arises here, how the probability of failure for each factor of safety would be derived from cumulative density graph of factor of safety?
Should I use fragility function in order to obtain probability of failure?
I would be pleased to give you any further information that you may request.
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By definition, a slope fails with a FoS going below 1.0. As long as the FoS is above 1.0, a slope is considered stable. Thus, I do not see how your figure could be drawn.
Of course, the FoS is a simplification and can not be measured directly. However, the definition is rather clear and if you follow it a FoS>1 relates to zero probability of failure.
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I am currently working on NFMEA composite analysis in ANSYS workbench, i have tried ACP also but due to the lack of software knowledge i didn't get the desired failure criterion to do failure analysis could anybody help me with it?
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This is similar to yield criteria for isotropic material. However you have to supply 21 elastic constants to software. useful commands are FC, FCLIST, and FCDELE. 
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Topics related to failed knuckles
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Dear Phemelo Modise,
I am not getting your question. What you want to know? What you you want to investigate, is it for developing new composition, new heat treatment procedure or to improve mechanical property? Which aspect you want to know or want to explore in Grade-E casting?
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It would be nice to have a root cause failure analysis guidebook to validate some of the common failures I am witnessing in pipes and other materials on an industrial plant near me.
I remember an old mini guidebook that one of my professors had in his possession titled "Root Cause Analysis Guidebook" by Chun Choi that he used quite frequently in his reports. However, I was not able to find that book online anywhere for some reason. I am not sure if I have the title correct.
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Please refer atteched reference book by Donald Wulpi on failure analysis of industrial components.
SHIVRAJ SINGH KASANA
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As we may know, non-local plasticity formulations are utilized to reduce mesh subjectivity and eliminate numerical instabilities like snap-back in the response behavior of the materials under plastic regime.
Just wondering which parameter(s) you prefer to "non-localize" to achieve better result? particularly, why averaging the internal variables (hardening/ softening/ cohesive strength modifier) is not recommended compared to plastic strain?
And the most important question: What is your recommendation in implementing strategy of such formulations? I'm trying to implement it in FORTRAN as a UMAT.
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Is there any reference stating that "it is not recommended to average internal variables?" Actually plastic strain is also based on an internal variable (plastic multiplier or whatever you call it). If the plastic strain tensor is averaged over some elements, then the difference obviously is that in one case a tensor is averaged as opposed to a scalar.
I dont know what specific user subroutine is necessary to gather information from neighboring elements, but surely there must be one, if it is not UMAT.
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I am working on a simulation involving perforation of sheet using LS Dyna 980 but I am unable to get element deletion in simulation.
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As mentined before, to know your problem it is necessary to define the options that you are using in oyur model.
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Dear all,
I really appreciate it if someone could reply my question.
The parameters based on NHPP are Shape= 0.46, Scale= 20.54.
and operation time
0, 50, 100, 200, 300, 400,..., 1000
for more detail, please find the attached file.
I do not understand why the reliability values are unreasonable!!
Thanks in advance,
Hamzeh
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Dear Prof. Naderpour.
Thank you very much. I appreciate your reply.
Best wishes,
Hamzeh
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Geophysical survey
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Foundation failure analysis depends on the shear strength parameters of the soil, foundation shape and depth and water table level.
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I want to compare the effect of a special heat treatment on LCF behavior of a Ti alloy which is usually being used in aero engin compressor parts.
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Dear Manoranjan Jena
It was a very nice and informative conversation.
I wish you the best things.
Best Regards
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I am using beam elements to analyze a frame. To simulate deletion of the failed beam elements, I have added *MAT_ADD_EROSION (Element formulation type 1:Hughes Liu with cross section integration) and used maximum principle strain as failure criteria, but simulation does not show element deletion/failure.Does anyone have any ideas about the use of erosion keyword for beam elements?
Thank you
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@ Aleem:
Although, element erosion should not be used to delete elements because if the erosion deletion criterion is set too high, element distortion will occur, and if it is set too low, premature deletion will occur. If it is necessary for you to use element erosion, especially for large deformation in the post-failure region, you could make the failure principal strain a higher magnitude of the peak strain. This also depends on the material model you are using in your simulation.
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pin on disc wear sample of aluminium fly ash composite material.
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There are more than 35 wear mechanisms available for failure of metal under sliding wear. This wear on this picture appears to be adhesive wear.
The terminologies brittle and ductile failure is commonly applied to materials failure under tensile load.  
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when post curing applied to thermoset resin, a significant decrease in room temperature storage modulus is observed during my experiments. As far as i know, as the x-link increases , modulus also increases. What should be the explanation? Is this also an indication of decrease in tensile strength, can we correlate these directly?
Loss modulus is decreased and broadened as it is expected. But what happens to Storage modulus?
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Hi Deniz,
Can you share your graphs?
 It seems a contradictory result.
I am really keen on to dig its root cause.
Sincerely,
Amin
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energies involved in ductile failure
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Plastic and surface
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When joints open while the adhesive is still rather liquid, structures like shown in the pictures can be detected. These structure are very helpful in failure analysis as the prove the rather low viscosity of the adhesive in the moment of the failure. We called them honey on toast structure for the lack of a better term as they resemble the structure of a honey covered toast after falling on the wrong side. But is there somewhere a real/better term for this structure? Are there publications about the dependency of the structures on adhesive thickness and viscosity?  
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Meanwhile we found some literature and scientific names for the structures. The structures resembling natural valeys/rivers (my first 3 pictures) can be addressed as: fingering, viscoelastic fingering or air fingers. To my understanding, they are no fractals, as the self-similarity stops at an early scale. The honeycomb-like structures (last picture - red) are adressed as cavitation in the literature.
According to literature and some own experiments, fingers and caviations depend on the following aspects: In the case of air (or an other low viscosity material) beeing present, factors that facilitate the flow of the adhesive lead to fingers. Conversely, factors that inhibit the flow of the adhesive lead to small fingers and promote the appearance of honeycomb structures (cavitation). Fingers can only occour if air is present. Fingers are promoted by a low internal friction (viscosity), a slow speed of separation of the parts and a high thickness of the adhesive layer. If no air can penetrate into the adhesive, only cavitation are formed. Cavitations originate from unavoidable preexisting bubble nuclei in the range of a few µm that enlarge when pulling forces are applied
Amar MB, Bonn D, 2005. Fingering instabilities in adhesive failure. Physica D: Nonlinear Phenomena 209, 1–16. DOI: 10.1016/j.physd.2005.07.002.
Nase J, Derks D, Lindner A, 2011. Dynamic evolution of fingering patterns in a lifted Hele–Shaw cell. Physics of Fluids 23, 123101. DOI: 10.1063/1.3659140.
Poivet S, Nallet F, Gay C, Fabre P, 2003. Cavitation-induced force transition in confined viscous liquids under traction. EPL (Europhysics Letters) 62, 244.
Poivet S, Nallet F, Gay C, Teisseire J, Fabre P, 2004. Force response of a viscous liquid in a probe-tack geometry: fingering versus cavitation. The European physical journal. E, Soft matter 15, 97–116. DOI: 10.1140/epje/i2004-10040-2.
Saffman PG, Taylor G, 1958. The Penetration of a Fluid into a Porous Medium or Hele-Shaw Cell Containing a More Viscous Liquid. Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 245, 312–329. DOI: 10.1098/rspa.1958.0085.
Tanguy F, Nicoli M, Lindner A, Creton C, 2014. Quantitative analysis of the debonding structure of soft adhesives. The European physical journal. E, Soft matter 37, 3. DOI: 10.1140/epje/i2014-14003-8.
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My research is in the field of failure mechanisms of metal components in cyclonic wind events.  I am seeking to establish the effect of resonance of steel strucures induced by wind to estimate survivability of a structure.
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Hi all;
I want to use AFT models to predict the time of tumor recurrence in an specific cancer type. To be more precise, I want to use regression in order to predict the survival time. Consider the following equation:
T=x*B+e
where "T" is the survival time, matrix "x" has the features for different samples, "B" must be a sparse weight vector and "e" is the error.
I have used this regression model and the results are poor for the prediction. However if I use the logarithm of "T" the error will fall down and the results will be perfect. But my question is:
For the sake of computing the error of my prediction, should I convert the predicted values (predicted T) by taking exponential of them or not? Or generally, after using AFT should we take exponential to remove the effect of the logarithm in the regression?
any suggestion would be great help to me
Thanks in advance  
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i think, it needed to take an exponential of predicted T if transformed logarithomic values of T were used into the model
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I've found "Standard Practice for Investigation and Analysis of Physical Component Failures (Withdrawn 2004)" ASTM E2332-04 and "Standard Guide for Corrosion-Related Failure Analysis" ASTM G161 - 00(2013)  only. 
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I know the adhesive properties, but how to design CZM in lap joint using ANSYS ?
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First  you have to model that zone then you have to add the material properties in a different material model. Then during meshing you have to chose the mesh tool > global set (click)> new window come there you have to put that material no. which have CZ properties?> then mesh it.
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Hi everyone!
I would be very grateful for any advice on the following topics:
1) What are the tasks where predictive analytics is most efficient if we are talking about freight operating companies? What predictive analytics methods can be efficiently employed?
2) What are the best publications to start with?
3) Is there any info available about real projects that have been successfully implemented, what ROI can we expect?
Many thanks!
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Hello,
I recommend:
Solutions predictive diagnostics of vehicles and infrastructure.
Implementation by railway industry Big Data technology is predictive analytics.
Best Regards
Arkadiusz Kampczyk
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I had a reviewer claim that using accelerated failure time models to see how various personal characteristics vary with graduation rates is implausible because they are designed for events that always must happen (e.g., death, failed light bulbs, etc.). 
In practice, I've seen both survival models and AFT models used for child welfare placement, foreclosures and other disease outcomes. ' As far as the explicit assumptions I have found from Swindell (2009):
“The AFT approach requires that experimental data satisfy certain assumptions. In particular, the treatment effect on survivorship should be roughly consistent throughout the lifespan, and survival times are assumed to follow a parametric distribution that must be specified (e.g., exponential, Weibull, log-normal, log-logistic).” (p. 3)
It is probably the case that the effect on survivorship is not consistent through the lifespan in the case of graduation, and parametric assumptions are usually false, but at least these assumptions are more or less testable. I also reviewed Allison (2009) and Kalbfleish & Prentice (2002) and cannot find such an asssumption. 
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AFT models usually focus on the time of failure, not explicite to the event. Problematically the fact is more complicated, if you analyzing recurrent events.
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I am preparing fused silica ceramics with gelcasting technique. The sample (30 mm diameter X 120 mm length). The samples are failing at the sintering process. Please tell the reasons for the failure? Suggest any methods to find the failure analysis?
The sintering temperature is 1250 oC with an heating rate of 2 oC holding 2 hours and cooled to room temperature with furnace on in the nitrogen environment.
I am attaching the figure of failed sample.
Thanking you in advance. 
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There can be many causes of the problem, but the most likely is the partial crystallization of the amorphous SiO2 to cristobalite. This crystallization means a large volume change, which may cause cracks.
An X-ray diffraction analysis can prove the formation of cristobalite.
Against cristobalite formation may help lower sintering temperature, the faster heating rate and shorter holding.
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I have been trying to implement such a model in a UEL in Abaqus for a long time, but I always get unphysical results when the cohesive crack is activated.
I made very simple hypotheses to get it run:
  • linear elastic material
  • One 2D FE loaded in uni-axial tension
  • When the y-component of the stress exceeds the cohesive strength, the cohesive crack is inserted with a pre-defined angle (for simplicity I don't calculate the angle from the stress state at crack activation)
  • I am using a linear softening cohesive law (extrinsic, so without an elastic part) in shear and normal directions (so that t_n = t0_n - T_n * [[u]]_n and the same for shear). The initial traction t0_n and t0_t is calculated from the tangential and normal stress projection on the cohesive crack, i.e. t0_n = n*sigma*n and t0_t = t*sigma*n)
  • My problem is that I don't get a reasonable solution when the crack is inserted. I guess that it might be due to the non-satisfaction of the traction continuity in the X-FEM leading to the compensation of the traction difference by an unphysical crack opening. But I am not that sure.
It would be great to find other researchers who have already implemented such a model. It would also be interesting to know whether there are others who had a similar problem at crack activation. And if not, I would be very pleased to have more fruitful discussions on that topic.
I will also upload my UEL and the inp file, in the case that someone is interested to take a look inside.
Thank you very much in advance!!!
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I have some experiences with cohesive cracks and XFEM. Did you resolve the step that lead to crack initiation? And if you use small steps the problem you mentioned becomes negligible.
Please let me know.
Best regards,
Phu
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Hi, Thank you for any advices.
     Assume if I want to estimate the sum value impact of evrey variable in order to select the best variable. It is not sensible to calculate impact of each value in the variable domain beacause of the high computation cost, Are there any methods to reduce that computation cost? 
Thank you for any advices.
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Hi, I want to know how to put a much greater emphasis on failures during propagation to guide the search in Constraint programming. Are there any good techiques or strategies about this? For example, when propagate the search, I apply the impact of a assignment as  reduction of  the search space, but when the assignment result in a failure, how can I put a much greater emphasis on the failure. Thank you so much for all of the replies.
best regard
Meko
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One easy approach is to penalize the objective function. Specifically, in a optimization project of minimization, results that against the predefined constraints will be assigned to a great value (penalty). In this case, the proposed solution that fail to satisfy the constraint(s) will never be the future candidates in the following generation. 
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There is a Johnson cook model for ductile material deformation. One is material model and one is failure model. when the fracture occurs in ductile material due to shear . Triaxiality is low for that .
Does this model suitable for low triaxiality range. 
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Dear A. Morasch,
Thank you ,my confusion is clear now.
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IR laser tool is generally used for inspection/failure analysis.
I would like to know the impact of IR energy on transistors/CMOS circuitry
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agree with the answer given above.nice description.
Regards
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To mimic loading and unloading phenomenon using Abaqus I have  tried applying load (as displacement, say from 0 to 1mm) in 1st step then in 2nd step I have changed it gradually to its initial value (zero). But, I am not getting expected result in terms of load vs deflection plot. I am getting some amount of residual reaction force at the end of analysis, but I want to free the model from it. Also, when the load is decreasing from its peak value (1mm), for the first increment (decrease in terms of displacement) the reaction force is increasing surprisingly. Please suggest me any procedure to get exact result. Thanks.
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Thanks Baeker Sir and Ramsay Sir.
Thank you Mr. Hamad for your excellent suggestion. Its working perfectly and I am very happy.
I have tested my model for a lower load like 0.5mm (in terms of displacement) where there is no failure and the model works perfectly. The loading and unloading both  curves are linear and in same way as shown in attached figure.
For higher load also now it's working well using the method suggested by Mr. Hamad. The new Reaction force vs. Displacement curve is attached for displacement upto 1mm. There is no jump in reaction force during 1st unloading time and also residual reaction force amount has also decreased from 11.4N to 3.5N which is very less compared to the maximum reaction force.
Thank you once again all of you.
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Hi
I am working on stochastic progressive failure analysis of laminated composite plates. Kindly suggest me how to choose degradation model in post first-ply failure.
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Hi. it is depend on your strategy. you can use the sudden degradation models  based on the stress analysis and some relevant criteria such as Hashin-Rotem or use the gradual degradation model (Crack density based model) using the energy criterion. 
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I am trying to find the probability of failure of each individual volume element of a body,  by using Principal of Independent Action (PIA) failure criteria.  The problem is that the formula uses the state of stress(SoS) of element but , I have the SoS of all its 8 nodes ( obtained through FEA in  ANSYS). How can I use the failure criteria ( PIA )formula now or is there any way to find the SoS of element from the SoS of nodes.
Your advice would be much appreciated . If further details are needed i can submit a report to you .
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Hi,
First of all, stress from FEA will not be calculated at the nodes, they are calculated at integration points (also known as material points). For full integration, there are 8 integration points and you will have stresses at all these integration points for single element. If you choose reduced integration there will be only 1 integration point and you will get single value of stress for an element.
Though I do not know about this failure criterion, my suggestions will be independent of the failure criterion used. You can do following things.
Apply failure criterion for each integration point and check the status. If all material points of an element shows failure, that means the element has also failed.
or
You can check, stress values at all integration points. If they are not very different from each other, then probably you can take value of stress at the Centroid of the element (that will be simply the average of stress from all 8 points). Considering stress at Centroid to be representative stress of that element, you can check the failure criterion, if satisfied you may consider element as a failed element.
Hope this helps.
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Am doing failure analysis for liners used in ball mills.
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May I know? the Mn-Steels based either ferritic or austenitic composition range.
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I am planning to conduct FMEA study for some of the existing equipment/device.This device has several models, most of them have almost same design features. I wish to find out the weak parts/sub component of these device type by conducting the study.
Since number of different models of this device are available in the market, it is not possible to conduct study on all the models.
Whether it would be appropriate to conduct FMEA study on specific model and conclude the results for the whole species of the devices?
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As long as the different models are similar in functions, it is more efficient to maintain a single FMEA to cover them. Within the single FMEA, it is possible to denote some failure modes as specific only to Model X.  Or you could add an extra column to input which are the applicable equipment for each line item.
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Reliability of PV modules
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Thank you very much Dr Zekry
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I want to do FE model of the failure in material and the literature has used ansys for the analysis , and i want to do the analysis in abaqus and would like to know if there are any equivalent for the same
warm regards
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Dear friend, very interesting question. I am interested to your question and will explain in detail soon (similar to my case). A bit hurry for this time, please remind me.
However, the easiest way is searching the related document by typing the keywords into google scholar. You will find some related articles.
If yet to find the articles, do not hesitate to let me know. InsyaALLAH I will help you in detail.
Good luck. Dr Zol Bahri - Universiti Malaysia Perlis
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Hi all,
I would like to know if someone know the data from a white paper/report/research paper about
-> SoftErrors: Failure in Time (FIT) rate (neutron/meoun/proton etc.) for some Flip-Flops which are based on FinFET and/or FDSOI technologies. As there are few papers available on SRAM FinFET FIT rate. Furthermore, there are few papers on CMOS FIT rate for flip flops are also available.
Thanks.
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Hi,
I don't have direct access to any white papers on flop SEU and FIT rates but I can say that in typical designs, the FIT rate of sequential logic, at least in terms of retention cross-section (without accounting for logic or timing derating - if you want to include this, and assuming a flop has the same fail rate as SRAM, derating will reduced the actual flop error rate to 5-10% of the measured retention value in most logic designs), is about the same as that of the SRAM - in other words if you put and array of flops in a neutron beam/alpha source and an SRAM array with the same number of elements as the flop array, the failure rate will be similar. It is true that flops with higher drive transistors (wider gates) can have a reduction in failure rate but we usually see all flops from a technology library from the weakest to the strongest are about 2x higher than SRAM (in the same technology) to about 15x lower failure rate, In a FIINFET technology I would expect the same trend to be followed since the sensitive element in the SRAM and the flop is the same or similar FinFET transistor.
Sorry if this is to general for you needs, but if you are trying to design experiments, the rule of thumb above has worked for many generations of bulk and SOI devices and I assume will work for FinFET as well.  
One note, I am assuming you are referring to standard flops and not DICE or some other redundant flops which, of course, would have a much, much lower failure rate.  
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Recipe is to etch oxide, nitride, or maybe TiN layer and some passivation layer.
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Usually, using F-ion to remove Si-ion, and C-ion, H-ion to reactionwith O-ion to reduce the concentration of F-ion, other bombardment was reaction also for expose ionic bond or removed some hard removed chemical such as Ti. Any quesiton, you could reach me by mail. tao.wang@diasemi.com
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I have to perform the ball on flat reciprocatory wear tests oh IF steel and Mild steel, for the very same purpose I have to select the ball material which should obviously be more harder that the steel itself.
Confusion is between Al2O3 , SiC, Ni and WC balls.
And could you guys please provide me with references ?
Thanks
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Dear Murkute: an additional aspect is the level of adhesion observed after sliding. Pay attention on it and this point can be useful for your definition. Regards.
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Where can I find some reliability data for steam traps? I am looking for Mean life, MTBF and Gamma life for say 250 psi, 1/2" inverted bucket type steam traps. This information is required for the reliability analysis of the steam system. Please share any any information, failure data or any specific experience you may have in this field.
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No ready-made data is available, at least to me. But you can proceed in the following steps:
1) Collect failed parts data from warranty and/or testing
2) Use the data to estimate reliability
If you do not have and/or can't arrange for any data, then look for MIL-STD (freely downloadable). You may find gross estimate of failure rate.  
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I want to apply cyclic load on the blade to inspect it under fatigue loading. 
I want to save the blade and I do not want to causes failure to it. 
I'm looking for a methodology that can help me in estimating the number of cycles to failure by certain applied cycles. 
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I think fatigue life test in general is a destructive test. If you are interested in obtaining experimental values , I think you should proceed till obtaining the required no. of cycles then stop, If the blade persists I think this means that the test is successful.
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I am planning to model a brick masonry wall to check its failure mechanism on non-linear time history and provide RC jackets to retrofit this wall in both in-plane and out-of-plane directions.
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Hi Sandip,
Similar work has been done in Abaqus focusing on steel reinforcements.
You can get ideas from this report:
Regards,
George
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I am working on using non-linear ultrasonic parameters, specifically, the ratio of the amplitude of the secondary harmonic to the fundamental to quantify creep damage in austenitic stainless steel.
I have a couple of questions about the results, like the peaks I see in the waveform, etc.
It would be of great help and interest if somebody knows about this particular application of ultrasonic testing.
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Jitendra, 
I have read your papers. It is a huge part of my PhD thesis, the concept of NLU and your work is the main inspiration. One of the first papers I read. 
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When we finish the compression test and obtain the true flow stress curve, as shown in the attached figure. In addition, if we know there is crack along the shear  band, as shown in the second figure, can we recognize the failure initiation strain from the true stress-strain curve in the compression test directly? How can we obtain the failure initiation strain from the test flow stress curve at the given condition? Thanks in advance. 
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The question demands numerous implicit assumptions from the responder.  Determination of mechanical properties normally depends on the assumption of uniform loading, and Considere's method can be used in a tensile test, to determine the onset of necking.  Then Bridgman's analysis can be used to determine the true stress during deformation after necking develops.  In the compression test there are complicating factors, such as the greasing of the platens.  How does the questioner compute "true stress" if the stress state and the specimen shape are continually changing?  So is the questioner presenting the unidirectional engineering stress based on the initial specimen cross sectional area?  Is it a cylindrical specimen?  As other responders have suggested, the answer depends on the purpose of the experiment and the criteria for the mechanical properties, as well as the ductility of the metal.  Eisenacher's answer is reasonable with a quibble about the failure being complete over the section.  If the metal is coming apart in shear, it may not be complete across the section.  So what is the criterion for failure?
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we will find the liner relationship between reliability and risk in the maintenance, Determination index that show weight tow criteria: risk and reliability
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Thank you very much, it was great
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I am studying the debonding between the broken carbon nanotube (CNT) and the matrix in CNT-based composites. A 3D square representative volume element (RVE) with one CNT fiber surrounded by matrix has been considered. Considering a very small debonding around the fiber break as a crack front, the strain energy release rates (SERRs) are to be calculated using virtual crack closure integral (VCCI) method to assess the propensity of such a crack to grow leading to complete fiber debonding.
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