Science topics: PhysicsMechanics
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Mechanics - Science topic

Mechanics is the branch of science concerned with the behavior of physical bodies when subjected to forces or displacements, and the subsequent effects of the bodies on their environment.
Questions related to Mechanics
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I am looking for information on the pressure tree roots (by expansion) can exert on structures as retaining walls and quay walls. Failure of retaining walls by root pressure is very common. Is there any way/model to determine this load?
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There are some experimental papers on force measurement by plant tree roots:
You may use an inverted analysis of paper B with rod theory to derive root pressure.
Hope it helps
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What characterization required for automotive anti-roll bar applications?
Mechanical, Dynamic mechanical, thermal etc and what is range of vales of these properties
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Dear Karthika P,
Don’t copy paste articles from Google on a subject which you don’t know anything. To understand Automotive Dynamic Systems is beyond your capability.
regards
jasbir s ryait
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I am simulating a welding process. Do I have to use merge nodes as well as the spot welding together?
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No you do not need to do this. If you merge the nodes the contact will lose its function.
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The results seemed to go against the laws of physics: The vacuum, by definition, is completely empty space and does not exert friction on objects within it.
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Hello,
One of my colleagues is working with piezoelectric components and couldn't find the shock response spectrum for various piezoelectric components. Can anyone please share your idea to deal with the calculation process of shock response spectrum (srs) of piezoelectric components? However, any informative links that contain useful resources or details will be very helpful.
Thank you for your time and guidance.
Best wishes,
Faishal Rahaman
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I have a RG write-up for the impulse excitation of a piezoelectric shock sensor (PSS), which you may find of interest for your current problem, see, . I just uploaded this Method today, 3/2/2022. I hope this helps.
Regards,
Thomas Cuff
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What is the relationship between the polar moment of inertia and the torsional constant?
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I guess is * τ = T r / Jp0, where:
τ - is the shear stress.
T - is torque.
r - is the distance from the axis of the torsion.
Jp0 - is the polar moment of inertia.
so Jp0 ~ τ-1 T r
cc Wiki russian article, Best Regards.
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I have just designed a fuzzy system, and now I want to redesign it based on the fractional order. However, I have no idea where to start from and what to do. Could you please tell me what I should do and mention any related sources to study?
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Dear s.Milad:
You can benefit from this valuable article about your topic:
"Fuzzy Fractional-Order PID Controller for Fractional Model of Pneumatic Pressure System".
Abstract:
This article presents a fuzzy fractional-order PID (FFOPID) controller scheme for a pneumatic pressure regulating system. The industrial pneumatic pressure systems are having strong dynamic and nonlinearity characteristics; further, these systems come across frequent load variations and external disturbances. Hence, for the smooth and trouble-free operation of the industrial pressure system, an effective control mechanism could be adopted. The objective of this work is to design an intelligent fuzzy-based fractional-order PID control scheme to ensure a robust performance with respect to load variation and external disturbances. A novel model of a pilot pressure regulating system is developed to validate the effectiveness of the proposed control scheme. Simulation studies are carried out in a delayed nonlinear pressure regulating system under different operating conditions using fractional-order PID (FOPID) controller with fuzzy online gain tuning mechanism. The results demonstrate the usefulness of the proposed strategy and confirm the performance improvement for the pneumatic pressure system. To highlight the advantages of the proposed scheme a comparative study with conventional PID and FOPID control schemes is made.
I hope it will be helpful...
Best wishes....
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Please, see the attached file RPVM.pdf. Any comment will be wellcome.
More on this subject at:
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I think that an interesting point is that, using units with c = 1, the 4-velocity (dt,dx,0,0) is a 1-tensor that is the same for any offset of clocks of the inertial frame. Then we have that the 4-velocity (dt,dx,0,0) transforms the same for any synchronization, it satisfies the Einstein addition of velocities and consequently it also satisfies the principle of constancy of speed of light. On the other hand, as it behaves like a tensor under Lorentz transformations, the relativity principle holds for it an for all derived 1-tensors like velocity, acceleration and so on.
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You can find the wording in the attached file PR1-v3.pdf. Any comment will be wellcome.
More on this topic at:
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I think that an interesting point is that, using units with c = 1, the 4-velocity (dt,dx,0,0) is a 1-tensor that is the same for any offset of clocks of the inertial frame. Then we have that the 4-velocity (dt,dx,0,0) transforms the same for any synchronization, it satisfies the Einstein addition of velocities and consequently it also satisfies the principle of constancy of speed of light. On the other hand, as it behaves like a tensor under Lorentz transformations, the relativity principle holds for it an for all derived 1-tensors like velocity, acceleration and so on.
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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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Assuming we have a piece of timber C16 - 100x100x1000mm and we apply UDL + a point load at middle point on it (parallel to the fibre) as shown below, how much will the timber compress between the force and the concrete surface ?
I have attached a sketch as well. Please see below.
If you could show a detailed calculation would be much appreciated. Thank you!
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Kindly find my working if you need more tutorials you can follow me on research gate. I can teach you for free.
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Hello all,
I´m currently working for a medical device company. We are trying to understand the buckling effect during an insertion force test.
We use a flexible PVC extrusion with these properties:
Hardness: 95 (ASTM D-2240)
Specific gravity: 1.73 (ASTM D-792)
Tensile strength psi: 3400 (ASTM D-638)
Elongation%: 250 (ASTM D-638)
100% Modulus psi: 2860 (ASTM D-638)
This extrusion is inserted into another medical device and the force required to insert the extrusion must be below 4 lbf. However, it is noted that during insertion procedure the extrusion buckles, losing force and failing test. The extrusion is inserted using a fixture to guarantee that 4lbf are being applied, there are some cases where the readings of the force tester are below 4lbf but the extrusion get stuck and didn't pass all the way thru the medical device not reaching the desired end position. Our guess is that the column force is lost as result of buckling.
Extrusion length is about 10 inches, OD is about .077” and ID is .035”, this isn’t a solid extrusion. For this case, we would like to know much force (lbf) can be applied to the extrusion before buckling. Seems like we might use Euler formula, but it is unclear to me how to use the formula adding the factor that this isn’t a solid column, I assume wall thickness may be considered.
I appreciate any help to solve this doubt.
Thanks!
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A quick check with pens and papers-
Use Euler's Buckling formula
max load P= EI*(pi)^2/L^2. L is the insertion point (into hole, box, whatever) to holding point (where the pipe is gripped and applied force. E is young's modulus. I is area moment of inertia, I=(pi/64)* (D^4-d^4). D is outer and d is inner dia of tube
This bold portion would work just fine to use the area moment of inertia of a hollow column.
For eccentric loading, use the Secant formula instead
But wait! if PVC tube is way too flexible to be considered to be elastomeric rather than linear elastic, there can be error, because Euler's formula was derived for linear elastic deformation of columns.
If standard simulations (Solidworks, Comsol, Ansys) seem too hard for you, go to some user friendly online simulation interfaces like simscale. Just upload 3D image of files in their simulation IDE, give input parameters, and you are done within a few minutes to hours.
Go for it.
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how to create a custom output time (t) -Displacement (Uy) in a transient analysis ???
I want a macro gives the following output;
t-time y-disp
1 0.00000E+00
2 0.00000E+00
3 -0.18027E-01
4 -0.36054E-01
5 -0.54260E-01
.
.
.
I used this code in a static analysis it worked
*get,far,node,,count
*dim,matrice,array,far,3
/post1
set,last
*cfopen,temp,txt ! Create file called “temp.txt”
*vwrite
('x-dist',8x,'y-disp',10x,'z-disp')
*vget,matrice(1,1),node,1,loc,x
*vget,matrice(1,2),node,1,u,y
*vget,matrice(1,3),node,1,u,z
*vwrite,matrice(1,1),matrice(1,2),matrice(1,3)
finish
The above macro creates the following output:
x-dist y-disp z-disp
0.93 0.00000E+00 0.00000E+00
0.96 0.00000E+00 0.00000E+00
1.00 -0.45562E+00 0.00000E+00
1.00 -0.47383E+00 0.00000E+00
1.00 -0.49186E+00 0.00000E+00
0.96 -0.50988E+00 0.00000E+00
0.93 -0.50988E+00 0.00000E+00
0.89 -0.50988E+00 0.00000E+00
0.86 -0.50988E+00 0.00000E+00
0.82 -0.50988E+00 0.00000E+00
0.78 -0.50988E+00 0.00000E+00
0.75 -0.50988E+00 0.00000E+00
0.71 -0.50988E+00 0.00000E+00
0.68 -0.50988E+00 0.00000E+00
.
.
.
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This is a good question.
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Is there any defined radii ratio with respect to the plate thickness exceeding to which an annular plate may be treated as a ring? Moreover what changes in vibrational behaviour may be observed when we increase the radii ratio of an annular plate and make it a ring?
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Nitish Kumar Guru I have added the example to the PERMAS4EDU project. See the project log at https://www.researchgate.net/project/PERMAS4EDU
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Hi. I have a gel aspirated in a rectangular tapered microchannel at deltaP pressure. The channel has the same height everywhere. But the width changes uniformly. The purpose of the experiment is to find Young's modulus from Hook's law. For that I will need stress along x, y and z axis. Along x axis, the stress is deltaP. Along y axis the stress arises from the wall stress which is a function of deltaP and angle alpha as shown in the figure. I am not sure how to calculate wall stress along z axis. Should it be equal to stress along y axis? Also, should I sum two wall stresses in the y axis as there are two walls to calculate overall stress?
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Dear Sirs,
The elevator example in general relativity is used to show that gravitational force and an inertial force are not distinguishable. In other words the 2nd Newton's law is the same in the two frames: inertial frame with homogenous gravitational field and the elevator's frame without gravitational field which has constant acceleration in respect to the inertial frame.
But every one knows that an inertial force is a force which does not obey the 3rd Newton's law. For example such forces are cetrifugal force and Coriolis force existing in the Earth reference frame. Gravitational force satisfies the 3rd Newton's law. So one can conclude that the gravitational force is not inertial.
Could you clarify the above controversy.
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Dear Sirs,
R Feynman in his lectures, vol 1, chapter 12, Characteristics of force wrote:
"The real content of Newton’s laws is this: that the force is supposed to have some independent properties, in addition to the law F=ma; but the specific independent properties that the force has were not completely described by Newton or by anybody else, and therefore the physical law F=ma is an incomplete law. ".
Other researchers may consider the 2nd Newton's law as a definition of force or mass. But R. Feynman did not agree with them in the above chapter.
What is your view on the 2nd Newton's law?
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Dear Mr khripov,
I prefer that we agree on the questions you ask.
For me F'=-kx is Hook's law.
For me F=ma is Newton's second law.
If in a given problem F=F', then -kx=ma.It is Newton's law particularized to the case where the force applied is that of a spring (Hook's law).
At static equilibrium, we have theoretically kx=mg. The theory tells you that kx=mg.
You want to check this relation experimentally. Fabricate identical objects of the same mass m. Hang on the spring one object, then two objects, then three objects, etc.... At the first elongation mark the elongation with a pen x=X0. You will notice experimentally that for 2m you will have an elongation of 2(X0), for 3m you will have 3(X0), etc ..... Plot on a graph the elongation of the spring as a function of the hooked mass. You will see that the curve is a straight line and that the slope of this line is (1/k) in the system of units you have used.
Conclusion:
1) You have therefore verified the linearity of x as a function of m and this is the verification you wanted to make.
2) You have deduced the value of k.
Important remark:
Clearly, the measurements you have made do not depend on any law (including the law of the relation you want to verify).
I hope I have answered your question.
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Hello,
I'm trying to model a transient heating process in COMSOL with a thin metal film on a polymer substrate. I'm trying to gain intuition into the mechanical and thermal properties as a function of temperature. In particular, how do the heat capacity and Young's modulus of polyimide change with temperature especially near or above the glass transition temperature.
Regards,
Adam
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Hi,
I wonder how torque changes with different angles of the torsion axis. Please find the attached figure. I can see how to find out T1 (Blue colour) but not T2. Do I have to compare cross-sectional areas? It would be great if someone can share your thought on this or any formula on this.
Regards
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Sorry Jelong Lee, now a understand your question. There will be two component for the torque: one in the direction of 1 and other in the direction 2. In the direction 2 is a different deformation, I am not sure if the formula above applies, I think L should be much bigger than the other 2 dimensions of the beam.
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Dear Sirs,
Everyone knows the derivation of Lorentz transformations from electromagnetic wave front propagation. But Lorentz transformations are the basis of the general mechanics theory. It seems to me it is logically correct to derive the transformations from purely mechanical grounds. But how to do this? Mechanical (sound) waves are not of course applicable here. Or there is only purely mathematical approach? I The later is also not good in physics. Could it be derived from gravitational wave propagation? If it is so is there any controversy because General relativity is based on special relativity? I would be grateful for your suggestions.
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Length contraction CAN be deduced by purely mechanical processes. The other Transformations are substituted by other mechanical means. For example, time dilation can be speed of light changes in different media density.
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Dear Sirs,
I would like to find out whether galilean relativity principle (which means the same
form of three Newton's laws in all inertial frames) is derived from the three Newton's laws or
any other classical mechanics statements.
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Galilean relativity principle is the statement that Newton's laws are invariant under the transformations of the Galilean group. And this can be checked. Conversely, the equations of motion that are invariant under the Galilean group, describe Newton's laws.
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Are tire damping co-efficient and stiffness material-dependent properties or related to tire pressure?
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Both the parameters are considered. However, many more parameters are taken into account while varying the stiffness and damping coefficient.
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Hi everyone, recently i have a question about how to calculate the orthotropic elastic matrix of cancellous bone cube. I really need the help!!!!
I applied six stress states to the cancellous bone cube by ABAQUS and got an anisotropic stiffness matrix whose every element has value (because the material coordinate axis is not consistent with the local axis) as shown in figure.
I changed the anisotropic matix (6×6) to a fourth order tensor Cmnpq.
I really want to rotate Cmnpq to an orthotropic fourth tensor Cijkl by the following relation:
Cijkl = RimRjnRkpRlqCmnpq,
the Rim is an rotation (3×3) matrix as shown in figure. The α, β and γ is the angle of rotation ( euler angle) about z-, x- and y-axes.
Now my idea is that, we can calculate brute-force the all rotation angle α, β and γ by 1 degree increments. When sum of C14, C15, C16, C24, C25, C26, C34, C35, C36, C55, C56, C66 of matrix is minimum closely to ZERO, the Cijkl is orthotropic tensor. And my question is:
  • what scope of α, β and γ should I give in Python procedure? I can get all rotation situation.
  • If I can use any optimization algorithm? rather than brute-force calculating by 1degree increments. Such as POWELL algorithm and how to use?
Thank you very much!
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check the uploaded doc maybe it will help
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Dear Sirs,
I did not find this material on the internet. There are only mechanical models of some aspects of self-replication. Full mechanical model is absent. Of course it is enourmous problem if one precisely build it. But maybe there are simple and simultaneously more complete mechanical models? I prefer purely mechanical self-replicating machine but self-replicating robots are also good.
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The first mechanistic model of self-replication was given by John von Neumann by his self-replicating cellular automaton. He was followed by others: Langdon, Reggia, ...
It would be interesting to study this research stream as it provides great insights into creation of mechanistic description of certain properties of living structures.
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Hello!
Could you tell me - I need to simulate what forces are generated in the rotor of an electric machine when it rotates. Also, inserts of other materials are made in the rotor and this must be taken into account. As I understand it, you can take this into account by setting a Contact Pair, but the model takes a very long time and does not produce a result.
Please tell me if I'm doing everything right and what else is needed for a full analysis?
Thanks in advance!
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Modeling Rotating Electrical Machines in COMSOL Multiphysics
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Hello,
I would like to know what are the commutator systems that are being used in other labs for in-vivo neural recording (and stimulation) in rodents?
In the lab we tested some cheap non-motorized commutators such as adafruit's and moflon's. The initial mechanical resistance is very high for a mouse to easily make it turn.
I know there are some motorized options but they are super expensive (>4k) and/or super big (need to be installed in the ceiling)
Thank you!
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Hi Sirenia,
My message is probably too late. How is your experience with those swivels?
We use a similar swivel for recording rats. They work well mostly but one of three or four makes some noise during spinning. But in generally we are satisfied. Now fortunately there is a big selection of different swivels in amazon. I guess that a bit more expensive one conducts a a better quality signal.
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I need the basics for including energy loss in Hamilton formulation for Finite element analysis for vibration of viscoelastic materials. The papers I read use complex modulus to represent viscoelastic losses or convolution integrals. Can someone give me a link where the formulation starts from Hamilton's principle?
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Have you got answer about it?
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I would like to know, which books are internationally recognized for studying Mechanics, Molecular Physics, Waves, Electricity and Magnetism, Optics and Atomic Physics. Russian favorite authors are Irodov and Saveliev. But I want to know what books are traditional for English speaking auditory?
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1)Berkeley Physics Course
2)Alonso-Finn Fundamental University Physics
3)A.N.Matveev 4 volumes; Mechanics, Electricity and Magnetism, Molecular Physics and Optics
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I have a block of mass 'm' modelled as a spring-mass-damper system. A horizontal force F is acting on the mass as shown.
  • spring constant = k;
  • damping coefficient = c.
Most of the models I see has a vertical push/pull force on the mass. Then the free body diagrams becomes easy. How do I make a free body diagram in this case? Also, I am mainly interested in Moment induced on the bottom hinge point.
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The first option is a special case of the second one.
In other words, if the stiffness of the springs is too high, both formulas will give you the same answer.
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Dear Sirs,
The 1st law in Newton`s principia are now understood as two statements: the determination of inertial frame reference (if F=0 then a=0 and if F is not equal 0 then there is some body accelleration "a"); there is in nature at least one inertial frame reference. Theoretically I can understand it a little bit. As we have such a determination of inertial frame reference then the 2 nd Newton law is not directly followed from the 1 st law, or this determination is partly independent of the 2nd law. So it looks like logically good.
But what we have in experiment? I do not know whether there is any research on experimental determination of any particular inertial system (like International Celestial Reference System) using the 1 st Newton law. So in practice we use the 2 nd law (e.g. school example - foucault pendulum plane rotation). Could you clarify on the experimental and theoretical determination of inertial frame reference. You know there are teachers that see the 1st law as the consequence of the 2nd law.
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The Galilean invariance, Dr. Anatoly A Khripov, the laws of motion are the same in all inertial frames if there is no acceleration due to an external force. But sometimes a conservation law (momentum, or energy) is needed experimentally to be tested.
For example, the capillary movement without viscosity of the 4He isotope is based on the Galilean invariance of energy and momentum, despite it is a quantum liquid, showing how general is the Galilean invariance.
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I am confused with co-efficient of friction and friction factor.
A part of a Fluid Mechanics text book says that in Darcy-Weisbach equation
hf=(f L V2)/(2g D)
f is friction factor.
In the same time, it says that in below equation the f is co-efficient of fraction.
hf=(4f L V2)/(2g D).
In this case, we see that (Friction factor = 4 x co-efficient of friction).
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Does anyone know the exact name of the following equation used for friction factor calculation?
f=16/Rek
1/√f= G log (Rek√f)-H
that G, H, k are constants that have different values.
what dose the index of k shows?
i want to know how i should choose the correct value for each constant
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I am looking for information on advanced characterisation of mechanically activated fly ash. Advanced characterisation I mean, quantitative XRD for estimation of amorphous phase, IR, NMR and XPS for bonding, etc, Can anyone help about publication(s) on the subject?
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We activate alkali activated hybrid cement in standard cement ball mill already couple of years as mentioned in older answer
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Hi,
I am trying to model a free-free body (aircraft) as a stick-model only consisting of beam elements. For certain configurations I observed that my Stiffness Matrix loses singularities / my model has an insufficient number of rigid body modes. I broke the problem down to a simple 2-D Beam configuration shown in the attached picture. The model consists of 5 Nodes with 3 degrees of freedom per Node all connected via Euler-Bernoulli-Beams with the analytical Stiffness Matrix shown in the picture. The left configuration exhibits the expected behaviour having 3 rigid body modes. Introducing the additional stiffening beam element for some reason reduces the number of rigid body modes, as indicated by the higher Mode 3 Frequency and the higher Rank of the Stiffness Matrix. Is such behaviour expected? And if yes, what are ways to workaround this problem other than building the model from 3D solid elements?
Thanks for your help!
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Conclusion: Were indeed purely numerical issues. To my surprise beam length errors and node position errors of a magnitude of 10E-6 [m] resulted in a rank deficient Stiffness Matrix.
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Find the reaction at Point A and B.
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Dear Kanticha,
You can easily get the answer by parsing the reaction vector A.
you can see in following PDF.
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I want to convert the Young's modulus and Poisson ratio of an orthotropic material given in Cartesian coordinates into cylindrical coordinates. Please suggest me the way or provide me the link or document where I can get these things. Thanks in advance
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Also note that under the same loading the deformation of material with rectilinear orthotropy differs from the deformation of materials with cylindrical orthotropy.
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Hi everyone,
As far as I know, the user-defined forces can only be applied to elements (VDLOAD). I could not find in the manual any subroutine to apply user-defined forces to the individual nodes instead of elements. I thought about adapting the VDISP to provide "forces" in the form of incremental displacements/accelerations, but I was hoping that there is some other way to achieve this. On a related note, how about Abaqus Standard?
Thanks!
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hi Andrew
i have some ideas about your question but i am not sure about them.
for apply nodal force in Abaqus you can use input file. in input file you can apply concentrated force to any point you want.
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Dear Sirs,
I think many knows the ideas due to Jules Henri Poincaré that the physics laws can be formally rewriten as a space-time curvature or as new geometry solely without forces. It is because the physics laws and geometry laws only together are verified in the experiment. So we can arbitrary choose the one of them.
Do you know any works, researchers who realized this idea. I understand that it is just fantasy as it is not proved in the experiment for all forces excepting gravitation.
Do you know works where three Newtons laws are rewritten as just space-time curvature or 5D space curvature or the like without FORCES. Kaluzi-Klein theory is only about electricity.
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📷Preston Guynn. added a reply on June 19, 2019:
Force, mass, and energy are a parallel set of descriptions of the effects of special relativistic Thomas Precession. All matter and space, and their interactions are described with distance in three dimensions, time, and their derivatives.
Newton's first law of motion is , "Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it."
Yet the concept of motion requires at least two objects, and if there are two objects, then there is always an external force, which is gravitation.
So the idea of rewriting Newton's laws without force (or mass or energy) is good, but it should be extended to incorporate the most basic non-linear effects of motion in space time, which are special relativity and Thomas Precession.
See my article describing the recent discovery of the effects of Thomas Precession the particle and galactic scales.
Article Thomas Precession is the Basis for the Structure of Matter and Space
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Is ECU connected to can? Can we program it through AUTOSAR?
And if we have up to 70's ECU in car so it means we don't have a brain here?
What is sbw-Center ECU then?
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Dear Fatemeh Pourhashem,
The ECU( Engine Control Unit (ECU) uses the camshaft and crankshaft position sensors to determine where the pistons and valves in the engine are at any given time. The ECU uses all of this information to start and keep the engine running.
ROM displaying method of automatically identifying sensor locations in an ECU’s can be effective. This can be able to create a data representation of the functions within a binary and their internal control flow graphs. Adding ECU can be effective for engine family. Addition can be able to successfully locate 95% of all candidate functions and was able to successfully recover 100% of likely sensor addresses within each of those functions.
Ashish
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Why many scientists use the term mathematical model ?
If you have a certain phenomenon and you want to model it, you will describe its, more or less, approximate behaviour by applying to it laws which can be physical, chemical, economical, geometrical and so on, depending on the phenomenon.
Mathematics is only a tool to describe these laws, so you should speak of physical, chemical, economical, geometrical  ... models and not of mathematical ones.
Most of the models I encounter in my research are physical models because, to build them up, the laws of physics are used.
Each time I hear the term mathematical model, my nose gets wrinkled.
What is your opinion ?
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I agree with Abdulrahman Dahash
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One of my friends is studying a bachelor's degree in mechanical engineering and going to finish it at the end of this year. he wants to continue his studies; therefore, I am searching for him exciting areas.
Could you please give me a piece of advice to find proper topics or draw an outline of trending fields in mechanical engineering?
PS: he does not have an academic email to sign up in RG.
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  • Biomedical and Engineering Fluid Mechanics.
  • Combustion and the Environment.
  • Ground Vehicle Systems.
  • Heat Transfer, Thermodynamics and Energy Systems.
  • Manufacturing.
  • Mechanical Design.
  • System Dynamics and Control.
  • Transportation Systems
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Hello,
According to the power law, Stress=K*strain^n. Could someone please explain why an increase in strain hardening exponent n results in less material necking from this equation?
Please see the attached plot, here I used K=1 to ignore it's effect and I have varied n for n different values.
It seems that for the same stress put into the material, the curve at n=0.1 produces the smallest strain, where as the curve at n=0.5 produces the largest strain, up to strain=1. If the stiffest material is desired, is n=0.1 not more favourable here?
This behaviour changes at strains greater than 1, this has also left me confused.
Any clarification on this will be very much appreciated.
Thank you!
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according to the change of the behaviour at strain=1 this is purely mathematical since the exponent is n<1 (it's like the behaviour of square root). I believe that you care about cases with strain values much lower than 1. So, an increase in strain hardening exponent n results in less material necking since it represents a more "elastic" material behaviour. Check the following:
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DIssipation is the reflection of irreversibility in the processes of nature. How does it reflect itself in various laws an principles ?
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It's very simple - the more scattering channels and bandwidth of these channels - the more dissipation. And vice versa.
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I have a Scenario where my lock nut is tightend using a prevailing torque of 14 Nm (as mentioned by the manufacturer) on to the rotor placed between bearings (But the tightening direction and the rotor rotating direction is same unfortunately). The lock nut is loosened after particular life cycle of usage as the rotor rotates with a acceleration of 1230 rad/sec and every time it starts, the sudden acceleration loosens the lock nut. Is there a simple approch to calculate a appropriate prevailing torque for this situation, so that the lock nut does not loosen up when the rotor starts accelerating towards it's max RPM of 9400 in 1 second?
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Unfortunately, what you have here is a classic case of "jerk". It will not matter how well you calculate the theoretical torque required for the nut to hold fast, in practice it will always come loose. It is the same principle as the tool used to remove wheel nuts. You have to change the physics of your assembly. If you can, reverse the thread direction of the nut. If you cannot, you have to find a way of clamping the nut. Solutions depend on the size of the nut. How big is it? Knowing this, I can give you a way of locking the nut that does not depend on the torque that you are using.
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The material should be stiff, tough or Young modulus should be more or which property should be significant for excellent energy absorption?
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Thank you Ashish and Alpesh. The toughness and resilience are calculated when tensile load is applied. Will a material absorb same energy when a impact load is applied such as bullet fired on the material front face?
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Hello, world
I've run a 3D simulation of solid mechanic when I'm trying to use contact pairs.In the model I have three parts, the first is constrained, the second is the membrane which is in contact with the first part and the thirth is where I prescribe a displacement and I'm looking the deformation of the membrane.
My issue is that the solids don't interact with each other, one go through the other one like a ghost.
Does anyone here have any experience with contact modeling in COMSOL? Anyone know how to fix this issue?
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Contact problems have improved in Comsol since recent releases. You can define the penalty stiffness/ coefficient (very high) to overcome the solids penetration issues.
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I basically want to know know any connection if machine learning in Mechanics.
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Optimization looks a promising start for machine learning in mechanics. Even in expensive simulations like crack propagation u can build few models to get the results and then train ur models based on input data. Which can be further used for collecting more results or for optimization purposes.
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I am designing a helmet impact machine. Does the accelerometer placed inside helmet and load cell placed under anvil give the same peak force value?
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Hassan, its a bit more complicated than that. Because, the accelerometer measures acceleration (in meters per second squared), whilst the load cell measures the force in N (kg.m.s^-2).
Of course the force (which the load cell will measure) of the impact will cause an acceleration on both bodies. But whilst the force is equal and opposite, the acceleration won’t be. Even more issues arise if the helpmeet deforms irreversibly to absorb the impact - which I guess is the idea of it. I would both sensors....
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I would like to know a finite element software which provides open source codes for large deformation analysis for beam and shell elements.
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Thank you Sriram Ganesan
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For a hard surface, it is commanly assumed that the maximum value of friction only depends on the coefficient of friction and the normal reaction force. However, intution suggest that is should also depend on the contact surface area, as it does in the case of skin friction drag force (friction between a solid and fluid) which indeed depends on the surface area under concideration. So the question is what is the fundamental microscopic reasoning for this assumption that it the friction is independent of contact area?
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Maybe it is more intuitive to think about it on a stress-level.
Think about a body with weight F [N] that is placed on a surface with friction. Let the contact area be A [m^2].
The normal stress in the contact area then follows to:
sigma [N/m^2] = F / A (1)
This leads to a resistance against movement due to friction (mu [-]) of:
tau [N/m^2] = mu * sigma (2)
So every part of the contact area contributes to the resistance against movement. However, for the resisting force V [N] you have to sum up the stresses.
V = tau * A = mu * F (3)
So I think you could say that the contact area matters in a way. But what really matters is the product of the contact area and the normal stresses and that product stays the same for different geometries as long as your body has the same weight.
Hope that helps :)
Regards,
Stefan
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I am wondering and doing a research project to find out if having personnel who are cross-qualified like A&P Mechanics with pilot training or pilots who have mechanic training make a difference. Do Aircraft maintenance release teams who have no, or limited, pilot training negatively affect aircraft return-to-service rates or is there no affect on how the return-to-service rate. Where could I possibly find information regarding the return-to-service rates for the aviation community?
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I am not aware of any sources for historical return-to-service rates; you would probably have to do a study by recruiting Mechanics and looking at their current rates, or asking if shops have data of when the planes went in vs when they went back to service. Granted, the type of service will affect the results. If a mechanic is highly certified and regarded and is only given the complex problems to solve, of course their solutions will take longer, so maybe you can consider a way to classify the work done on the aircraft.
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As shown in illustration, I have a pipe with details listed below and it is clamped at both ends. Clamps are tightened by applying a torque of 15Nm. How could i find out if the support provided between the clamps, in this case a U bolt supporting at a length from one end of Clamp would be sufficient under 1G loading condition.
Total length of pipe = 4 meters
OD=5"
Wall thickness = 1.5mm
Total mass of pipe = 5 kg
Thank you all folks out here..
Appreciate your help.
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Hi, Apart from axial guiding function, there is perpendicular load to resist as well, which is a combination of temperature and pressure.
The U bolt has to be sufficient strength and stiffness.
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i have generated some graph using ansys mechanical apdl.....now, i have to find FFT transformation of the figure which is in time domain............i can do it once i get x and y data value of figure............if anyone knows to extract x and y data from graph or perfom FFT of function from graph, then pl. help me
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is it possible to extract mode shapes from ansys mechanical apdl to a spreadsheet on excel.
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I wanna to calculate the fatigue life of rotational structures, first I need to know their mechanical loads
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Dear Maryam turbine blades are in contact with the working fluid. Drag and lift forces act on the blades. To determine the forces you must know about the type of the turbine (radial, axial). And the power and speed.
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specialy in mechanical engineering
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additive manufacturing have the vast scope including some specified rapid prototype strategy...SLS, SLM, SGC, SDM, LRP,Mold SDM, DLF, BPM, 3DP etc.
Smart manufacturing
Nano-manufacturing
Molecular level manufacturing
Atomic level fracture continuum mechanics
Mechatronics still it has very good research challenges and opportunities.
Control and precision engineering
Generation of electricity sustainable energy approach
Hope it work out for you.
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Why and How the stress triaxiality in a material becomes greater than 1? What is the physical significance of it?
Kindly throw a light on it.
Regards
Aditya
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Sorry to disagree. There are two ways how stress triaxiality can build up at the material point: under quasi-static loading it is the result of the stress gradient associated to geometry changes and stress concentration. The upper bound value for this is 3. The second way is because of stress waves interactions in dynamic impact. Under planar impact (uniaxial strain condition) stress triaxiality increases linearly with the uniaxial strain. Depending on the ratio of the bulk modulus and the flow stress. To give you an idea in pure copper it reaches 22 and more. Under ideally hydrostatic condition it becomes infinite ;)
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Please suggest some papers for Elastic constants of polymethylmethacrylate (PMMA)?
TIA
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The necessary information contains the attached paper:
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I have a fluid mechanics questions. Suppose that we a submillimeter needle that is already inserted in the soft tissue. water can run through this needle if the pump is on. suppose we turn the pump on. Waterjet with initial velocity of v0 starts to cut a channel in soft tissue. There is also backflow as this cuts the tissue (backflow from the same cut channel). my question is what happen to the velocity of the waterjet when it hits tissue and goes through backflow. Is it time dependent? Is it depth dependent? Experiments showed that it is velocity dependent since the depth of cut reached from 0 to say 4 mm in 30 second and after that it increases with the order of like 0.01 mm. So it got me thinking that velocity is depth and time dependent. My pump provided volumetric flow rate Q ml/min so the average velocity of waterjet at the nozzle is v = Q/A.
I have developed a mechanics based model for waterjet based on tissue properties and waterjet needle properties including velocity of waterjet. However for Q = 50 ml/min and 0.32 mm needle the velocity is approx. 10 m/s. including this velocity in model predicts a depth of cut in the order of meter which it should be in the order of mm. How can I include the effect of depth and time in my velocity. Any help is greatly appreciated.
Please also see the attached cartoon for a simple demonstration.
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The infiltration process in the tissue is a time dependent process. Su, you should make a transient model for the calculation.
What software you use?
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Dear All,
I am working on micro mechanical modeling of metals (X65 grade steel). 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
- In damage evolution: fracture energy. mix-mode ratio 1 and 2
2. I know that for cohesive element , it is important to have the match meshes in boundaries of the surfaces but my question is that is it also important to have match meshes in boundaries when we define surface base cohesive?
I'm looking forward to hearing from you soon.
Thank you,
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Following with great interest.... Thank you so much for sharing this article. Regards, Emad
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In mechanical APDL, combin39,14 elements can be used. But how to use multiple spring elements in ANSYS workbench.
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Dear Sirs,
I would like to find out more precisely whether the 2nd Newton law is valid or not in wide range of masses, accelerations, forces. Particulary I have a question whether the inertial property of body (inertial mass) is able to stop the body for small external forces or not. I have found in the Internet the fresh articles with tests of the 2nd Newton law for small accelerations (10^-10), small forces (10^-13) and SMALL masses (about 1 kg). The articles deal with the question of dark matter and MOND theory in astrophysics.
But I am interested in BIG masses. Could the test be carried out in planetary scale? Maybe for the Moon or asteroids? Or for masses like 1000 kg? Thank you very much for any references.
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- When calculating ephemeris in the most accurate models of EPM and in some DE models, only miserable corrections are obtained from the PPN formalism. The Newtonian gravitation remains in the basement of celestial mechanics and of the GR. To my point of view, and stem from the fact, that geodetic lines in the presence of masses get bent, the Newton’s gravitation law suffers from a fundamental flaw due to violation of the inverse square law, underlying it. Let's try to go down from generalizations to specifics.
For example, discussing the modification of the law of Newton, I will argue that the mass is not an invariant, and the APPARENT gravitational mass depends on the distance to the observer Ma = M (1+ KR), where, for particular body, K = const. To verify the validity of the modified law, one will have to a) recalculate the masses of all celestial bodies in accordance with modified law, and b) get the Shapiro amendment, which will also depend on the (apparent) mass. As a result, using appropriate Shapiro delay values, we may get confirmation of the modified law.
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Dear Sirs,
1, 2, 3 laws of Newtons need closed system (net force is zero). How do we practically realize, create such closed system?
One example. Let us look at a body motion. One can say If the body velocity is constant, e.g. zero then no forces act to it. Is it true? I think no. According to the 1st Newton law the velocity constance is the CONSEQUENCE of F=0.
So are there precise ways to construct closed system? Or all physical theory is just a mean to generate a hypothesis which has more higher probability to be true then other random thought?
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Dear Sir,
To the point how to construct.
Let us take component wise
Forces = Air frictional force if your relative velocity is high like 1m/s, frictional force from ground and touching surfaces, EM forces, Temperature gradients, Electrical Gradients, Gravitational forces.
Maintain constant Temperature that is generally room temperature- If temperature gradients exist then, source of it should be eliminated or considered in the system.
Use Glass material polished with talcum powder.
If any EM material Exist that is taken care by glass itself.
If high velocity Evacuate the chamber i.e. create vacuum.
Cover other surfaces also with talcum powder.
X & Z components are taken care by these.
Y component gravity is left that comes vey expensive.
So to eliminate gravity either use Archemedies Principle or do it simulation if real is not compulsory.
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Could you give references on mass measurement from the 3rd law (with different forces: gravitational, elastic, etc)? E.g. old articles by Saint-Venant.
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Dear Preston,
Thank you very much for your papers
Anatoly
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I'm looking for a good intro for cantilever beam mechanics.
We are given a length and radius of a fixed rod and we apply a force F at the free end.
How can one calculate forces and slopes at each point of the rod?
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Could you please explain more what you want
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I am planning to conduct four-point bending tests on tubes with different lengths and diameters. Do you know of any method to decide the proper loading rate/speed?
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Richard Moran , thanks for your explanation.
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There are shell theories like Love's, Donnell-Vlasov, Sander's,etc genrally used. Which theory is applicable here based on the limiting ratio mentioned above ?
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pls let me know experts opinions
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Hello:
According to professor Brandmark in his article
Osseointegration in skeletal reconstruction and rehabilitation
Rickard Brandmark, MD, PhD; P-I Brandmark, MD, PhD; Björn Rydevik, MD, PhD; Robert R. Myers, PhD
J Rehabil Res DevVol. 38 No. 2, March/April 2001
He gives definition to osseointegration as follows
Definition of Osseointegration Osseointegration was originally defined as a direct structural and functional connection between ordered living bone and the surface of a load-carrying implant (4). It is now said that an implant is regarded as Osseo integrated when there is no progressive relative movement between the implant and the bone with which it has direct contact (2). In practice, this means that in osseointegration there is an anchorage mechanism whereby nonvital components can be reliably and predictably incorporated into living bone and that this anchorage can persist under all normal conditions of loading (5).
Now if you want to know what is happening on the level of histological level then I can refer to Raghavendra S. Jayesh and V. Dhinakarsamy article on osteointegration (listed below as an attachment) where they showed histological steps where osteointegration become a bond between titanium and bone see fig 3 (two parts)osseointegration mechanism .
📷📷
Based on many literature review I read would like to define osteointegration as
A bio-mechanical bond (a new terminology by me ) which explains both the mechanical and biological properties
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I have a ceramic crucible, which is pressed from the sides to hold the weight, for this material, which failure theory can be used from Ansys?
Mohr-Coulomb theory or Max Tensile Theory, which among two will be more accurate for failure prediction?
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Max principle stresses are generally better at predicting failure of brittle materials. The von Mises theory is suitable for predicting yield.
I recommend you check out CARES, a tool specifically developed to analyze ceramic materials: http://www.ceramicreliability.com/index.html
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Is there any procedure to evaluate the viscoelastic coefficient of a material ?
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I think your question lacks a bit of context as the K-V model can be applied to a variety of situations, from actual spring-damper system in mechanical devices to fluids and solids under loads, and more. As you specified that it is for materials, you may want to specify which materials and conditions, or at least the material phase to get a detailed answer.
Nevertheless, I think that from a general standpoint, Mr. Hernández answer's is right. You usually curve fit the model to actual test data. However, the test will depend on the type of material and conditions.
You may want to search the web for ''basic elasticity and viscoelasticity princeton university press'' for a primer on materials mechanics and the relation of the K-V model to actual behaviour (although fitting is not really discussed).
Test standards as ''ASTM D6048—07 (Reapproved 2012) Standard Practice for Stress Relaxation Testing of Raw Rubber, Unvulcanized Rubber Compounds, and Thermoplastic Elastomers1'' may also help you.
Best regards,
Laurent
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You have a cylindrical structure that you want to preserve under impact loading (the force below which the cylindrical structure stays intact is 5kN). How do you design another energy absorbing structure to put between the impactor (which generates a force of 25kN) and the cylindrical structure to make sure that the later stays intact?
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Thanks everyone but my question is more towards what Franco Concli and Jerry Alcone is suggesting.
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Dear RG members,
Why shear fracturing occurs in the rock compression test where no shear stress is applied?
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In the case of uniaxial compression/tension the shear stresses exist in any plane which is not orthogonal (or parallel) to the load direction.
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I am trying to measure the toughness of leaves. I have rigged up a system where I put a leaf on a cube of agar (15g agar per liter water) and drop an empty syringe with a piece of wire (not a needle) through a tube to puncture the leaf. Unfortunately, the weight of the empty syringe is sufficient to penetrate the leaf so I figured a tougher leaf would cause the wire to enter the agar less, thus making a shallower hole. Is there an equation to relate the force required to puncture the leaf to the amount of slowing the leaf exerts on the wire? I also don't know if the difference will be perceptible and perhaps I should find a lighter puncture object
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Hi Alex,
Try checking with with Adam A. Pepi . He has some some work measuring leaf toughness.
Good luck,
Hannah
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mechanical properties
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You can use contact elements for a rigid and deformable body. But this is a more difficult task. More simply - to set the properties of a rigid body an order of magnitude greater than the properties of deformable bodies in your task.
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Dear RG members,
As shown in the attached picture, If the study objects are not rod-shapped, will cracks and fractures occur under gravity?
If crack appear, how to decribe it? how to determine the location of fracture face? and which yiled criteria is applicable in this case?
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only one way, enhance the craked location. make it stronger. such as reinforcing rib.
it will happened at the farthest point from the section center.
for my opinion, the third and fourth theory are both OK for your object. maximum distortional strain energy is more suitable.
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