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4 votes
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What does a mechanical Josephson Effect look like?

This question is related to my research work in physics concerning the brittle-ductile-transition (BDT) in solid state mechanics, which ended quite some time ago and is summarized in my thesis from ...
thomashennecke's user avatar
-1 votes
1 answer
58 views

Angular Velocity of 3D object rotating in space

For a sphere rotating about z axis, its angular velocity is rate of change of angle of a radius vector in xy plane with x axis or y axis. I understand this clearly. But consider a 3d body which is not ...
Saivardhan Annam's user avatar
4 votes
3 answers
281 views

What is the physical significance of Moment of Ineria about a point vs Moment of Inertia about an axis. In which types of problems we use the former?

I know the mathematical formula of both about an axis and a point. But where exactly we use moment of Inertia about a point. For 2d objects like discs rotating in its own plane, the moment of Inertia ...
Saivardhan Annam's user avatar
11 votes
1 answer
1k views

Why does the cross section of a metal after a hypervelocity impact look like that?

Look at this image of a cross section of a piece of (I assume) metal after a hypervelocity impact: I understand where the crater shape comes from, but what puzzles me is the cavity near the bottom: ...
paulina's user avatar
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0 votes
1 answer
61 views

Rigid body motion (RBM) transformation of interface points between a rigid and an elastic bodies

Above are pictures of a problem in mechanics. An elastic body occupying domain $\Omega$ is supported below with a fixed support and from above with a rigid body. The following calculations aim to ...
user134613's user avatar
0 votes
2 answers
54 views

Why lateral strain occurs when volume is not conserved on applying longitudinal stress?

I first thought that lateral strain occurs to conserve volume on applying longitudinal stress but later I realised that I was wrong. But now I have a confusion that why lateral strain occurs if volume ...
S K's user avatar
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0 answers
24 views

Pushing solid objects by photon exchange

As I understood it, the reason I cannot stick my hand through a metal block is due to the repelling force between electrons in my hand and in the block. QED depicts two electrons repelling with a ...
twmen's user avatar
  • 49
1 vote
2 answers
186 views

Point load distribution inside elastic solid continuum medium in finite elements method

In finite elements method, when point load is applied to a particular node of elastic solid continuum medium (e.g. soil), does it affect nodal forces in the rest of the mesh (i.e. does each node ...
bigmazi's user avatar
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19 votes
1 answer
5k views

Why is paper inelastic but flexible?

Recently I have been studying solid structural mechanics, and one of the points I find really confusing is how elasticity and flexibility are closely intertwined. Consider an Euler-Bernoulli beam, for ...
FLP's user avatar
  • 337
0 votes
3 answers
187 views

Computing Cauchy stress tensor in a static cube of uniform isotropic material

As the title says, I'm interested in explicitly calculating the value of the Cauchy stress tensor in a static (non-moving) cube of some material that has uniform density an is isotropic (e.g. concrete)...
lisyarus's user avatar
  • 166
4 votes
1 answer
105 views

What's the difference between constitutive laws and equation of state?

While defining material properties in finite element modeling, when should we opt for constitutive models, such as Linear Elastic or Neohookean (that relate stresses and strains) over Equation of ...
Anu Tripathi's user avatar
0 votes
2 answers
106 views

Problem in thermal stress equation

I came across this derivation of thermal stress where the strain is given as $\frac { l_0 \alpha t}{l_0}$. However, I believe it should be $\frac { l_0 \alpha t}{l_0(1+\alpha t)}$ to consider the ...
Harjot Dhillon's user avatar
1 vote
1 answer
54 views

In-plane stresses on the surface of a cylinder

The three principal stresses on the surface of a cylinder are the hoop, $\sigma_\theta=\frac{pR}{d}$, longitudinal, $\sigma_z=\frac{pR}{2d}$, and radial, $\sigma_r=-p$, stresses. However, what are the ...
Caesar.tcl's user avatar
1 vote
1 answer
36 views

Infinite deflection on axially compressed beam

With $k$ proportional to the square root of the compression force, an axially loaded (and otherwise unloaded) beam has a deflection following the DE $$ \frac{\partial^4}{\partial x^4}z + k^2\frac{\...
user877329's user avatar
1 vote
1 answer
45 views

Would anyone be able to provide a reference for the equations concerning plane strain and incompressibility?

I've been trying really hard to find a textbook or research paper that mentions the equations I mentioned in my question. Sadly, I haven't had any luck so far. Would it be possible for someone to ...
0 votes
0 answers
30 views

The expression of elastic energy in this paper

Elastic properties of $\rm{Ni_{2}MnGa}$ from first-principles calculations Hello, I am reading a paper investigating the linear elasticity of a crystal. However, I am a little bit confused over the ...
蕭力諶's user avatar
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1 vote
1 answer
107 views

Why is the maximum stress of a uniformly tapered round bar lesser than that of a inverse uniformly tapered round bar?

Given two round bars with uniformly tapering radii, one from a smaller to a larger radius and one from a larger to a smaller radius, the former bar experiences greater maximum stress. Since stress ...
agok1's user avatar
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0 votes
1 answer
140 views

Why are the shear stresses corresponding to adjacent faces of the stress element equal?

I am studying the definition of the stress element from the book Theory of Elasticity from S. Timoshenko and J.N Goodier. In page 3 it is shown that from taking the moment of forces acting on the ...
TheScientist's user avatar
0 votes
1 answer
30 views

Rigid projectile penetrating a solid target at normal incidence

Let's suppose we have an equation that describes the minimum kinetic energy required for a rigid ogival projectile to perforate a target as a function of it's thickness T. Can we use this information ...
John Smith's user avatar
7 votes
4 answers
512 views

Addition of forces on a rigid body instead of a point

When two forces act on a point mass,we add the forces like we usually do and i have no problem understanding that. When the same forces are applied on a rigid body,how are we able to add them the same ...
madness's user avatar
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3 votes
1 answer
255 views

Why does the torsion in a circular bar result in shear stress along the axial direction?

In the case of pure torsion, how does a differential area on cross-section of the cylinder with dx length undergo a shear force that is perpendicular to the cross-section ? I can understand that a ...
raconteur's user avatar
0 votes
1 answer
66 views

Mass conservation in a deformed membrane in cylindrical coordinates

This is clearly an obvious question but here is my issue. Context : We assume an axisymmetric deformation of a membrane, and work with cylindrical coordinates $(r; \phi; y)$. At time $t = 0$ we let $r$...
Waxler's user avatar
  • 109
1 vote
1 answer
34 views

What is the correct formulation of momentum balance for a body of continuum?

What is the correct form of the momentum balance equation for a continuum body $\mathscr{B}$ whose particles are fixed, and occupies volume $V(t)$ at time $t$? \begin{align} &\frac{\mathrm{d}}{\...
Naghi's user avatar
  • 167
1 vote
1 answer
60 views

What is the correct form of the conservation of mass equation?

What is the correct form of the continuity equation for a continuum body $\mathscr{B}$ whose particles are fixed, and occupies volume $V(t)$ at time $t$? \begin{align} &\frac{\mathrm{d}}{\mathrm{...
Naghi's user avatar
  • 167
2 votes
2 answers
574 views

Simulating rigid body collisions in 3d

I have been reading about physics engines and I am confused on how one approaches simulating collision responses. I read about the coefficient of restitution: https://en.wikipedia.org/wiki/...
FourierFlux's user avatar
1 vote
0 answers
55 views

Wave equation in two different forms (2nd order, 1st order): Which of the two should I use and when? [closed]

I am studying elastic waves in solids. Depending on paper or documents, the wave equation is written in two different forms. The first form is in the second order PDE $$ \rho \frac{{{\partial ^2}{\...
ENHorse's user avatar
  • 11
1 vote
1 answer
214 views

Continuum mechanics cauchy stress

I have a question regarding the stress tensors. In a publication I found the following definition: I havnt seen this equation before, and I am wondering how to get there. T is the Cauchy stress, Je ...
Juilette96's user avatar
2 votes
3 answers
268 views

When is the equation $\vec{L}=I\vec{\omega}$ not valid?

When is the equation $\vec{L}=I\vec{\omega}$ not valid? Let me clarify, I've encountered a few problems where the angular momentum you obtained by integrating and the angular momentum you'd obtain by ...
user avatar
2 votes
3 answers
148 views

Do forces act on points or areas?

In a lot of situations we are taught about forces acting on points on solid objects (torque, point particles), and in other cases (axial stresses) we consider them as acting on an 'area', is this ...
user1007028's user avatar
0 votes
1 answer
31 views

Cyclic values inside stress tensor in given configuration

i have majored in mechanical engineering and implemented a fully working FEM-Solver for structural mechanical problems for 2 and 3-dimensional problems. I have lately been working on bringing this to ...
Finn Eggers's user avatar
0 votes
1 answer
366 views

What are the effects of Bravais lattices classification differences in 2D space on the physical properties of the crystals? [closed]

There are five possible distinct Bravais lattices in two-dimensional space. For example, if crystal A is Monoclinic (M) and crystal B is Hexagonal (H), how will the difference in their 2D Bravais ...
Kevin's user avatar
  • 109
1 vote
2 answers
109 views

Movement of a rod submitted to a shifted torque

Suppose I have a rod of mass m initially at rest, for which a torque (F1, F2) is applied at the right side during a brief time $\Delta t$, as in the schema below. The rod is not fixed to anything and ...
MikeTeX's user avatar
  • 487
1 vote
0 answers
50 views

What is the function of air cavity in drums?

I'm trying to understand the function of the air cavity inside drums. I've read that 'The air cavity inside the drum will have a set of resonance frequencies determined by its shape and size. This ...
Aethermimicus's user avatar
3 votes
1 answer
646 views

Is charge carrier density an intrinsic property of a material and is thus constant?

I was studying the equation $$I = nAvq$$ where $n$ = the charge carrier density, $A$ = cross-sectional area of the conductor, $v$ = mean drift velocity of the charge carriers, and $q$ = the charge on ...
Sheraz Malik's user avatar
1 vote
1 answer
350 views

Can we prove the Hooke's law? [duplicate]

I was learning about stress and strain and my text book suddenly mentions about this law so called hooke's law. It states that $$\text{stress}\propto \text{strain}$$ Or, $$ \text{stress}=k \times \...
RAHUL 's user avatar
  • 658
1 vote
1 answer
62 views

Absence of velocity in energy conservation

Here we see a rod at rest hinged about a point. We want to know the angular speed of the rod when it becomes vertical as shown in the figure. The solution which is given in the books goes like this. ...
madness's user avatar
  • 1,179
0 votes
1 answer
43 views

Doubt in derivation of bending of beam, It's about derivatives and intergration

Radius of curvature of the beam in above picture is given as: $$ \frac{1}{R} = \frac{d^2 y}{dx^2}$$ Please help me two points used as steps of a derivation in my book: How was the radius of ...
Sai 's user avatar
  • 71
-1 votes
1 answer
71 views

Why two wires are used in railway overhead equipment? [closed]

While watching the train video's I came across this overhead wires. After searching on internet I found that both catenary and contact wires carry same voltage and connected by vertical wires called ...
mech_duck's user avatar
  • 101
0 votes
3 answers
162 views

Where does the stored potential energy in a bar go, when I reduce the load acting on it?

Consider a deformable bar, fixed at one end and acted upon by a load P (gradually increasing), as shown, through a rigid plate attached to its end. At the end of loading, potential energy is stored in ...
Harshit Rajput's user avatar
0 votes
1 answer
1k views

Stiffness for helical spring under lateral bending force

The stiffness for a helical spring under axial loads is $$k_\text{axial}=\frac{F_\text{axial}}{\delta_{axial}}=\frac{Gd^4}{8n D^3}\, ,$$ where $G$ is the shear modulus, $d$ the wire diameter, $D$ the ...
Narasimham's user avatar
  • 1,032
0 votes
3 answers
437 views

In stress-strain diagrams, why is the dependent axis ($y$) used to represent stress and the independent axis ($x$) to represent strain?

why this convention is used despite the fact that strain is influenced by stress (cause -> stress, effect -> strain)
spacepotato's user avatar
0 votes
1 answer
871 views

Volumetric Strain In a Thin Spherical Pressure Vessel

Consider a thin spherical pressure vessel with a fluid inside at a gauge pressure of P. The normal stress developed in the pressure vessel is given by $$\sigma = \frac{Pd}{4t}$$ where t = thickness , ...
Harshit Rajput's user avatar
0 votes
1 answer
89 views

Interpreting stress at the ends of a bar

Consider a bar loaded in tension by distributed loads applied on its ends as shown in the figure. The stress at any cross section of this bar will be $$\sigma = \frac{P}{A}$$ From what I know about ...
Harshit Rajput's user avatar
1 vote
0 answers
44 views

How can the total torque of a body equal a "torque" at only one point?

I am trying to understand the solution to this problem. Pictured is a rough sketch of a ball in which another, smaller ball of density $\rho_2 > \rho_1$, where $\rho_1$ is the density of the ...
turmur's user avatar
  • 11
0 votes
1 answer
147 views

Which occurs first: stress or strain? [duplicate]

Of stress and strain, which is the cause and which is the effect? Is stress a cause of strain, or is stress an effect of strain, or do they occur together (by applying Newton's third law)?
user avatar
2 votes
1 answer
569 views

Stress in a rigid body

Consider two bars one rigid and the other deformable, acted upon by two equal and opposite point loads P as shown. In either of the cases, if we cut the beam from an imaginary section, then, to bring (...
Harshit Rajput's user avatar
0 votes
1 answer
146 views

How to interpret a differential stress element with differing stress magnitudes on opposite faces?

The element is in equilibrium, but with different magnitudes of stress on opposing faces. What meaning does this have physically? See attached image. Thanks
Garrett's user avatar
0 votes
1 answer
413 views

Why the elastic limit of solid corresponds to a larger strain/extension than the limit of proportionality?

In all the force-extension graphs I saw, the elastic limit corresponds to a larger extension than the limit of proportionality. Is this true for all cases? If so, what are the underlying reasons?
Winniebear's user avatar
1 vote
1 answer
206 views

Stress tensor and equality of normal stresses on opposite faces

Consider a body arbitrarily loaded as shown, At a particular point in the body, I take an element and show all the stresses acting on its faces. To specify a plane I will be using the the axis which ...
Harshit Rajput's user avatar
0 votes
0 answers
102 views

Is it possible to find Coefficient of Restitution without performing experiment? But only using mathematical equations?

I was finding empirical equations to find Coefficient of Restitution (COR) for two solid bodies undergoing collision. Seems like all have used experimentation to find COR. Is there any way to find ...
AJAY SARAF's user avatar

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