Questions tagged [solid-mechanics]

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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
19 votes
3 answers
12k views

Why and how is sound produced when two objects hit each other?

When two objects collide and undergo a partially inelastic collision (so every one we experience in every-day life), they rebound to a certain degree, but kinetic energy is not conserved. Thus, the ...
usumdelphini's user avatar
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16 votes
4 answers
25k views

Hollow shaft vs. Solid shaft: Which one's more resistant to torsion?

I recall being told once that hollow rods/shafts tend to resist torsion more than solid rods/shafts...but I wasn't told why this is the case. Now that I'm a little older, running this "fact" through ...
Alan's user avatar
  • 289
13 votes
3 answers
2k views

Continuum limit for solid mechanics

Is there a rigorous derivation of the limits for continuum properties in solid mechanics? For instance, the stress-strain relationship may be linear for large samples (the slope being the Young's ...
tpg2114's user avatar
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12 votes
1 answer
987 views

Why doesn't a bus blow due to internal pressure?

When one travels in a bus, if he's sitting at any window, he will feel that the air is coming inside. If someone is standing at the open door of the bus, he'll also feel that the air is coming inside....
user24503's user avatar
  • 121
12 votes
2 answers
2k views

Is Young's Modulus a Lorentz Scalar?

If a spring is at rest and lies along $X$ axis in a frame $O$ with a spring constant $k_{0}$ then its spring constant in a frame $O'$ which is moving with a speed $v$ at an angle $\theta$ with the $X$ ...
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10 votes
6 answers
25k views

Why rubber is incompressible material?

Why rubber is incompressible material? I know its Poisson's ratio is nearing to 0.5. So I don't understand physically, what it means by 0.5 Poisson's ratio and incompressibility. When I tried ...
user3705273's user avatar
9 votes
3 answers
437 views

Is there any dynamical reason for the winter solstice to happen close to the perihelion?

When the winter solstice arrives, the angular momentum of the Earth, its orbital angular momentum and its radius vector with the orbital focus in the Sun are in the same plane. This happens quite ...
Eduardo Guerras Valera's user avatar
8 votes
3 answers
304 views

Is it possible to reassemble a perfectly cleaved crystalline solid?

This is a purely theoretical question about "perfect" solids under "perfect" conditions. Assume you have a crystalline solid with a perfect crystal lattice (i.e. no defects). Let's imagine a cube of ...
Kevin H. Patterson's user avatar
8 votes
2 answers
2k views

Why are springs spiral-shaped? [duplicate]

I've had this question on my mind for quite a while and looking at the web, I couldn't find an answer to this question. I've had a lot of physics experiments involving springs, unintentionally ...
user avatar
8 votes
1 answer
2k views

Is there a solid material with low acoustic impedance and low attenuation coefficient?

Is there a solid material with both a low acoustic impedance (specifically, an acoustic impedance as close as possible to that of the air) as well as low attenuation? In other words, is there a ...
The Riddler's user avatar
7 votes
4 answers
457 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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7 votes
1 answer
758 views

Why do ribbons curl when we stroke them with scissors?

I have recently learnt how to make quilling swirls [also called paper filigree] ,one of the methods to curl the paper strips is to quickly run your fingernail on the underside of the strip you want to ...
Amarylis Vaselaar's user avatar
6 votes
4 answers
9k views

Does zero strain always imply zero stress?

In solid mechanics, can I always assume that if an object undergoes no strain, then no stress is applied to it? I think it's true only because I can't seem to find a counter-example.
Paul's user avatar
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6 votes
2 answers
3k views

Why plane stress condition is taken for thin plates

Why plane stress is taken for thin plates? It says in the books that the stress variation is small for thin components and is close to zero. Why is that so? Also why stress at free surface is zero? (...
irtiza's user avatar
  • 61
6 votes
5 answers
474 views

General plane motion and freely floating rigid body

Consider a rigid rectangular plate of length $l$, width $w$ and thickness $t$ which is at rest and is floating freely in space (no gravity). The center of the plate is at $O_L$ with respect to global ...
unfinished_sentenc's user avatar
6 votes
0 answers
270 views

Is there a scale at which all solids can be treated as fluids?

I was answering an Earth Science SE question that involved the reasons why Earth has an equatorial bulge, and wanted to make an offhand comment such as "Real planetary constituents aren't this strong; ...
Spencer's user avatar
  • 163
5 votes
2 answers
7k views

Question regarding thermal expansion of a bi-metallic strip

I was reading about bi-metallic strips and came to know that on heating it forms an arc like shape. I also read a sentence that said the radius of such an arc can also be calculated which will be ...
Yami Kanashi's user avatar
5 votes
2 answers
988 views

Intuition for Stress and the Cauchy Stress Tensor

I'm struggling to get an intuitive understanding of what exactly Stress is, particularly the "direction" associated with it. In the case of a 1 dimensional bar with just uniaxial loading, ...
QED's user avatar
  • 303
4 votes
1 answer
231 views

Why isn't there a "parallel" Pressure as there is a parallel or shear Stress?

I had this question while I was reading the differences between pressure and stress. As I have read: Pressure is the intensity of external forces acting on a point, and it always act normal to the ...
user avatar
4 votes
2 answers
273 views

Interpretation of Hooke's Law

I often see people interpreting Hooke's Law $σ=Eε$ as, "The deformation $ε$ that occurs when you subject a material to a stress $σ$." This makes it sound like stress is an external ...
silverbackgorilla's user avatar
4 votes
2 answers
353 views

Why is it harder to situp on solid floor?

When I situp on solid floor it is harder for me to lift my body upwards versus on a soft/foamy floor which I can do a lot.
Rod_Algonquin's user avatar
4 votes
1 answer
845 views

Why is the continuity equation hardly used in solid mechanics when it is essential in fluid mechanics?

For any continuum, fluid or solid, we can express mass conservation through the continuity equation $$\frac{\partial \rho}{\partial t} + \nabla \cdot (\rho \mathbf{v}) = 0 ,$$ where $\rho$ is density ...
Erlend Magnus Viggen's user avatar
4 votes
1 answer
2k views

Hookes law and objective stress rates

Often, in papers presenting updated Lagrangian simulation methods for solid dynamics, the following procedure for updating the (Cauchy) stress tensor is presented: First, the Cauchy stress tensor is ...
Matthias's user avatar
  • 141
4 votes
1 answer
82 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
4 votes
1 answer
41 views

Why does squashed clay 'hug' the press rather than spreading out?

In this demonstration a piece of clay (or clay-like material) is squashed under a press. The lump of clay initially spreads out under the ram of the press. But once it reaches the edge of the ram ...
StayOnTarget's user avatar
4 votes
1 answer
283 views

Is it a law of physics that all machines will break?

The question sounds kinda dumb when I say it out loud but at the same time I'm very curious. When things break, is it solely due to an intrinsic design flaw or is it due to entropy? And is the ...
user3256725's user avatar
4 votes
1 answer
1k views

Wall stress of a hexagonal pressure vessel

Problem: I want to calculate the stress in the walls of a hexagonal pressure vessel but I can't manage to get coherent results. For long vessels, cylinders are supposed to have the lowest hoop stress ...
user42875's user avatar
  • 145
4 votes
3 answers
248 views

Why solid objects create a sound if you tear them apart?

For example, if you are strong enough to tear apart a piece of plastic - it will make a distinctive sound. If you break it - it too makes a sound. Even if you tear apart paper - it makes sound. But ...
Romanov Roman's user avatar
4 votes
1 answer
671 views

Why does sawing action increase the effectiveness of cutting knives?

From practical experience, it's obvious that a sharp non-serrated knife will cut items with more ease if the user attempts a sawing motion. The intuitive reasoning for how a non-serrated knife cuts -...
CoilKid's user avatar
  • 1,334
4 votes
2 answers
5k views

Most rigid materials [closed]

Ordinary web searches are not turning up lists of the most rigid materials for me. I am interesting in finding out the relative rigidity of commonly available materials and how to measure that ...
Ambrose Swasey's user avatar
4 votes
1 answer
406 views

How to write classical dynamics of solids in tensor form (relation of stiffness and viscosity tensor)?

This is a question about dynamics. If I have understood correctly there should be a tensor that describes the dynamics of a (solid?) body (= viscosity ?). I mean, tensor that includes the time ...
Juha's user avatar
  • 800
4 votes
0 answers
124 views

Existence of solid mechanics problems that cannot be solved through Lax-Milgram approaches

Very often, solid mechanicians employ finite-element analyses to solve problems in linear solid mechanics. This approach is guaranteed to work because the Lax-Milgram theorem, along with some ...
aghostinthefigures's user avatar
4 votes
3 answers
781 views

True strain, engineering strain, strain gauges

I've been somewhat confused over the concepts of true and engineering strain, and I just want to see if I am understanding this correctly. Let us denote true and engineering strain as $\epsilon_t$ ...
anonuser01's user avatar
3 votes
4 answers
747 views

Can we write "Normal force" as a function of underlying surface's intrinsic properties?

We usually tend to use Newton's second law for finding equations relating the forces being applied on the (not rotating) rigid body located at a plane surface and then calculate "Normal force" by ...
Hamed.Begloo's user avatar
3 votes
1 answer
19k views

How thick does steel have to be to be able to withstand 300 bar (sphere)

How thick does the material in a sphere have to be to withstand the (inner)pressure of 300 bar if the material is steel? (With an inner-radius of 2cm) Atmosphere pressure = same as 0 meter above sea ...
Harry Svensson's user avatar
3 votes
1 answer
392 views

Equivalence of turbulence in solid materials

The governing equations for a fluid and a solid are effectively the same and many times analysis can be done for a solid using the Navier-Stokes equations with the equation of state and/or the stress ...
tpg2114's user avatar
  • 16.5k
3 votes
1 answer
196 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
3 votes
1 answer
4k views

Limits of Poisson's ratio in isotropic solid

For an isotropic solid, Poisson's ratio can be expressed in terms of stiffness constants as: $$\sigma = \frac{c_{11} - 2c_{44}}{2c_{11} - 2c_{44}}$$ Alternatively we may express Poisson's ratio in ...
user12277's user avatar
  • 341
3 votes
3 answers
6k views

Interpretation of Lamé’s parameters in solid mechanics

I think I have a pretty good understanding of the physical interpretation of Young's modulus $E$ and Poisson’s ratio $\nu$ in solid mechanics. However, I often find in mathematical papers that the ...
Paul's user avatar
  • 683
3 votes
2 answers
4k views

Why is the partial derivative of strain energy function with respect to strain equal to stress

In Elasticity, we have a strain energy function , $W$, that is a function of strain tensor, $E$. Then the cauchy stress tensor, $T$ can be determined by: $$T_{ij}=\frac{\partial W}{\partial E_{ij}} \...
Mike James Johnson's user avatar
3 votes
1 answer
1k views

von Mises yield criterion when all 3 principal stresses are equal and in tension

Based on the von Mises yield criterion, a material begins to yield at a point when the state of stress at that point is such that the scalar known as the von Mises stress, exceeds the yield strength ...
rrkkass's user avatar
  • 75
3 votes
2 answers
697 views

Question regarding bending of beams (solid mechanics)

I'm still in High-school, and we've just finished a chapter on solid-mechanics. A scenario we were supplied with by our teacher, involves a cuboidal beam supported at two ends, like this: Now if a ...
Alan's user avatar
  • 289
3 votes
1 answer
5k views

How to determine plastic strain rate

Equivalent plastic strain rate is defined as $$ \dot{\bar{\epsilon}}=\sqrt{\frac{2}{3}\dot{\epsilon_{ij}}^{p}\dot{\epsilon_{ij}}^{p} } $$ Where, $ \dot{\bar{\epsilon}}$ is equivalent plastic strain ...
343_458's user avatar
  • 135
3 votes
2 answers
1k views

How does stress change through a bar that sharply increases in diameter?

I am looking to analyse the stress through the following bar: The bar is of circular cross section, homogeneous in material, that is of a certain diameter on one half, and a large diameter on the ...
Involute's user avatar
  • 1,931
3 votes
2 answers
1k views

Is there a way to calculate strain energy based on stress and deformation gradient?

We know that we can obtain stress from strain energy density and deformation gradient, for example: $$\mathbf P=\frac{\partial W}{\partial \mathbf F}$$ However, is there a way to calculate $W$ from $...
Shawn Wang's user avatar
3 votes
1 answer
11k views

Materials with Zero Poisson Ratio

Poisson's ratio is defined as negative ratio between transverse and axial strain. So, a material with zero poisson ratio must necessarily exhibit no transverse strain. After checking the wikipedia, ...
Paul's user avatar
  • 683
3 votes
1 answer
5k views

Formulas for compressibility of solids

I am taking a course in mechanics this semester, as well as a course in reservoir physics. Both courses have sections devoted to pressure/compressibility of solids, but the formulas look slightly ...
user12277's user avatar
  • 341
3 votes
1 answer
540 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
3 votes
1 answer
700 views

Is it possible to use the Navier-Stokes equation for solid simulation?

I had a PhD interview yesterday. One of the faculty asked me if it is possible to use a modified version of the Navier-Stokes equation for solid simulation, knowing that both are derived from Newton's ...
Prakhar Sharma's user avatar

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