Skip to main content
18 votes
Accepted

Why does a jumping rope have no bending stiffness and compression stiffness?

TL;DR: The bending and compression (buckling) stiffness is so small because the second moment of area of the fibres is small. Bending stiffness It does have a bending stiffness however it is really ...
NMech's user avatar
  • 24.4k
11 votes

Brittle = highly stiff but not very strong

IMHO there is an "misuse" of the words brittle/strong/stiff that the OP is using. My interpretation of brittle has to do with sudden failure during testing with little to none plastic ...
NMech's user avatar
  • 24.4k
8 votes
Accepted

Stiffness of a cantilever beam

Stiffness is a murky term frequently used ambiguously in engineering. However, the most common definition of stiffness is the product of a beam's Young's Modulus $E$ (which is a function of its ...
Wasabi's user avatar
  • 13.1k
7 votes
Accepted

How do the constraints imposed on a material increase the stiffness?

Let me see if I understood it correctly: You have a rubber block under a uniaxial load (compression or tension). That block may or may not be constrained on one pair of sides (the load is applied ...
Wasabi's user avatar
  • 13.1k
6 votes

Why does a simple pin-ended triangular (arched/curved) beam deflect more due to secondary effects (non-linear analysis)?

Play around with a simple version of this structure, made from a sheet of paper fixed in a slight curve, and see what happens when you apply a load to the mid point. If the first example, any ...
alephzero's user avatar
  • 12.5k
6 votes

Brittle = highly stiff but not very strong

These are some great questions to get started thinking about the field of material science! Most of these properties are imao explained very well by looking at a Stress vs strain graph of a material ...
Aaron's user avatar
  • 161
5 votes
Accepted

Degrees of freedom of an internal hinge in plane beam?

Let's start talking not about hinges, but supports. Specifically, why do supports generate the forces (including bending moments, if applicable) they do (or don't)? Think of a simply supported beam ...
Wasabi's user avatar
  • 13.1k
5 votes
Accepted

FEM - is symmetry a boundary condition?

The symmetry itself is not a boundary condition. It is a property of your system which means that both the geometry and the load are symmetric with respect to an axis or a plane. It allows to reduce ...
ClariB's user avatar
  • 174
4 votes

How does stiffness/rigidity affect the bending moment of a beam

There are two basic types of structure. Statically determinate structures are those where you can calculate the forces at the restraints without knowing anything about the flexibility of the ...
alephzero's user avatar
  • 12.5k
4 votes
Accepted

Solving for stiffness matrix numerically by a set of measurements

This is feasible and can be used to modify a theoretical stiffness matrix calculated by the Finite Element method to match experimental results more accurately. The FE model can then be used to ...
alephzero's user avatar
  • 12.5k
4 votes

Why does a jumping rope have no bending stiffness and compression stiffness?

Having low stiffness is part of the specification of a rope. It would be far cheaper to obtain the same tensile strength with a solid rod. Creating and manipulating multiple strands is expensive. It ...
Neil_UK's user avatar
  • 405
3 votes

FEM - is symmetry a boundary condition?

Symmetry is used to reduce the size of the object and therefore the mesh or allow more mesh to represent that reduced object. So the “cut plane” of symmetry is not a boundary where the material ...
Solar Mike's user avatar
  • 15.9k
3 votes

Degrees of freedom of an internal hinge in plane beam?

You seem to be mixing up the conditions on the forces and moments acting across the hinge, and the displacements and slopes there. There is no bending moment transmitted across the hinge, but there ...
alephzero's user avatar
  • 12.5k
3 votes

Stiffness of highly compressible materials

Material science can almost always be broken down into "generally useful" and "specifically useful". The link in the comments demonstrates a commonly used statistic that describes behavior of foams ...
Mark's user avatar
  • 5,333
3 votes

How does stiffness/rigidity affect the bending moment of a beam

About the 2nd question after you read the answers: Actually it's the other way around. Imagine a load on your beam. The integration of the loading is the shear force. The integration of the shear ...
Apostolos Grammatopoulos's user avatar
3 votes

How does stiffness/rigidity affect the bending moment of a beam

As mentioned by other answers, when dealing with a statically determinate structure, the stiffness of each element is irrelevant when calculating the bending moment, but a key variable when ...
Wasabi's user avatar
  • 13.1k
3 votes

How much does the elasticity (Young's Modulus) of concrete and asphalt change with ambient temperature?

For concrete and asphalt, you would be more interested in the properties of creep, which is always a function of temperature. For example, there is an entire wikipedia page about this at this time, ...
Mark's user avatar
  • 5,333
3 votes

Why does a simple pin-ended triangular (arched/curved) beam deflect more due to secondary effects (non-linear analysis)?

The answer of alephzero is spot on. I just want to mention that the arch structure is particularly sensitive to 2nd order effects when it is shallow (say depth to span ratio ~0.1) . It's not ...
minas lemonis's user avatar
3 votes

How to implement a Monte Carlo Simulation for studying uncertainty in dynamic stiffness?

My advice would be to forget about the mathematical theory and start thinking about what the engineering means. It's hard to think of any situation where the stiffness of a sensibly designed structure ...
alephzero's user avatar
  • 12.5k
3 votes

Definition of stiffness for structural dynamics: How would you find the stiffness of an unusual beam directly?

k=F/d is a linear relationship. If you're doing a non-linear analysis, you shouldn't expect a linear response. For this beam, a geometrically non-linear analysis is appropriate if your deflections ...
AndyT's user avatar
  • 3,143
3 votes
Accepted

Convert translational stiffness to rotational stiffness of a screw

The translational stiffness is written as $$ k_l = \frac{A\,E}{\ell},$$ where the stiffness $k_l$ is in $\left[\frac{N}{m}\right]$, the area $A$ is in $\left[m^2\right]$, the young's modulus is in $\...
useless-machine's user avatar
3 votes
Accepted

Should a stiffener be hatched

The standard is that The cylinder part should be hatched but not the rib. So something like the following.
NMech's user avatar
  • 24.4k
3 votes

Difference between Stiffness (K) and Modulus of Elasticity (E)?

"$E$", "$K$", and "hardness", all indicate stiffness but are measured and used in different manners. $E$ - Elastic modulus is defined as the slope of the tangent line to ...
r13's user avatar
  • 8,227
3 votes
Accepted

Transforming the Area of a Hollow Square Section filled with concrete into the equivalent area of just steel

You can simply calculate "equivalent" cross-sectional stiffness values. Note that all non-zero terms of the stiffness matrix depend on one of these values: $EA$ or $EI$. These are the cross-...
Wasabi's user avatar
  • 13.1k
2 votes

How does width and thickness affect the stiffness of steel plate?

As mentioned in other answers, what controls the deflection is the second moment of area, and the easiest way to increase it is increase the thickness. Doubling the thickness would increase the 16 ...
NMech's user avatar
  • 24.4k
2 votes

Stiffness of a cantilever beam

The stiffness of a beam does not change with the loading if the equivalent loads and their points of action on the beam are equal. First lets do the stiffness of the beam under q uniform load. $$\...
kamran's user avatar
  • 22.5k
2 votes

How does stiffness/rigidity affect the bending moment of a beam

In your example the change in the cross section of the beam doesn't have any effect on the end moment even if the beam is a hollow section such as a pipe as long as the ratio of length to depth is ...
kamran's user avatar
  • 22.5k
2 votes
Accepted

Determining when bolt will bend

Assuming that nothing else will give out first, what metric would I use to estimate how much weight it can support before flexing the bolts? Is it "bending stiffness" rather than "shear strength"? ...
Drew_J's user avatar
  • 593
2 votes

Bending stiffness of composite shaft

The bending stiffness will be determined by the second moment of area ($I$). The formula you provide $\int\int r^2 da$ is for the Polar Moment of area ($J_p$), and is valid for torsional problems. ...
NMech's user avatar
  • 24.4k
2 votes

Database for stiffness matrix?

The material has to be tested for each application as the fibre density, weave and number of layers all have effects on the stiffness. This means even each batch may have a variation so exact values ...
Solar Mike's user avatar
  • 15.9k

Only top scored, non community-wiki answers of a minimum length are eligible