Questions tagged [stiffness]

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

I need to complete the 3D stiffness matrix of steel concrete composite columns under all kinds of stresses (axial and rotational as shown in the image below). So because the section is a Square Hollow ...
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0 votes
2 answers
62 views

Sign Convention for Energy Methods in Vibration Analysis

Find the equivalent spring stiffness of the system below. I was able to solve it using Newton's second law and got the result below. $$ k_{eq} = \frac{mgl}{2} - \frac{k_1 l^2}{16} - k_2 l^2$$ However,...
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3 answers
130 views

What is the difference between Hooke's Law and Young's Modulus?

In the elastic region where stress is proportional to strain up to elastic limit which is we call Young's Modulus (E). My question is if that is E, then what is Hooke's Law (K=F/x spring stiffness). I ...
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0 votes
2 answers
61 views

Should the stiffness of this cantilever beam be different for these two conditions?

So, I was just doing some Finite Element Analysis (FEA) to figure out what would be the effect on the stiffness of a cantilever beam if another beam is attached to it on its free end. Below shows the ...
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-1 votes
2 answers
68 views

How can I find stiffness of a steel coil spring used in dump trucks?

How can I find stiffness of a steel coil spring used in dump trucks? Here is the data of the question. Length of spring unloaded = 220mm Outer Diameter = 27mm Inner Diameter = 15mm Wire Diameter = 6mm ...
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1 vote
3 answers
2k views

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

Stiffness (F=Kx) is the extent to which an object resists deformation in response to an applied force. Elastic Modulus (E=Stress/Strain) is a quantity that measures an object or substance's resistance ...
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7 votes
5 answers
998 views

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

Can anyone just tell me that why doesn't a jumping rope, or any other kind of rope, have any bending stiffness? If I hold one end of the rope in my hand, the rest of the rope will just fall. It won't ...
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0 votes
1 answer
55 views

Should a stiffener be hatched

In my course it's preferred not to hatch ribs and webs so should I consider a stiffener like them and not hatch it or is it different and why ?
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2 votes
3 answers
943 views

Brittle = highly stiff but not very strong

I was trying to imagine materials undergoing collisions, and thought about materials that do not deform at all. Naturally this is an idealization that does not exist in reality but, if it did, I ...
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0 votes
1 answer
79 views

Will the second beam have higher or lower stiffness in X direction than the first beam?

Attached is a picture of two beams. The second beam has exactly the same properties and dimensions as the first one, but is rotated, say, by 45 degrees. I want to know if the second beam will have ...
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0 votes
1 answer
32 views

Ways to stiffen a HSS profile?

I have an issue with a post that’s deflecting a little bit too much. Picture a 10 foot HSS c-channel section, used vertically as a post. Web/flange 4.5 x 1.75 @ 3/16 thick. Clients (friends) insisted ...
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47 views

Stiffness of spring pendulum from position, velocity, and acceleration

I'm working on a problem for which I have an external tool that integrates the equations of motion of a complex 'pendulum-like' mechanism (multiple beams, torsion springs and dampers, actuation, etc., ...
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0 answers
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On rectangular section beam properties of plate stiffeners

I am trying to understand the expression of the vertical dynamic stiffness $K_T$ and the rotational dynamic stiffness $K_r$ which appears in this paper where they consider a semi-infinite plate ...
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3 votes
0 answers
29 views

How quadrilateral elements represented in most FEA solvers for structural mechanics problems?

How quadrilateral elements represented in most FEA solvers for structural mechanics problems? I know that Nastran-95 represent quadrilaterals for membrane and bending elements as a set of triangles: ...
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2 votes
1 answer
192 views

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

As the title of this post says, how do the contraints increase the stiffness. For example, I was doing an exercise where I had to calculate the deflection on a rubber block with and without deflection ...
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1 vote
3 answers
115 views

Axially loaded member with a spring / Mechanic of Materials

i've been struggling with this problem i made up. It is about a cylindrical copper member (diameter $d=20$ mm and length $L=250$ mm) with a spring (stiffness $k=166,5$ kN/mm) fixed on a wall, as the ...
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1 vote
3 answers
219 views

How to measure the stiffness of a rectangular beam, and compare it to a triangular beam?

I'm an amateur at engineering, working more on musical instruments, and I'm often in confusion regarding what exactly constitutes stiffness of a beam for a load applied on it so it could resist ...
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1 vote
1 answer
201 views

Bending stiffness of composite shaft

What is the method to compute the effective bending stiffness "EI" of a composite structure, in this case a shaft (as seen below). The shaft is hollow with outer radius $r_{o}$, inner radius ...
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1 vote
1 answer
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Database for stiffness matrix? [closed]

I have searched everywhere for the stiffness matrix of GFRP, but there isn't a single paper or site that experimented the full matrix. Is there any sort of database for the stiffness matrix of many ...
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3 votes
0 answers
35 views

How do FE solvers solve the case of panel buckling under pure shear?

How do FE solvers solve the case of panel buckling under pure shear? The main problem is that global matrix of initial stess is singular in that case. One method is to apply some forces that shear is ...
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1 vote
1 answer
96 views

Solving for stiffness matrix numerically by a set of measurements

Is it in general possible when you have a mechanical structure (in this case I am referring to the structure in this post) and you want to determine the global stiffness matrix of this structure, to ...
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4 votes
2 answers
686 views

FEM - is symmetry a boundary condition?

In FEM is symmetry technically a boundary condition? For example using the FEM on a symmetrically loaded and supported beam. The FEM can be simplified by using symmetry. However, is this symmetry ...
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4 votes
2 answers
1k views

Degrees of freedom of an internal hinge in plane beam?

What are the degrees of freedom of an internal hinge in a plane beam? I understand that the bending moment=0, does this mean there is no slope either? Or does it have both degrees of freedom of ...
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  • 253
1 vote
1 answer
51 views

Looking for thin flexible and strong material

I have a project in which I have to use a up to 2.5mm diameter needle with a 90 degree (L shape) angle similar than the one in the following picture: I say similar because there is only the tip of ...
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2 votes
2 answers
4k views

Stiffness of a cantilever beam

I am working on calculating the stiffness of a cantilever beam by applying a distributed load. I wanted to ask if the distribution of the load on the beam effects its stiffness. For eg., if I apply a ...
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4 votes
4 answers
6k views

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

My question may sound silly as it’s mainly good sense but I may be mixing things up. Let’s consider a flexible cantilever beam of a given length and material is fixed at one end and free at the other ...
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2 votes
1 answer
179 views

Stiffness of highly compressible materials

A foam which I have performed compression tests on shows results similar to the following hysteresis cycle: (Note that the first bend in the graph is not the yield point; the hysteresis cycle returns ...
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2 votes
2 answers
2k views

Determining when bolt will bend

I'm attaching a metal pipe to a metal tube as shown in the below diagram. The bolt is threaded through one wall of the pipe and does not pass through the opposite wall of the pipe, but is tightened to ...
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1 vote
2 answers
169 views

Increasing the stiffnes of a structure by adding stiffener, but at the same time reducing main surface thickness

Let's say I'm designing a table surface which has to be stiff, rigid, but at the same time, not too heavy. It is rectangular in shape and ratio of length:width is quite large. It is only supported on ...
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1 vote
1 answer
61 views

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

I have a dynamic mechanical system of the form: $$\mathbf{M{\ddot q}+{\Omega_c}G{\dot q}+{Kq}=F(t)}$$ and I need to introduce some uncertainty for the $K$ parameter, which is a symetric matrix of $q$ ...
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  • 399
1 vote
1 answer
171 views

Beam stiffness matrix with sliding end release in arbitrary angle

I know how to get the stiffness matrix of a beam with any type of end releases (hinges and rollers) by applying Guyan reduction (static condensation) to the beam stiffness matrix in local axes. ...
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3 votes
0 answers
101 views

What is the deflection of planet-ring Gear Mesh along the pressure line and the position of the Plant gear?

For a Sun-Planet mesh in a planetary gear train, there will be a deflection $\delta_{sn}=\delta_{s}-\delta_{n}$ along the pressure line and the position of the planet will be determined by $\psi_{n}$, ...
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  • 399
1 vote
1 answer
168 views

Asymettric stiffness matrix for a generator-gearbox-turbine system

I need to model the system in figure, where turbine, shaft1 and gear1 are a unique rigid body, while shaft2 can be modeled like a torsional spring. Using as coordinates Theta1, clockwise angular ...
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5 votes
2 answers
435 views

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

I'm assuming here that all materials will have a change in elasticity due to thermal expansion/contraction and a resultant reduction/increase in the strength of the bonds of the atoms leading to a ...
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1 vote
2 answers
217 views

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

I cannot wrap my head around this. I have made two simple models, a triangular (or curved or arched) beam that is pin ended and has a single point load of 1N downwards at it's center, and a flat beam ...
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3 votes
1 answer
2k views

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

I have a structure which is essentially a curved beam (not an arch or anything simple) which I have modeled in microstran/spacegass. It looks something like this: Or for something more simple, ...
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  • 176
0 votes
1 answer
5k views

Convert translational stiffness to rotational stiffness of a screw

I have the formula for the translational stiffness which is : However, what I would like to find is the rotational stiffness. Is there any formulas to convert from one to an other knowing the pitch ...
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2 votes
0 answers
2k views

Stiffness of members in a bolted joint

I'm trying to calculate the safety factor against separation of members in a design that looks like this: I know how to find the bolt and cylinder stiffness, but I don't know how to find the ...
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7 votes
1 answer
140 views

Elasticity of a drilled plate

If I take a large thin plate and I uniformly drill a very large number of holes (diameter "d") very close together (minimum spacing "s"), what will be the stiffness of this new plate? When I say "...
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4 votes
2 answers
105 views

Dominant parameters in the dynamical response of a linear oscillator

I am working with a very simple 3-DOF damped LTI spring-mass system. As an exercise I am altering two parameters simultaneously (stiffness and damping coefficients connecting mass 1 to mass 2) to see ...
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5 votes
1 answer
868 views

What are the elastic constants for tetragonal zirconia polycrystal (TZP)?

I have six known elastic constants of TZP. What is the relationship between the known and the unknown constants? Known constants (GPa): $c_{11}=327\\ c_{12}=100\\ c_{13}=62\\ c_{33}=264\\ c_{44}=...
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20 votes
3 answers
35k views

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

I have a 2 mm thick steel plate which is 300 mm long and 30 mm wide, supported at either end. It supports a weight-bearing wheel that can roll along the plate. It currently supports the maximum weight ...
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