Stiffness Definition and 144 Threads

Hi all, I'm wondering if anyone knows of a way to obtain elasticity properties (Ex, Ey, Ez, Gxy, Gxz, Gyz, vxy, vxz, vyz) from the terms of a 6x6 anisotropic stiffness or compliance matrix. I'm looking for a closed form solution, preferably. I would think that there should be a closed form...

Hi all, I'm looking for physical and mathematical explanations for a phenomenon I've noticed when working with rotated material properties relative to an XYZ coordinate system. For certain rotations (~40 to ~50 degrees) about a single axis the S12, S13, or S23 components of the compliance...

Hello. I need help with the following problem: I don't know where to start. I know that the frame can be split up into one symmetric part and one symmetric+assymetric part but i forgot the theory and rules on translation and axis etc. I hope someone can help as I have to hand in the...

Hello, Looking for some advice on increasing bending stiffness of a mild steel 1" x 0.065" round tube. This is for a motorcycle frame and clearance is an issue. There is a fuel tank above and the engine below this top tube (two running parallel) that I wanted to reinforce against bending...

I am going through Shigley's Mechanical Design book and have a quick question on fasteners. Sometimes when calculating the spring rate for a member, you have to multiply the rate by 2, why is this? For instance in this problem http://imgur.com/2ug9AaR When the spring rate is calculated for...

Dear all, I am writing my finite element code for linear elasticity analysis with linear tetrahedral elements. I am not new to the finite element method and my code already works well with element types of triangles, quadrangles in 2D and hexahedrons in 3D but I don't get the correct result...

This problem has a lot of calculations from the beginning so i have skipped to the part i am stuck with and tried to include relevant information, apologies if i have missed anything. Assume all working is correct as i was given the answers. After carrying out the stiffness matrix method I am...

I'm creating a computer implementation to solve planar trusses. And I'm not sure how to check if the truss is solvable or not. Can you help me with that? In my implementation, the trusses are created randomly (needs to be this way), so i get a lot of unstable or indeterminate trusses. I want...

Looking at the Einstein equation, stresses can cause a deformation of space time. This link here https://twitter.com/anilananth/status/339030628181868544 gives a value for the elastic modulus ("stiffness") of spacetime. I think that the value of 10^24GPa must be related to Einstein's...

Hi, When I discuss about gears NVH, the term contact stiffness(Cɣ) comes across very often. It is given with a nominal mean value with its upper and lower fluctuation. I can thus understand that the stiffness varies from the start of mesh till end of mesh reaching the mean value at it's pitch...

Hello every body, I am simulating a 1 dof spring-mass model in ansys workbench. I need to change the stiffness of spring at every substep based on an "if condition". It means that, in every substep, if a specified condition is satisfied, the stiffness will be changed to a defined value. Also...

Hi all. It's been a few years since I've posted here, but it's remained a great go-to resource for me. Any time I have dealt with mechanical vibrations, the fundamental frequency was based on a constant stiffness. However, I have never encountered the subject of finding the fundamental...

Question: Part 1: Below about 80 K the heat capacity at constant volume for hydrogen gas (H2) is 3/2k per molecule, but at higher temperatures the heat capacity increases to 5/2k per molecule due to contributions from rotational energy states. Use these observations to estimate the distance...

Homework Statement Suppose a spring with forces F=k*z. Find the equivalent stiffness of a horizontal spring, where the spring and its horizontal equivalent is separated by theta degrees. The horizontal equivalent presumably will have a force F(x)=k(x)*x Homework Equations F =...

1.How do i derive the stiffness matrix for a beam with nodal linkage? ie the shear force at the first node is 0 but the usual shear and moment resistance is present for the second node. I thouth about solving the problem by just putting the first row of the stiffness matrix as 0 . Am i...

Hi, This is a sample problem from logan finite element method. I have attached the problem and solution given in the book. As per the problem i first derived the stiffness matrix and den putting the boundary conditions started solving for the forces. I am stuck as three forces are unknown but...

Hello, My question is simple, but it does confuse me. I need to know the exact difference between Initial stiffness,post limit stiffness, and secant stiffness in details please Please clarify this on graph if possible Thank you

Hello, I am conducting FE modelling on specimen of steel surrounded by concrete, and i obtain curve which have stiffness similar to experiment(all assume linear behaviour for all materials) but the start of curve is not convenient displacement -0.0071033 0.0123265 0.0310888...

Homework Statement Homework Equations 1-Stiffness matrix? 2-When i am doing the deformation,should i consider stress stiffenning or just solve the problem as is The Attempt at a Solution I tried to form the necessary stiffness matrix but couldn't understand how should i...

Homework Statement A scheme of springs and dampers is given. What is equivalent stiffness and damping? Homework Equations For stiffness in series: keq=ka*kb/(ka+kb) For stiffness in parallel: keq=ka+kb For dampers similarly. The Attempt at a Solution To me it looks like k1 and k2 are in...

I am trying to design a spring given the following measurements: Spring Stiffness is 400N/m or 295 ft lbs Outer Diameter of spring is 0.25 in Free Length is 3 cm or 1.18 in Load is max: 5lbs I am having trouble with: Calculating the Spring Diamter so as the spring is not over damped...

Merely a question concerning elementary calculation of stiffness: I have two rectangular and solid bars made of the same homogeneous material: Bar A is 0.85 cm high and 0.5 cm wide, whereas bar B is 1.0 cm high and 0.425 cm wide – and as both bars have the same cross-section area (of 0.425...

Howdy, If I have the following configuration of nodes: 2---4--6 | \ | /| | \ | / | | \| / | | \/ | 1---3--5 What should the dimensions of my FEM stiffness be? Thanks

What led to relativity is the thought experiment where two people are attached, one to a coil and one to a magnet. It is described at the end of this page . http://www.physics.ucla.edu/demoweb/demomanual/modern_physics/special_relativity/special_relativity.html My question is in the...

stiffness of a single interatomic "spring" PLEASE HELP One mole of tungsten (6 1023 atoms) has a mass of 184 grams, and its density is 19.3 grams per cubic centimeter, so the center-to-center distance between atoms is 2.51 10-10 m. You have a long thin bar of tungsten, 2.5 m long, with a square...

Hallo Engineers, I am a little bit confused here and i need some guidance. Can any of you educate me on how to calculate the Bending and Torsional stiffness of a Hat/Omega stringer attached on a plate to form a fuselage panel?..You can also recommend to me a book where it is clearly described...

Homework Statement I have the following practice problem which is presented as follows: What is the size of the global stiffness matrix K (i.e., Kuu) for the 2-D problem? http://imgur.com/KZec3 (Unsolved) http://imgur.com/piv1J (Solved) Homework Equations The Attempt at a...

As per Maxwell reciprocal theorem, it is valid only for elastic materials and structures indergoing small displacements.That is k12 = k21, kij = kji hence stiffness matrix is symmetric. Howbver, I just have been going through MY OWN written programs for geometric non linear problems and I...

AFAIK, the wood used for aircraft structures should have a specific stiffness, that is specific Young's modulus and bending strength, somewhat higher than aluminium (see attached image). If that is the case, why wood aircrafts are generally more subject to aeroelastic effects compared to...

I'm researching CNTs and am currently describing Graphene as I lead from carbon atoms to nano-tubes. I've come across this: "The force-displacement behavior is interpreted within a framework of nonlinear elastic stress-strain response, and yields second- and third-order elastic stiffnesses...

Homework Statement a machine of mass 100 tonne generates a simple harmonic disturbing force when operating at a speed of 200rpm. to protect the floor and surrounding machinery it is proposed tp mount the machine on helical springs so that the transmissibility ratio is reduced to 0.1 Q1...

Homework Statement What happens to the frequency of oscillation if stiffness increases and why? Homework Equations ? The Attempt at a Solution Frequency increases but trying to figure out why.

stiffness and damping coeficients of a VW Golf Hi! I need information about the VW Golf IV 1.6 16V(2003). I need to estimate and calculate the transfer function of the quarter model car so i need the coeficients of stiffness (K) (N/m) and damping (C) (Ns/m) of the front suspension, its...

I am thinking about building a projector screen out of MDF. Here Down Under the available sizes are: http://www.misterplywood.com.au/products/mdf. Building such a screen will be easier than the normal frame with stretched fabric type, but I am concerned about its long-term flatness. So I thought...

Hi, For an undamped mass, spring system subject to a harmonic force, the equation is: ma+kx=Fsin(ωt) where a=d^2/dx^2 After solving the diff eqns, the steady state amplitude is: X=(F/m)/(ω^2-ω0^2) where ω is the frequency and ω0 is the natural frequency =sqrt(k/m) according to the...

My main question is why we derive the structure matrix for a beam like the attached first picture; we assume the beam on the left on point B has no deflection? While i check this by computer analsysis program and it has an effect. Please explain in details The second question is the...

Guys when i study earthquake , they told me that the column stiffness is 12EI/L3 if column is fixed -fixed and 3EI/L3 if column is pin -fixed, so how they get this, i try to study stiffness Matrix and it gives you big matrix for frames not Only one factor like 12EI/L3 please explain

Hey guys I am looking for the solution to replace the spring in MDOF model with wind stiffness or air stiffness if to build a MDOF model of wind. What I have now is only a wind speed data matrix. Anyone can provide some equations of calculating wind stiffness and some clues maybe...

I am currently working for a Touring Car Team . I have modified the front suspension geometry . Made the roll moment lesser and increased the Roll stiffness . Driver complained that the steering effort has increased considerably in the corners . 1.How does increased roll stiffness increase...

Hi, I have forgotten quite a bit of my vibration studies, so I have a fairly basic question. Essentially, when you want to find the natural frequency of a single dof system, you use ω=√k/m. However, does anyone know a general procedure (not problem-specific) for finding "k" that is applicable to...

I have gone through Beam Element analysis in several books on FEA. 80% of books have a particular Stiffness matrix, while a very small number of books have a matrix which is subtly different in sign. http://www.flickr.com/photos/66943862@N06/7195680680/in/photostream/lightbox Most books have...

Homework Statement I'm unable to calculate the stiffness of the spring. Once, i get the stiffness i'd like to calculate the load required for the defined deflection. Homework Equations - The Attempt at a Solution -

Dear all, I have written a code for structural analysis using the finite element method. For some reason, I directly started with 3D elements ( hexahedron). I used to believe that the code was fine but recently i realized that the results ( deformation, natural frequency,..) strongly depend...

This is not a HW question, but a question that I need help solving. I am having an argument with a co-worker about the solution. There is a 4ft sq sheet of plywood with an 18" wide rubber band stretched across it. To measure the spring constant (stiffness) of the rubber band a 6" diameter...

Stiffness of a single interatomic "spring"? One mole of iron (6 x 10^23 atoms) has a mass of 56 grams, and its density is 7.87 grams per cubic centimeter, so the center-to-center distance between atoms is 2.28 x 10^-10 m. You have a long thin bar of iron, 2.8 m long, with a square cross...

Hi community member, Regarding the book that I'm reading original writer has used Ni = ai + bi*x + ci*y shape function for the formulation of stiffness matrix for thick triangular plates. The writer has not mentioned in the article that the resulting stiffness matrix is required to be...

hi all, Actually I'm looking for little help and kinda confirmation, in order to verify that I understood the logic of construing the stiffness matrix. I got the logic of how to construct the stiff matrix for bending and membranes to some level, although FEM books suggests to simply combine...

hi, I'm studying the book for elasticity theory and I stuck at one of the equation in that book, the stiffness matrix for elements(thin or thick plate) in bending is given in that form ke= t∫∫BT*Db*B*det(J)dζdη+∫∫BT*Ds*B*det(J)dζdη B is the strain matrix(5x12) where the inner...

A 73 kg trampoline artist jumps vertcally upward from the top of a platform with a speed of 4.8 m/s. a) What is his speed as he lands on the trampoline, 2.6 m below his jump off point? Express your answer to 2 significant figures. = 8.6 m/s (already figured out this to be the correct...

So say I have a steel pipe under a torque and an axial load. I want to know whether the axial load has any effect on the twist due to torque. Have one calculation which (perhaps falsely) assumes the pipe is made of lots of axially running "wires" and calculates the torque due to this axial...