Composite FEM Lab-work

Transcription

1 Composite FEM Lab-work You may perform these exercises in groups of max 2 persons. You may also between exercise 5 and 6. Be critical on the results obtained! Exercise 1. Open the file exercise1.inp in a simple text editor (notepad, wordpad) Read the file carefully and draw for yourself the element, its properties and the loading imposed. Which results would you expect? Fill the result expected, or as found later in Ansys, in the next table: Expected Displacement () Stresses (MPa) u x u y u z σ x σ y σ z Ansys the file exercise1.inp. What is the x-displacement? Nodal Solution Ux What is the y-displacement? And the z-displacement? Is this what you expected? What are the stresses? Element Solution Sx, Sy, Sxy, Sz Check the MIN and MAX values next to the graph or use the List Results option in the Postprocessor toolbar Why are the stresses constant? Can you explain / reproduce these values? Close the post-processor and wipe the information from the memory by typing /clear in the command line. 1

2 Exercise 2. Open the file exercise2.inp in a simple text editor (notepad, wordpad) Read the file carefully and draw for yourself the element, its properties and the loading imposed. Which results would you expect? Expected Displacement () Stresses (MPa) u x u y u z σ x σ y σ z Ansys the file exercise2.inp. Activate the Pan-Zoom-Rotate screen in the PlotCtrls list. If you activate the Dynamic Mode, you can rotate the element with the right mouse button. Use Fit to resize your element. What is the x-displacement? Nodal Solution Ux What is the y-displacement? And the z-displacement? Is this what you expected? What are the stresses? Element Solution Sx, Sy, Sxy, Sz Check the MIN and MAX values next to the graph or use the List Results option in the Postprocessor toolbar Why are the stresses constant? Can you explain / reproduce these values? Can you deduct the Poisson's ratios from the FE results? Now perform the same exercise transverse to the fibres, and show that the FE results correspond with the values of E2 and nu23 in the input-file. 2

3 You can either adapt the text-file or use the Ansys GUI in the preprocessing and/or solution mode. Exercise 3. Arbitrary fibre orientations cannot be used in the elements used in the first two exercises. Why not? Which terms are missing? The SOLID46 element allows the user to define multiple layers through the thickness and to define the orientation for each of the layers by means of Real Constants. The exercise3.inp file gives an example for a single layer. Read the input-file and execute it. Confirm that the results are equal to those obtained previously. Now it is far easier to perform the last task in exercise 2. Change the orientation in the input-file, re-run your simulation and compare your results. Can you deduct E2 and nu23? Now change the orientation to 45 deg. Sketch for yourself the expected deformed element. Re-run the simulation. Does the result confirm your ideas? If not: why? Correct the input file. How can the shear/extension coupling terms be determined from an FE simulation like this? Exercise 5. Open the file exercise5.inp in a simple text editor (notepad, wordpad) This file consider a simply supported [0/90]s beam, modeled with PLANE42 Plane strain elements. Read the file carefully and draw for yourself the geometry, its properties and the loading imposed. the file exercise5.inp. What is the force induced by the deflection (the force given by Ansys is here in N/m) List Results Nodal loads Fy Calculate this force using simple theory principle: 3

4 48δ B F = 3 d L 11 The bending compliance d 11 can be calculated using LAP (start from the desktop) Compare the force calculated with the FEM prediction. Repeat these two calculations with thicker beams Layer amount d 11CLT (1/Nm) 2.63E-01 F (N) 14.6 F FEM (N/m) 1456 F FEM (N) diff FEM / CLT (%) -0.3 What do you expect (qualitatively)? Exercise 6. In this exercise, an attempt is made to evaluate the thermal residual stresses in the matrix around a fibre, i.e. on the micro level. Two cases are taken into consideration: a- Stresses transverse to the fibres in a unidirectional Carbon-PEI layer, due to cooling down from the glass transition temperature T g down to room temperature. b- Stresses transverse to the fibres in a cross-ply [0/90]s laminate based on the same layer as in a-, and sue to the same temperature difference. A model is built on the assumption that the fibres are homogenously stacked in a square packing. Also the fibre-matrix interface is assumed as a first approximation to guarantee a good adhesion between fibre and matrix. Open the file exercise6.inp. Draw the geometry and observe the symmetry boundary conditions chosen in accordance to the square packing assumption. The input file as given performs the FE calculations for the first step, called load step 1. A critical issue for the matrix used is the value of the von Mises stresses, which should be compared to the yield stress of the PEI matrix (around 90MPa). Exceeding this stress will induce yielding in the matrix, possible craze forming and eventually crack initiation. Visualise these stresses for different fibre volume fractions, and comment on the possibility of inducing yielding of the matrix. Using the same geometry, apply a second load step simulating the situation b-, i.e. in a cross-ply laminate. The results obtained from this second load step can be found in the post processor, in the menu read results. Comment on the occurring von Mises stresses as a function of the fibre volume fraction. 4

5 Tip: for this last step, it is possible to apply the classical lamination theory to calculate the loading necessary on the FEM geometry. 5