# Gregory1991

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1. ## The optimization result is not symmetric for L-shaped structure

Hi, Does anyone have any idea about the above question?
2. ## The optimization result is not symmetric for L-shaped structure

Hi, Prakash, Thanks for your help. I knew pattern grouping may help. However, in my case, the design variables include the left nodes movements, the corner nodes movements and the right nodes movements as shown in the figure. Besides, the left, corner and right nodes moves along z-axis (normal direction) in the local coordinate 1, 2 and 3, respectively. Therefore, the pattern grouping for all nodes of inner part is not possible since the pattern grouping is just suitable for one design variable. Do you know how to solve this problem? Best regards, GUO
3. ## The optimization result is not symmetric for L-shaped structure

Hi guys, I obtained the optimal L-shaped structure using free-shape optimization method. Inner nodes can freely move in thickness direction within a certain range (as shown in figure 1). Minimizing the out-of-plane tensile stress (interlaminar tensile stress) is the objective. The constraints are that maximum load point displacement and total weight are less than or equal to that before optimization. However, in the case of shape change, it is not a symmetric result although the input and loadcase are symmetric (In the attached figure 2). Do you have any idea about the reason? If possible, do you have any idea how to obtain symmetric result? I share the model file and results as follows: 1) Input deck of the free-shape optimization of L-shaped structure: L-shaped_free-shaped optimization.fem 2) Result of the free-shaped optimization: L-shaped_free-shaped optimization_des.h3d Best regards, GUO
4. ## ERROR : TIME STEP LESS OR EQUAL ZERO in the case of Composite layup using RadiossBlock

Hi, George, Thanks for reply. According to your suggestions, some progress have been achieved, however, new problem also occurred. In order to model delamination and save computation time, I created zero thickness 3D element as cohesive element between two layers of composite hollow beam according to However, when submitted to calculate, too many warnings and error ID 760 happened as follows: WARNING : ZERO OR NEGATIVE 3D SOLID VOLUME DESCRIPTION : ZERO OR NEGATIVE VOLUME 3D ELEMENT ID=2031 WITH VOID PROPERTY SET So could you help me to figure it out? Thank you.
5. ## ERROR : TIME STEP LESS OR EQUAL ZERO in the case of Composite layup using RadiossBlock

Hi, George, For the above 2D model, I have solved the problem. Thanks! For using Mat 28, I created 3D model to investigate the fracture behavior of hat-shaped hollow beam subjected to static flexural loading, relevant tensile, compressive and shear nonlinear curves were created. Although I have created /DT/BRICK/CST, the error information “time step less or equal zero” still occurred after several time step when the compressive stress reached to the compressive strength. I searched the forum about the error, but cannot still solve the problem. Please check the model attached here. 3D_t2_full_fracture_mat28_0000.rad 3D_t2_full_fracture_mat28_0001.rad 3D_t2_full_fracture_mat28_0001.out
6. ## Model setup of composite curved structure for delamination fracture behavior

Besides, I checked the keyword /FAIL/LAD_DAMA, the "help" files show that for Quad 2D element, only Mode II and Mode III are available. However, the investigation on Mode I was the focus even though 2D element was used in my case. So does that mean only multiple solid layers can be used to study the Mode I by using /FAIL/LAD_DAMA?
7. ## Model setup of composite curved structure for delamination fracture behavior

Hi, George, Thanks for help. I am afraid that the model you sent to me was not same as what you said, because the layers are modeled using PROP17 and PROP 19 rather than creating plies and laminates. Moreover, I cannot find how to extract damage parameters by using /FAIL/LAD_DAMA in engine files of your model. Of course, if I misunderstand, please point it out. Besides, in my case, which one do you recommend as follows? 1) Layers are modeled using PROP17 and PROP 19. 2) Layers are modeled by creating plies and laminates.
8. ## Model setup of composite curved structure for delamination fracture behavior

Hi, George, I sent the files to you for your information, please check them. Thank you very much.
9. ## Model setup of composite curved structure for delamination fracture behavior

Does anyone help me solve the above problem?
10. ## Model setup of composite curved structure for delamination fracture behavior

Hi, George, Thanks for your suggestions. 1)Imposed velocity was used in the model, but high dynamic effects still occurred. So what should I do? 2)I checked your attachments, however, there is no information about how to extract damage parameters when we used /FAIL/LAD_DAMA keyword. BTW, I cannot find /ANIM/SHELL/IPLY/MAXDA, /ANIM/SHELL/IPLY/DAM keywords in the engine file in Radioss Block 140 which suggested in another post. For Radioss 140, can we extract damage parameters? 3)Besides, /FAIL/LAD_DAMA was also tried, it seems worked, at least for fracture stress, however, the results' animation look very weird. Please see the attachment. I have no idea what happened after delamination, so what should I do?
11. ## Model setup of composite curved structure for delamination fracture behavior

Hi, George, For speed the computation time, I have used /DT/AMS keyword, anyway, I just sent the h3d file to you, please check it. Thanks very much.
12. ## Model setup of composite curved structure for delamination fracture behavior

Hi, George, Thanks for your help. Yes, the loading condition is static one ( 2mm/min) in the experiment, and I set velocity as 20mm/s in the FE model to reduce computation time. I modified my model with /MAT/LAW12 and increase the gap to 0.45 (Correspondingly set Gapmin as 0.4). The element orientation is correct, and I solve the problem (maximum Stress Z is not equal to σt3 =55.6 MPa in the defined material card) by setting correct damage factors. However, the problem " 2) It takes me 2 days to calculate (workstation, options: -nt 64), but the oscillation still happened (The velocity of the impactor is 20mm/s), so how to modify the model that I can get the smooth curve by balancing the computation time and accuracy of results? Besides, the force became zero after delamination because of separation between impactor and L-shaped specimen, however, in the experiment the force is not zero after delamination, so how to solve the problem? " is still not solved according to your suggestions. So could you help me figure it out?
13. ## Model setup of composite curved structure for delamination fracture behavior

Hello Friends, I made a ¼ symmetric 3D model for composite L-shaped structure to investigate the delamination behavior. The setup was as follows: 1) The unit: t-mm-s-MPa, Time: 1.2 s, Time frequency: 0.0012s, /AMS was used to reduce computation time. The velocity of the impactor is 20mm/s, 2) Interface Type 7 was used as contact, Igap= 0 to keep constant gap as same as Gapmin= 0.05. 3) Since I wanted to simulate delamination fracture process, I created Mat/Law 14. In the card, σt3 =55.6 MPa which is same with interlaminar tensile strength measured by the experiment, When I checked the results of stress Z and Displacement-force curve as shown in attachments, the following disagreement with experiment was found: 1) According to the time-stress curves by creating /TH/BRIC/ card , when the maximum Stress Z is 44.28MPa , the delamination fracture behavior has occurred, however, σt3 is 55.6 MPa in the model. So what should I revise? 2) It takes me 2 days to calculate (workstation, options: -nt 64), but the oscillation still happened (The velocity of the impactor is 20mm/s), so how to modify the model that I can get the smooth curve by balancing the computation time and accuracy of results? Besides, the force became zero after delamination because of separation between impactor and L-shaped specimen, however, in the experiment the force is not zero after delamination, so how to solve the problem?