Drop test analysis of a Cellphone model using LS-Dyna

Objective: Creation of input deck for simulating cellphone drop test.

Procedure:

• Open the supplied .k file, which contains the mesh information of the mobile and the ground.

Fig 1: Mesh information of the cellphone and the ground.

• The gound mesh contains both shell and solid elements. Red color elements are the shell elements that should be deleted from the model.
• Navigate to the Element tools>Element Editing options from the right hand menu ribbon.

Fig 2: Element editing options.

• Select the shell elements from the ground and delete them so that only solid elements remain within the mesh.

Fig 3: Model containing only solid elements.

• The initial keyword file contains only the element, node, and parts information available within it. To fully develop the deck file to simulate the drop test, necessary keyword cards must be added to the model.

Fig 4: Initial keyword file information.

• To start with the deck preparation, we rename the auto-created parts with a suitable name and part ID to distinguish them and for further use.

Fig 5: Rename the parts and IDs to differentiate them.

• Navigate to Model>Create entity options from the right hand menu ribbon. In the *SET_NODE option from the set data drop-down, we create two separate node sets representing cell phone and rigid wall, respectively.

Fig 6: Two node sets are created.

• For constraining the rigid walls motions, from the same create entity options expand the boundary menu. Single Point Constraint (SPC) is listed. Using this command constraint, the node-set for the rigid wall created earlier in all directions.

Fig 7: Create SPC to restrict the motions of the gound.

• To provide initial velocity to the cell phone, the velocity keyword from the initial deck is chosen. Entering the node-set id and the velocity value in the z-direction defines it ultimately.

Fig 8: Velocity is defined for the cell phone.

• Two materials cards are defined for the cell phone and the rigid wall.
• MAT024-PIECEWISE_LINEAR_PLASTICITY is defined with the following properties for the cell phone.

Density: 0.0078500 gm / mm³

Elastic Modulus: 210000 Mpa

Poisson’s Ratio: 0.3

Tensile Yield Strength: 314 MPa

• MAT020-RIGID is defined with the following properties for the ground.

Density: 0.0078500 gm / mm³

Elastic Modulus: 210000 MPa

Poisson’s Ratio: 0.3

Fig 9: Material properties are assigned with appropriate material laws for the mobile and the ground.

• A solid section keyword is included with solid element formulation(ELFORM=1).

Fig 10: Element formulation is defined for the solid elements.

• The material and the element formulation should be assigned to the parts we have created earlier.

Fig 11: Material and section are assigned to the parts.

• Since the mobile and the ground come in contact during the simulation, contact must be defined.
• AUTOMATIC_SURFACE_TO_SURFACE contact card is defined with the following data entries.

Fig 12: Contact is established between the ground and the cellphone.

• The ASCII_option keyword from the DATABASE deck is used for the output requests, and GLSTAT and MATSUM options are checked.

Fig 13: Output requests are defined.

• The BINARY_D3PLOT keyword from the DATABASE deck is used for the plots, and a DT of 0.01 is entered.

Fig 14: Plots at time intervals are defined.

• The TERMINATION keyword from the CONTROL deck is used to define the end time of the simulation.

Fig 15: End time for the simulation is defined.

• With all these keywords included, the deck is fully defined and is now ready to solve.

Fig 16: Fully defined deck for the drop test.

• Open the Start LS-Dyna analysis, browse the keyword file, and hit run to run this keyword file.

Fig 17: LS-Dyna analysis browser.

Fig 18: Successful completion of solving.

• Open new LS-PRE POST from the launch manager and open the LS-DYNA Binary plot (choose the D3PLOT file created) from the file menu.
• The model will be loaded the same as before, but we can access only the post-processing options from the right ribbon menu.

• The above animation represents the mobile drop on the ground.
• Within the Fringe Component, multiple quantities are listed to visualize the contours.

Fig 19: Fringe component menu.

• The above animation shows the von-mises stresses produced in the mobile due to the drop.

Fig 20: Stress contour at a time of 0.05ms.

• Navigate to the ASCII option from the right ribbon to plot the different variables, and a separate menu pops showing the output requests.

Fig 21: ASCII options for plotting the graphs.

• Each output request has different data quantities available within them to plot. Whatever file is required, it is loaded first, and the required quantities are chosen for plotting.

• The above graph represents the kinetic, internal, total, and sliding energy available in the GLSTAT.

• The above graph represents the displacement of the phone available in the MATSUM.

Conclusion:

The complete keyword file is generated from the given primary file. A solver deck has been created to perform the cell phone drop test with post-processing data.