1. ANSYS/LS-DYNA Drop Test Module
Chapter 12
ANSYS/LS-DYNA Drop Test Module

2. Chapter Objectives
Upon completion of this chapter, students will be able to perform a basic drop test analysis using the ANSYS/LS-DYNA Drop Test Module (DTM)
1. Define and describe a drop test analysis
2. List typical applications for performing a drop test analysis
3. Introduce the ANSYS/LS-DYNA Drop Test Module (DTM)
4. Describe in detail the steps required in performing a drop test analysis using the DTM
5. Given step-by-step guidance, a basic drop test analysis will be performed
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3. Drop Test Analysis - Definition
A drop test analysis simulates an object’s behavior in an actual drop test. An actual drop test would typically involve releasing an object in a gravitational field from some height, and allowing it to drop and impact a flat, rigid surface.
Reasons for Performing a Drop Test Analysis
Many objects, or “parts”, are at times dropped onto a floor or the ground, either by accident or through standard usage. A reliable part must be designed to withstand the impact. A design can be evaluated by performing a drop test of a prototype part. A virtual drop test analysis, which is a computer simulation of the actual drop test, may also be performed.
A virtual drop test analysis can be performed at the design stage, while an actual drop test requires that a prototype part be built. From the virtual drop test analysis, stress levels and high stress locations in the part can be identified, so that design modifications can be implemented if needed. A modified design can be evaluated by simply modifying the finite element model of the part, and performing a new analysis, without building a new prototype.
It is advisable to correlate analysis results with actual drop test results. Once a correlated model is obtained on one prototype design, proposed design modifications may be evaluated with greater confidence through analysis, without building a modified prototype.
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4. Typical Applications for Drop Test Analysis
Tools - Hammers, pliers, screwdrivers, etc.
Electronics - Laptop computers, televisions, CD players, etc.
Appliances - Refrigerators, washers, dryers, microwaves, etc.
Industrial - Toxic chemical storage drums.
Packaging for consumer goods.
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5. Eight Basic Steps for Performing a Drop Test Analysis with the DTM
There are eight basic steps required to perform a basic drop test analysis. These steps include:
1. Import or create the model.
2. Enter the Drop Test Module.
3. Orient the object.
4. Define the magnitude of the acceleration due to gravity, g.
5. Define the drop height.
7. Solve the analysis
8. Animate the results.
The following pages are devoted to describing each of these steps in detail.
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6. Step 1: Import or Create the Model
The user must prepare or import the model of the object to be drop tested. The model can be imported from a CAD package or created using the procedures outlined previously in this course.
The object must be fully defined prior to entering the “Drop Test” portion of the ANSYS Main Menu! All of the elements and material properties, including damping, need to be already specified.
Only elements which are compatible with LS-DYNA (ELEM ) should be included in the model. These elements are discussed in the ANSYS/LS-DYNA User’s Guide.
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7. Step 2: Enter the DTM and Initialize the Model
The DTM is entered by choosing Drop Test from the ANSYS Main Menu
Once the DTM is entered, the Drop Test Main Menu (DTMM) Appears.
It is advisable to save a copy of the model prior to initializing the drop test module. This is done done selecting: Initialize > OK
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8. Step 3: Orient the Object
The model can be oriented with respect to the gravitational field by selecting Orient Model from the DTMM. The user specifies the “up” direction (opposite to g) using one of the options: Drop Test Orient Model
The following is a description of the five orientation options:
1) Dynamic Mode: The model is rotated on-screen. The up direction in the screen view orientation is assumed to be opposite to the direction of g.
2) Input Vector: An upward-pointing vector is specified in global Cartesian coordinates.
3) Pick 2 Nodes: Up is assumed to be from the first picked node to the second.
4) Pick 1 Node and CG: Up is from the object center of gravity (CG) to the picked node.
5) Rotate about WY: This option is primarily useful in changing the default Drop Test viewing orientation. The WY-direction is the specified “up” direction.
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9. Step 4: Define the Magnitude of g
The direction of g is specified when the object is oriented. The magnitude is specified by selecting Define g from the DTMM, which brings up the dialogue box below. The magnitude chosen must be consistent with the units used in creating the model.
Drop Test: Define g ...
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10. Step 5: Define the Drop Height
The drop height is specified by selecting Drop Height from the DTMM. The height specified must be in units consistent with those used when creating the model. The height is measured along the WY-axis (directed “up”) from the center of the top face of the target to a user-selected reference point. This point can be:
1. The lowest point on the object being dropped.
2. The object center of gravity.
3. A selected node on the object.
4. A specified point on the object.
Drop Test: Drop Height
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11. Step 6: Specify Solution Controls
Solution controls are specified by selecting Solution Ctrls from the DTMM. The total solution time, result file and time-history output intervals, and the analysis starting time option are input. When the Near Impact Time starting time option is used, the analysis begins just prior to impact, saving computation time.
Drop Test: Solution Ctrls....
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12. Step 6: Specify Solution Controls
In the solution controls dialogue box, the user also has the capability of specifying nodes for subsequent time-history postprocessing. In addition, the node nearest the center of gravity of the object can be calculated and automatically saved for postprocessing.
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13. Step 7: Solve the Drop Test Analysis
Once the user has input all the required drop test parameters, the solution phase is entered by selecting Solve from the DTMM. Upon selecting “Solve”, a note is printed to the screen with a brief summary of the input data, along with the dialogue box below. When OK is selected, the solution begins.
There are some advanced options that have not been included in this basic drop test description. These are covered in the full ANSYS drop test manual. Additional features include:
1. Modifying the target properties.
2. Defining advanced contact parameters.
3. Obtaining additional information on the model before performing the drop test.
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14. Step 8: Animate the Results
The dynamic results, such as von Mises stresses in the dropped object, can be animated over the solution time by selecting Animate Results from the DTMM. The dialogue box for the ANDYNA animation macro appears, which is similar to ANDATA animation macro (Over Results) available from the Utility Menu.
Drop Test : Animate Results …
Alternatively, the animation macros in the Utility Menu can be used. Also, the standard POST1 plotting routines are available.
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15. Drop Test Module Exercise
The exercise for this chapter begins on page E12-1 of Volume II.
The ANSYS/LS-DYNA Drop Test Module is used to easily set up the simulation of a screwdriver being dropped onto a rigid surface.
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