LS-DYNA Case Studies
Drop Test Analysis of Transportation Container
Objective: Numerically demonstrate using reliable and conservative procedures that the Harris Thermal US DOT Type A Transportation Container (DWG #23762) can maintain containment integrity during a drop-test from a height of 1.14 m (45 in.) onto a rigid surface per DOT Specifications 49-CFR-173.465(a).
Modeling Assumptions and Details: A detailed and comprehensive finite element analysis (FEA) model was constructed using an approved drawing set (DWG ref. #23762) from Harris Thermal Transfer Products (HTTP). This model was developed in close collaboration with HTTP and contains all relevant design features of the designed Duratek Type-A Container (known henceforth as "Duratek Container").
The FEA model was constructed using best industry practices. For example, care was exercised to ensure a high density of mesh granularity in regions of expected high stress. The model was constructed to contain a majority of 4-node plate elements with solid regions meshed with 8-node bricks. Beam elements were used to model the bolted connections between the lid and the top of the Duratek Container. The model consists of approximately 30k nodes and 29k elements.
The analysis engine used to generate all numerical results is LS-DYNA v970. This explicit FEA solver is an industry standard for crash and drop-test simulations.
Units used in this analysis are lbf, inch, and seconds. Stresses are reported in psi and deflections in inches.
The container has an approximate weight of 14,400 lbf. The weight of the container contents is 10,000 lbf. The total impact weight is 24,400 lbf. The container contents are assumed to be uniformly distributed within the container. At this weight the container falls somewhat on the border between the two weight classes provided in the DOT specification (see Appendix). To maintain conservativeness in this analysis, the higher drop height of 36" was chosen.
The load set assumes that the container is dropped from a height of 1.14 m (45 in). Numerically this is accomplished by positioning the container immediately above a rigid surface and applying a uniform initial velocity of 186 in/sec and a uniform acceleration of 386 in/sec^2 to simulate gravity. The container is assumed to drop at a 45-deg angle from two orthogonal vertical planes (graphical descriptions are provided in the body of the report) onto its most vulnerable corner. The drop angle and the chosen corner are believed to provide the most severe drop-test conditions. Importantly, the drop height provides an additional 25% more impact energy than that specified in the DOT regulation (36"). Consequently, the calculated damage within the FEA model can be considered to be highly conservative.
The container impacts a perfectly rigid surface that is undeformable. This modeling idealization fully complies with the DOT specification 49-CFR-173.465(a) Section 5.
The lid is pre-tensioned per standard operating procedure for the utilization of the Duratek Container.
Contact behavior was enforced between all contacting surfaces. This numerically complicated behavior is efficiently implemented within the LS-DYNA solver and induces only a modest computational penalty during solution.
Analysis Results: Drop-test results indicate significant and noticeable plastic damage at the corner of the structure. Due to the design of the Duratek Container, this damage was restricted to the very extreme surfaces of the container and did not affect the integrity of the main walls of the container. The large steel block used to frame the outer corner of the container suffers the brunt of the impact damage and transfers this load cleanly into the inner floor and side walls of the Duratek Container. Advantageously, this design feature allows the impact load to be evenly distributed into the container structure during the impact event.
Conclusion: Conservative numerical simulations indicate that the integrity of the Duratek Container will be maintained during and subsequent to the impact event. Based on this simulation, the Duratek Container completely meets the DOT Specifications 49-CFR-173.465(a).