We all know that simulation is capable of providing insights into a large number of design iterations quickly and efficiently. This analysis exemplifies exactly that – and how the results allow selection of optimum designs prior to any physical testing. Of course, we can’t include the real results of the analyses – NDAs are important – but a simplified version shows what the results looked like.
Problem Statement
The customer (a prominent manufacturer of very high-end sport and travel cases) came to Fidelis as they were in the process of designing a new mid-size travel suitcase that needed to be both robust to typical handling abuse as well as lightweight and sleek. They were able to provide the CAD for the product as well as some materials that they were interested in studying (various polymer grades) and wall thicknesses. The concern, from their point of view, was permanent deformation of the structure at drop heights of over 6ft, which can be typical during baggage handling at an airport for example. Five different drop orientations were provided.
Methodology
Since this was a drop test, the Abaqus explicit/dynamic solver was utilized. This means that inertial effects could be considered and subsequent damage assessed after a fall of 6ft. An initial velocity was applied to the assembly, which subsequently struck a rigid plane (representing the ground). It was also important to include a rated payload in the case, and this was represented by a very low stiffness block, relevant to clothes or other fabric items. Now, the customer was primarily interested in the performance of the shell of the suitcase, and less so about the ancillary components, so a highly detailed shell mesh was generated for that region. The rest of the components were represented with reasonably coarse mesh and linear material properties.
Another key aspect of these analyses were the material properties. Initially, we were provided with low/static strain-rate data, typical of most polymer data sheets. However, given the short timeframe of the impact, it immediately became apparent that strain-rate dependent material properties would be necessary. Since these were not available from either the customer or the material supplier, Fidelis was able to estimate the effects based upon a detailed search of available literature.
Results and Conclusions – Our Value
Once all of the different load cases, material and wall thickness combinations had been analyzed, we were able to present the customer with both stress and strain data at the point of impact (suggesting whether failure/cracking of the material was likely) as well as a visual image of the dent size at each impact location. This allowed specific material/design/thickness combinations to be eliminated and a final best-case version to be identified. All of which reduced customer prototyping expenses by 10s of thousands of dollars.
TL;DR
Fidelis was able to significantly reduce the design cycle and prototyping cost of a high-end suitcase by using explicit/dynamic analysis to simulate drop testing. Acceptable permanent deformation was assessed by the customer based upon both aesthetics and function and a final design decision was made, all without any costly physical prototyping.
