Session: IMECE Undergraduate Research and Design Exposition

Paper Number: 121101

121101 - Tensile Response of Lattice Structures Under Medium and Low Strain Rate Using Modified Drop Impact Tower 

The purpose of this research is to conduct dynamic tensile tests on several lattice structures in medium and low strain rates, then compare with quasi-static tensile test and to quantify the energy absorption for each loading scenario. Dynamic tensile experiments using a drop tower setup are non-conventional and require custom design. Yet, the importance of tensile testing cannot be overlooked when materials are tested for helmet design. This is because the geometry of a helmet is semispherical. The arc shape influences the loading by causing the material to experience tensile loading slightly outside of the point of impact. The material that is used exhibits viscoelastic behavior; this means that the energy absorption response heavily relates to the initial strain applied to the specimen. This is the reason that testing these structures at varying strain rates is vital to understanding the behavior of each. This can assist in the selection of which structures can potentially be used to increase protection and reduce weight of head gear by decreasing the perceived spikes in acceleration that the head would experience while maintaining the same weight or less. This data was collected using a novel drop tower setup constructed from steel in combination with an apparatus that will convert the drop tower’s compression force into a tensile force directed into the specimen of choice. A TE 830M1 2000g accelerometer sampling at 1MHz was attached to the bottom side of the dynamic frame in order to track the acceleration that the specimen will experience; this data was collected using LabView. In addition to this, a 16000 fps Photron camera recorded the event in order to better track and visualize structure deformation using DIC software. The application of medium strain rate in addition to low strain rate is to cover the entire range of conditions that a helmet can reasonably be expected to experience. The same lattice structures were tested in a tensile testing machine to understand the mechanical properties in a low strain rate loading condition. The data from both loading conditions will be placed against theoretical acceleration and deformation that will be calculated by hand in order to verify methodology; this is to better predict the behavior of any structure that may be used in the future. I predict that the behavior of the structures in tension will show significant differences between quasi-static testing and dynamic testing due to the viscoelastic nature of the structures in question. The understanding of this data will enable future design of head protection. 

Presenting Author: John Cross University of Texas at Arlington

Presenting Author Biography: My name is Ethan Cross and I am a 4th year Mechanical Engineering student at the University of Texas at Arlington. My professional goals are to finish my bachelors degree and continue to pursue a PhD in Mechanical Engineering. With the knowledge and experience gained from my PhD, I would like to continue work in research focused either in clean energy solutions or unmanned vehicle design. In my personal life, I am a disciplined rock climber and avid backpacker; I find that there is no escape quite like being hundreds of feet up a cliffside. My goal in life is to never stop learning and hope that the knowledge I gain can be used in some way to better the lives of others.

Authors:

John Cross University of Texas at Arlington
Ashfaq Adnan University of Texas at Arlington