| Objectives | Background | Approach |
A test methodology will be developed to simulate the
fundamental aspects of impact loading encountered when a
portable product is dropped. The accompanying PoF analysis
needed to tailor the test and interpret the results will be
defined. The principles will be demonstrated through a
specific case study.
Impact loading caused when a product is dropped, causes two types of loading. One is inertial loading leading to significant deformation magnitude and rate in all flexible portions of the structure. The other is a propagating stress wave emanating from the contact site. While both contribute to impact damage in portable electronics, the former contributes more in a compliant structure, while the latter dominates in a stiff structure. In this study, the emphasis is primarily on the former, as failures due to inertial loads are expected to dominate in most portable electronic devices.
Assessment of impact resistance is extremely challenging because transient impact response is very structure-specific. It is therefore not possible to create a generic test specification for impact, but it is certainly possible to use PoF principles to describe a generic methodology for developing impact tests that are tailored to each product family.
An instrumented hammer-impact facility will be developed to perform controlled shock tests. For convenience of demonstration, a simple PWA specimen with dummy components, connectors and displays will be selected. Member companies will be requested to provide this specimen. The purpose of choosing this simplified specimen is to restrict the study to only a few known potential failure mechanisms. The selected product will be designed to retain the form and fit of a typical portable electronic device.
The specimen will be subjected to a measured shock, perpendicular to the PWA plane. The energy of the impact will be measured with instrumentation. The test will be repeated at progressively increasing impact levels until failure occurs. The impact energy will be changed by changing the hammer weight and/or velocity. The entire test sequence will then be repeated along other orthogonal in-plane axes. Failure analysis will be conducted to ascertain the failure mechanism. The entire test matrix will be replicated thrice for proof of consistency of this data.
PoF simulations of the product will be conducted to determine the strain magnitude and strain rate at the failure site. The failure data will be presented to the membership in the form of the ability of the relevant failure modes to withstand different drop repetitions, of a given strain magnitude and given strain rate. Guidelines will be developed to conduct this test for any given product family.