A Study on Reliability-Based Maximum Service Temperature Estimation of Plastic Automotive Parts

Recently, the environmental temperature of vehicles is changing due to the electrification of vehicles and improved internal combustion engine system to reduce carbon emissions. However, mechanical properties of plastic materials change very sensitively to environmental temperature changes, and mechanical properties decrease when exposed to high temperatures. Therefore, it is important to estimate lifespan estimation of plastic parts according to temperature changes. In this paper, reliability analysis process to estimate the maximum service temperature of plastic parts was developed using aging data of material properties, environmental condition data of automotive parts, and field driving condition data. Changes in the mechanical properties of plastic materials such as glass fiber reinforced polyamide materials were tested. The environmental exposure temperature of the vehicle and parts was measured, and the general driving pattern of the vehicle was analyzed. Weibull aging model and Arrhenius physics model was applied for lifespan estimation of materials. The damage rate theory was applied to obtain the sum of damage rates in various temperature conditions since automobiles are exposed to various temperature conditions. The damage rate according to the temperature and time exposed to the environment was calculated with lifespan estimation results of materials and environment conditions of plastic parts, then the maximum service temperature that can satisfy the warranty period of the product was predicted. As case studies, the maximum service temperature of the air intake manifold, the bracket part that support the motor in EVs or the transmission in internal combustion engines with glass fiber reinforced polyamide was predicted with reliability-based maximum service temperature estimation method.