Temperature Chamber for Adhesive Bonding Properties From Mode Specific Testing Specimens

Abstract

Adhesive use in fastening is increasing in many industries. Modeling the behavior of adhesives allows joints to be optimized, decreasing costs from over-design and validation testing. Unfortunately, available adhesive material properties provided by manufactures are often insufficient to accurately model and predict behavior under real-world conditions. An adhesive joint in service is often subjected to a combination of mode I (tensile) and mode II (shear) loading. Also, when used in outdoor environments, ambient temperatures can vary from below freezing to over 40°C. This paper describes a project to measure the relevant adhesive material properties at the environmental conditions of interest for two specific adhesives and to use them in subsequent modeling. The needed material properties have been found to be mode I cohesive strength, mode I cohesive toughness, mode II cohesive strength, and mode II cohesive toughness. These properties are measured individually using four tests that isolate each of the material properties by using specimens with distinct geometries and loading conditions. These geometries allow the process zone of the adhesives to be controlled. A large process zone will relate to the cohesive strength, and a small process zone will relate to the cohesive toughness, in either mode I or mode II loading. Since the values of cohesive strength and toughness of the adhesives included in this study are unknown before testing, iterations of each specimen are varied by changing the process zone size to ensure valid properties are measured. Testing is conducted at −30°C, 20°C, and 45°C. In order to conduct this testing a temperature chamber was designed, fabricated, and validated. Commercially available temperature chambers were either too small or prohibitively expensive. The temperature chamber this project created was constructed of laser cut and bent stainless steel sheets with an insulated double-wall construction. Two seals were used at every entry point to maintain an air-tight chamber. A heating and cooling circulator and heat exchanger were used for temperature control. The chamber can heat to 45°C in approximately 15 minutes, and cool to −30°C in approximately 30 minutes.