Due to the increased use of polymer foams in applications like lightweight protective structures and structural components, it is desirable to understand and quantify the mechanical response of these foams under different loading and environmental conditions. A typical foam exhibits crushing or cell wall bending during compression, causing a plateau region in the stress-strain curve. This allows a comparatively low increase in stress over a large strain interval, which in turn translates to good energy absorption capabilities, coupled with relatively low stresses. As FE tools are becoming an increasingly important part in the development of foam components, this requires an accurate representation of the mechanical properties. The automotive industry, for example, uses FE tools extensively in the development of pedestrian impact solutions. Furthermore, polymer foams used in outdoor applications, such as helmets and car bumpers, can be subjected to a large range of temperatures, and it is important to understand the effect this has on the mechanical response.
Expanded polypropylene foam (EPP) samples extracted from a foam car bumper have been tested in both compression and tension, at different temperatures. The foam has a nominal density of 30 kg/m^3 and testing was conducted at temperatures between -30 ºC and 60 ºC. During testing, the surface strain of the samples was determined using an in-house digital image correlation (DIC) code, allowing accurate representation of the stress-strain curve. Analysis of the test data shows a significant temperature dependence of the mechanical response. Both the Young’s modulus, collapse stress, hardening modulus and tensile failure strain depend on the temperature. For example, the collapse stress in compression at -30 ºC increases by around 100%, while the collapse stress at 60 ºC decreases by around 50%, relative to room temperature. The tensile failure strain decreases by around 65% at -30 ºC, relative to room temperature.