Static Mechanical Properties of Expanded Polypropylene Crushable Foam

Abstract

Closed-cell expanded polypropylene (EPP) foam is commonly used in car bumpers for the purpose of absorbing energy impacts. Characterization of the foam’s mechanical properties at varying strain rates is essential for selecting the proper material used as a protective structure in dynamic loading application. The aim of the study was to investigate the influence of loading strain rate, material density, and microstructure on compressive strength and energy absorption capacity for closed-cell polymeric foams. We performed quasi-static compressive strength tests with strain rates in the range of 0.2 to 25 mm/s, using a hydraulically controlled material testing system (MTS) for different foam densities in the range 20 g/dm3 to 220 g/dm3. The above tests were carried out as numerical simulation using ABAQUS software. The verification of the properties was carried out on the basis of experimental tests and simulations performed using the finite element method. The method of modelling the structure of the tested sample has an impact on the stress values. Experimental tests were performed for various loads and at various initial temperatures of the tested sample. We found that increasing both the strain rate of loading and foam density raised the compressive strength and energy absorption capacity. Increasing the ambient and tested sample temperature caused a decrease in compressive strength and energy absorption capacity. For the same foam density, differences in foam microstructures were causing differences in strength and energy absorption capacity when testing at the same loading strain rate. To sum up, tuning the microstructure of foams could be used to acquire desired global materials properties. Precise material description extends the possibility of using EPP foams in various applications.

Biophysical Properties of Foamed and Solid Polymers Used in Orthotics and Prosthetics

“…The overview of mechanical properties shows huge differences between solid polymers and foamed polymeric materials. The Young's modulus and the maximum tensile stress for solid PE and PP are much larger compared to the foamed materials, which is in line with the results in literature [1,12]. Young's modulus and the maximum tensile stress of selected samples of solid polymers are 1380-2250 MPa and 28.3-33 MPa, respectively, while for foamed polymeric samples values vary between 1.54 MPa and 43.8 MPa (Young's modulus) and between 0.898 MPa and 2.03 MPa (maximum tensile stress).…”

“…The foam toughness can be also increased by increasing its density and molecular weight. It was reported that by tailoring the microstructure of foams desired comprehensive materials properties could be achieved [12].…”

Expanded Beads of High Melt Strength Polypropylene Moldable at Low Steam Pressure by Foam Extrusion

“…T foam is a very important process variable for defining the final foam structure both in terms of density and morphology. A bell-shaped curve typically describes the effect of T foam on the foam density, with a maximum of the expansion ratio at optimal temperature, Below , the viscosity of the polymer increases, and crystallization or vitrification may occur [ 28 , 29 , 30 ]. Above , the reduction of the polymer viscosity induces bubble coalescence, and the increased diffusivity of the blowing agent is responsible for its loss through the external surface of the strand, followed by a corresponding reduction of foaming efficiency.…”

Prompt Determination of the Mechanical Properties of Industrial Polypropylene Sandwich Pipes

“…These results can be considered suitable, as these differences were caused by many variables [ 47 , 48 , 49 ], as well as the results of interpolation of m -layer foam.…”