Combined Temperature and Moisture Effect on the Monotonic and Fatigue Strengths of Sandwich Beams with Glass-Polypropylene Faces and Aluminum Foam Cores

Abstract

Recently, the sandwich structures with thermoplastic faces and metal foam cores have been received much attention in the automobile, aerospace and naval industries. Since the material properties of the polymer-based faces and adhesive films employed in the sandwich structures are sensitive to the temperature and humidity, the knowledge of the environmental effect on the mechanical properties are important to the design and application of such structures. Therefore, the hygrothermal effect on the static and fatigue bending strengths of the sandwich beams with glass-polypropylene faces and aluminum foam cores were experimentally analyzed in the present study. The monotonic and cyclic four-point bending tests were conducted under four environmental conditions, i.e., 25°C/45% RH, 25°C/75% RH, 50°C/45% RH, and 50°C/75% RH, to evaluate the influence of combined temperature and humidity on the strengths against the static and cyclic flexural loads. Experimental results show that the humidity has tiny effect on the static and fatigue strengths when the specimens were tested at fixed temperature. However, the temperature plays an important role in the environmental effect because the monotonic and fatigue strengths of the studied sandwich specimens decrease significantly when the ambient temperature rises from 25 to 50°C. Furthermore, under four considered environmental conditions, two crack systems, the core shear ones and the face/core interfacial ones, were observed both in the monotonic and cyclic tests. The development of interfacial cracks strongly depends on the environmental variables. Accordingly the interfacial cracks play an important role in the static and fatigue strengths of the studied sandwich structures.

Fatigue of an Aluminum Foam Sandwich Formed by Powder Metallurgy

“…Harte et al [ 23 ] investigated the fatigue performance of an AFS with four-point bending, determined the different failure modes caused by the size effect, obtained the failure mode diagram of the AFS, and verified the effectiveness of the diagram through experiments. Jen et al [ 24 ] investigated the effects of temperature and moisture on the static and fatigue properties of aluminum foam sandwich structures, and the experimental results showed that moisture had little effect on static strength and fatigue strength, and temperature played a more important role. Yan et al [ 25 ] explored the fatigue damage mechanism of carbon fiber panel structures and proposed three microscopic damage mechanisms: stress concentration at the cell ridge or cell wall, damage at the thinnest position of cell wall, and damage caused at the intersection of cell wall.…”