Effect of temperature and humidity conditions on polymethacrylimide (PMI) foam core material and indentation response of its sandwich structures

Abstract

Foam core sandwich structures are rather vulnerable against transverse loading which can leave only barely visible damage in the structures. Environmental conditions can further affect the loading response and thus the formation of damage. To study this, uniaxial compression-tension loading tests were conducted at 30, 60 and 80 C temperatures using polymethacrylimide (PMI) foam specimens conditioned at three distinct humidity conditions (dry, ambient and wet) before testing. Effect of the conditions on the mechanical properties and loading response of the foam was studied. Strength and stiffness of the foam degraded with increasing temperature and humidity with the combined effect of these conditions being even more severe than either one alone. Indentation tests of polymethacrylimide foam core composite sandwich beams with composite face sheets were also conducted at the same temperature and humidity conditions. The indentation response was seen to correlate with the compressive response of the foam material.

Preparation of low density amorphous poly(aryletherketone) foams and the study of influence factors of the cell morphology

“…However, these composite foams have limited applications at temperatures higher than 150 C. Therefore, new types of foams must be developed to satisfy high-temperature conditions. Extensively studied high-performance foams include polymethacrylimide (PMI) foams, [1][2][3] polyimide (PI) foams, 4,5 polyetherimide (PEI) foams 6,7 and polyphenylsulfone (PPS) foams, 8,9 etc.…”

Evaluation of damage detectability in practical sandwich structure application conditions using distributed fiber optic sensor

“…The tested conditions were selected based on previous study on the indentation response of foam core sandwich structures at various temperature and humidity conditions. 20 After adhesion, the sandwich beam specimens were conditioned at various humidity conditions (dry, ambient, and wet) for 24 h before testing. For dry conditions, the specimens were kept in an oven at around 120°C where the humidity was measured to be around 10% relative humidity (RH).…”

“…Stiffness and strength of the foam core are degraded by increased humidity, which leads to increased plastic deformation in the core and formation of larger dent in the face sheet. 20 Properties of the foam are also further degraded by increasing temperature. Effect of increased temperature and humidity is thus seen as higher maximum strains and wider strained area during maximum loading.…”

“…19 Furthermore, environmental conditions and relaxation of the foam core can affect the residual dent depth. [20][21][22][23] Damage state and residual strength of foam core sandwich structures should therefore be evaluated using the damage area instead of residual dent depth only.…”

“…Foam material properties and parameters used for the Crushable foam material 20. Elastic material properties for one ply of T700S/2952 CFRP 41.…”