Non Destructive Testings on Damaged Multi-Cores Materials Sandwich Structures

Sandwich structures are widely used in aeronautics both for primary and secondary structures such as landing gear doors, flaps or floors. Multi-cores materials sandwich structures presents many advantages. By adding layers with another materials that the core one, extra properties can be obtained as heat or impact protection. Manufacturing quality must be controlled and therefore bonding needs to be inspected. In this paper bonding defects between multi-layers of sandwich specimen are inspected through Non Destructive Tests. Due to its large use in industry, ultrasonic phase array is used to detect manufacturing bonding defects. Three different type of multi-cores materials specimen are investigated. Results show that due to the high PVC foam porosity, defects cannot be detected both between composite skins and foam and between foam and core material.

Influence of Dynamic Loading on Fracture Behaviour of DCB Sandwich Specimen

Numerical simulations of dynamic fracture behaviour of a double cantilever sandwich beam subjected to uneven bending moments in plane conditions are carried out using the dynamic finite element analyses with the ABAQUSTM code. The strain energy release rate was evaluated by means of the finite element model developed within the two-dimensional (2-D) linear elastodynamic theory. This demonstrates the capability and the reliability of the finite element modelling as an extremely useful numerical tool for solving dynamic fracture mechanics problems. Also, the dynamic behaviour of fracture parameters and interface crack progression is discussed.

Mode mixity analysis of face/core debonds in a single cantilever beam sandwich specimen

The single cantilever beam sandwich specimen has been proposed, as a fracture test standard for mode I peel loading. Critical parameters, including specimen dimensions, determine whether the crack propagates along the face/core interface in mode I during the fracture test. This paper outlines a parametric study based on a numerical method to examine local mode mixity conditions for a wide array of sandwich systems by varying several geometrical and material parameters. The thickness and modulus of the face sheet were seen to influence the mode mixity for most sandwich systems. Core Poisson’s ratio was shown to influence the local mode mixity and has the capability of driving the crack along the interface or into the core. The effect of the intact specimen length was analyzed and presented from a mode mixity perspective based on various elastic foundation modulus expressions. Reinforcement of the single cantilever beam specimen with stiff layers was also investigated numerically and compared with a similar analysis in the literature. The analysis presented in this paper shows that, despite reducing the global shear component, the local mode mixity condition deviated away from the mode I regime for several sandwich specimens. An appropriate foundation model along with a minimum loading rod length was one of the recommendations provided from the analyses, which may supplement the ASTM International standardization efforts.