Tailoring Sandwich Face/Core Interfaces for Improved Damage Tolerance—Part II: Experiments

Abstract

A face/core debond in a sandwich structure may propagate in the interface or kink into either the face or core. It is found that certain modifications of the face/core interface region influence the kinking behavior, which is studied experimentally in the present paper. A sandwich double cantilever beam specimen loaded by uneven bending moments (DCB-UBM) allows for accurate measurements of the J integral as the crack propagates under large scale fibre bridging. By altering the mode-mixity of the loading, the crack path changes and deflects from the interface into the adjacent face or core. The transition points where the crack kinks are identified and the influence of four various interface design modifications on the propagation path and fracture resistance are investigated.

Tailoring Sandwich Face/Core Interfaces for Improved Damage Tolerance—Part I: Finite Element Analysis

“…8 m is used to associate any applied moment ratio with a certain m tip and m avg in the experimental part of this paper series, [4]. materials tested in part II, crack deflection into the core does occur for some M 1 /M 2 ratios, even though the shear direction is positive.…”

“…A schematic illustration of the test rig and the loaded sandwich specimen is shown in [4] and a more detailed description is given in [5]. For the DCB-UBM specimen the J integral can be determined analytically from specimen geometry, elastic properties and applied moments by considering a contour along the outer boundaries of the specimen, see Fig.…”

“…2a. Pre-crack (4) The face laminate is stitched with an aramid thread before resin impregnation to sustain the face layers together hereby limiting the tendency for crack kinking into the load-carrying laminate. The specimen with stitching is schematically illustrated in Fig.…”

“…This first paper presents the finite element analysis while part II [4] describes the experimental analysis. The test specimen is a sandwich version of the double cantilever beam loaded by uneven bending moments (DCB-UBM) [5], whereas the sandwich version was presented in [6].…”

Interfacial crack arrest in sandwich beams subjected to fatigue loading using a novel crack arresting device – Numerical modelling

“…In a recent study of a proposed crack arresting device, a CZM method was utilized to calculate the crack propagation and mitigation due to fibre bridging for an increasing crack length [15][16][17]. Other crack arrester concepts were proposed in [18][19][20], where FE analysis was used to demonstrate the efficiency of the crack arresting elements.…”