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

Abstract

Various modifications of the face/core interface in foam core sandwich specimens are examined in a series of two papers. This paper constitutes part I and describes the finite element analysis of a sandwich test specimen, i.e. a DCB specimen loaded by uneven bending moments (DCB-UBM). Using this test almost any modemixity between pure mode I and mode II can be obtained. A cohesive zone model of the mixed mode fracture process involving large-scale bridging is developed. Results from the analysis are used in Part II, which describes methods and results of a series of experiments.

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

“…For the specimen utilized in this study, 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. This is described in Part I [1].…”

“…As described in Part I [1] a face/core interface crack in a sandwich structure may propagate in three basic ways: (1) self similar in the interface, (2) kink into the core or (3) kink into the face. The actual path depends on the fracture resistances of the face, core and interface and the mode-mixity of the applied loading.…”

“…Table 2 Test matrix for a total of 83 specimens; number of replicates, core type, interface lay-up, moment ratios, and corresponding average mode-mixity m avg and crack tip mode-mixity m tip are found from simulation of the DCB-UBM specimen, see [1] The following superscripts are used: "r" marks the reference specimens, "w" indicates that the test is repeated for 20 and 40 mm specimens to explore the influence of specimen width and "s" entails that the face laminate is stitched …”

“…The sandwich specimens were loaded by pure bending moments applied at the end of the specimen. Details regarding the test-rig and loading principle are thoroughly described in [7] and a procedure for evaluating the J integral is presented in Part I [1]. Prior to conducting the test a speckled pattern is applied to the specimen surface by using first white and then black spray paint.…”

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.…”