Experimental and Numerical Research of Delamination Process in CFRP Laminates with Bending-Twisting Elastic Couplings

Abstract

This paper aims at experimental and numerical research of delamination process in carbon/epoxy composite laminates with different fiber orientation angles in stacking sequence exhibiting the bending–twisting elastic couplings. Experimental specimens were subjected to the double cantilever beam (DCB) tests according to the ASTM D5528 regulations. Values of the mode I strain energy release rates were calculated by using three different data reduction schemes: the modified beam theory, the compliance calibration method and the modified compliance calibration. Determination of delamination initiation point was conducted in twofold way: by visual observation of crack tip using high resolution camera and by utilization of the acoustic emission technique. Numerical analyss were prepared in Abaqus/CAE Software environment by using the virtual crack closure technique (VCCT). The numerical beam model consisted of SC8R continuum shell elements. Obtained outcomes revealed that extensive fiber bridging phenomenon occurring during delamination process pronouncedly affected propagation values of strain energy release rate (GIprop) and numerically obtained load–displacement curves. Nevertheless, in initial stage of delamination, results obtained by using the VCCT were in agreement with experimental data. The greatest value of the mode I fracture toughness equal 0.56 N/mm was obtained for the BT45 laminate.

Numerical Study of the Natural Oscillations of Perforated Vibrating Surfaces with Holes of Complex Geometry

“…The study of the perforated vibrating surface oscillations, in this formulation of the problem, refers to the oscillations of a flat rectangular plate with holes. The research plan consists of: The use of numerical methods for the analysis of oscillations of various complex structures of composite laminates [22], damaged cantilever beams [28], including perforated plates [24,25] showed the necessary accuracy of the results. Preliminary studies with experimental and numerical methods produced an adequate numerical FE-model at Abaqus [29].…”

“…We also take the following conditions: rectangular configuration, homogeneity by material properties. The well-known methodologies for measuring the natural oscillation frequency consist of analytical methods, for example, Rayleigh's method [20] or based on the Rayleigh quotient and the Rayleigh-Ritz method [21]; experimental methods such as, using high resolution camera and by utilization of the acoustic emission technique [22], use of accelerometer under different conditions of plate fixation [23]; numerical methods, for example, using finite element package ANSYS with varying sizes and shapes of single holes [24], for square or rectangular shape of plates [25]. Most of the methods are based on the study of the natural oscillation frequency of research objects -plates with a single hole of regular geometric shape [25], isotropic and orthotropic properties [20], various boundary conditions in the form of relative coordinates of the location of the holes [26] or changes in the size of the central hole and the points of fixing the plate [27].…”

Numerical Analysis of Lamb Wave Propagation in Composite Plate with Different Fiber Orientation Angles – Acoustic Emission Approach

“…Thanks to high sensitivity, this method can easily detect different microscale defects occurin the form of cracks or structural flaw. Referring to the fiber reinforced composites, the AE technique [2][3][4][5][6] is a promising tool in detection of delamination phenomenon [7][8][9] that is the most common type of failure in that type of materials. The basic principle of the AE method is detection of elastic waves generated by strain energy accumulated inside material and released during development of fracture mechanism.…”

Identification of the Natural Frequencies of Oscillations of Perforated Vibrosurfaces with Holes of Complex Geometry

“…A synthesis of different methods makes it possible to obtain the most accurate results in the study of plate oscillations. Thus, studies of a rectangular plate, which is made of various materials and has variable boundary conditions, carried out by experimental and numerical methods, made it possible to obtain adequate results [25][26][27].…”