A review provided about non-destructive testing (NDT) methods for the evaluation of composites. The review considers the capabilities of most common methods in composite NDT applications such as Visual Testing (VT or VI), Ultrasonic Testing (UT), Thermography, Radiographic Testing (RT), Electromagnetic Testing (ET), Acoustic Emission (AE), and Shearography Testing with respect to advantages and disadvantages of these methods. Then, methods categorized based on their intrinsic characteristics and their applications.

https://cyberleninka.org/article/n/593997.pdf

A review of non-destructive testing methods of composite materials

Advances, limitations and prospects of nondestructive testing and evaluation of thick composites and sandwich structures: A state-of-the-art review

Measurement of true stress–strain curves and evolution of plastic zone of low carbon steel under uniaxial tension using digital image correlation

For high performance 3D orthogonal textile Carbon/Carbon (C/C) composites, a key issue is the manufacturing defects, such as micro-cracks and voids. Defects can be substantial perturbations of the ideal architecture of the materials which trigger the failure mechanisms and compromise strength. This study presents comprehensive investigations, including experimental mechanical tests, micron-resolution computed tomography (μCT) detection and finite element modeling of the defects in the C/C composite. Virtual C/C specimens with void defects were constructed based on μCT data and a new progressive damage model for the composite was proposed. According to the numerical approach, effects of voids on mechanical performance of the C/C composite were investigated. Failure predictions of the C/C virtual specimens under different void fraction and location were presented. Numerical simulation results showed that voids in fiber yarns had the greatest influences on performance of the C/C composite, especially on tensile strength.

Effect of manufacturing defects on mechanical properties and failure features of 3D orthogonal woven C/C composites

Rebar corrosion has become a very common cause of degradation in the reinforced concrete structures. It is most frequently the result of the chloride-induced breakdown of the passive film formed in...

Reinforcement corrosion assessment capability of surface bonded and embedded piezo sensors for reinforced concrete structures

The mechanical response of epoxy resin Epon E 863 has been studied in tension, compression, and flexure. The epoxy resins have been tested at different strain rates ranging from 5.9×10-5 to 0.03  s-1. Two types of dog-bone geometries have been used in the tension tests. Small sized cubic, prismatic, and cylindrical samples were used in compression tests. Beams with quarter deep notches or grooves were tested at their midpoints in flexural tests. Strains were measured by using a digital image correlation technique, extensometer, strain gages, and actuator. Observation of sample geometry during tension tests at constant elongation rate shows necking and crazing in Epon E 863. Cubic, prismatic, and cylindrical compression samples undergo a stress drop at yield, but only cubic samples experience strain hardening before failure. Characteristic points of tensile and compressive stress strain relation and load deflection curve in flexure, such as proportional elastic limit stress (PEL), ultimate tensile ...

Characterization of Epoxy Resin Including Strain Rate Effects Using Digital Image Correlation System

A damage assessment methodology using a time–frequency signal processing technique is presented in this article. Delaminations are detected in composite structures with multiple stiffeners. Because Lamb waves are complex in nature, due to wave dispersion and scattering, a robust signal processing technique is required to extract features from Lamb wave signals. In this article, the matching pursuit decomposition algorithm is used for extracting wavelets from the Lamb wave signals in the time–frequency domain. A small time–frequency atom dictionary is defined to avoid the exhaustive search over the time–frequency domain and to reduce the computation costs. The propagation characteristics of Lamb waves in stiffened composite panels are investigated. The delaminations are detected by identifying the converted Lamb wave modes introduced by the structural imperfection. A two-step damage detection approach, which uses both pulse-echo and pitch-catch active sensing schemes, is developed for the identification of...

Damage assessment of CFRP composites using a time–frequency approach:

The scope of this work is to study the effects of manufacturing and installation defects on mechanical performance of polymer matrix composites appearing in civil infrastructure and aerospace applications. The objective of this study is to create a link between defects detected through nondestructive testing (NDT) and the mechanical performance of the composite structures using strain mapping technique. Monotonic tensile samples of polymer matrix stitch-bonded biaxial composite laminates [90,0]s are tested. Flash Thermography, a conventional NDT technique, is used to predict detectable pre-existing surface and sub-surface irregularities and defects. Attention is drawn to the homogenized mechanical behavior and to damage initiation and propagation. Damage onset and propagation are studied using time-dependent nonlinear regression of the strain field. Effects of the manufacturing and installation irregularities on damage initiation, propagation, and failure are monitored as the structure is subjected to load or studied at the end of the loading process.

Damage characterization of surface and sub-surface defects in stitch-bonded biaxial carbon/epoxy composites

Multi-linear stress–strain and closed-form moment curvature response of epoxy resin materials

A piecewise linear parametric uniaxial stress-strain approach has been used to obtain the closed form nonlinear moment curvature response on the basis of strain compatibility in bending for epoxy resin materials. The stress-strain curves, consisting of a bilinear ascending curve followed by strain softening and constant plastic flow in tension and compression, are described by two main parameters, with an additional five nondimensional tensile and seven nondimensional compressive parameters. The main parameters are the modulus of elasticity and strain at the proportional elastic limit point in tension. Parametric studies show that ultimate tensile stress and compressive yield stresses and tension and compression flow stresses have the highest effects on flexural load carrying capacity. Moment curvature equations, in conjunction with softening localization and static equilibrium conditions, were used to simulate the flexural load-deflection response of a beam under three-point bending (3PB) conditi...

https://ascelibrary.org/doi/pdf/10.1061/%28ASCE%29AS.1943-5525.0000133

Masoud Yekani Fard

Papers

Characterization of Epoxy Resin Including Strain Rate Effects Using Digital Image Correlation System

Damage assessment of CFRP composites using a time–frequency approach:

Damage characterization of surface and sub-surface defects in stitch-bonded biaxial carbon/epoxy composites

Multi-linear stress–strain and closed-form moment curvature response of epoxy resin materials

Analytical Solution for Flexural Response of Epoxy Resin Materials