Analysis of Detection of Delaminations in Fiber Reinforced Composite Tubes Using Axially Symmetric Guided Waves

The current and proposed use of fiber reinforced composite tubes in a number of aerospace structural applications is well established. The most serious hindrance to acceptance of composites, in general, is the need to certify non-destructively the integrity of the material [1]. The modes of damage in a composite are varied and complex. Delaminations are particularly important, representing an advanced state of damage in the material [2,3]

Damage signature of fatigued fabric reinforced plastics in the pulsed ultrasonic polar scan

This study investigates the use of both the amplitude and time-of-flight based pulsed ultrasonic polar scan (P-UPS) for the nondestructive detection and evaluation of fatigue damage in fiber reinforced composites. Several thermoplastic carbon fabric reinforced PPS specimens (CETEX), loaded under various fatigue conditions, have been scanned at multiple material spots according to the P-UPS technique in order to extract material degradation in a quantitative way. The P-UPS results indicate that shear dominated fatigued carbon/PPS goes with a reduction of shear properties combined with large fiber distortions. The P-UPS results of the tension-tension fatigued carbon/PPS samples on the other hand reveal a directional degradation of the stiffness properties, reaching a maximum reduction of -12.8% along the loading direction. The P-UPS extracted damage characteristics are fully supported by simulations, conventional destructive tests as well as visual inspection. The results demonstrate the excellent capability of the P-UPS method for nondestructively assessing and quantifying both shear-dominated and tension-tension fatigue damage in fabric reinforced plastics

On the difficulty of greedy tetrahedralization of points in 3-D

Limitations of ceramic materials such as brittleness, low tensile strength and low fracture toughness are being overcome with the introduction of ceramic matrix composites. The mechanical behavior of these fiber-reinforced composites strongly depends on the fiber-matrix bonding condition. If the bonding is too weak, there is poor stress transfer. On the other hand, for a case of very strong bond, the material behaves in a brittle fashion. Recently, photomicroscopic observations were made and the macroscopic behavior of the material was related to the failure mechanisms and damage development under loading [1]. However, this method is destructive, limited to damage on the surface only and cannot easily detect fiber-matrix debonding. Since fiber-matrix debonding is an important indicator of material response it is important to investigate it nondestructively. An effort was made to correlate macroscopic response with microscopic observations and real-time ultrasonic measurements in a unidirectional silicon carbide/glass ceramic composite under longitudinal tensile loading [2]

A Homomorphic Deconvolution Technique For Improved Ultrasonic Imaging Of Thin Composite Laminates

INTRODUCTION Advanced composites, particularly high modulus laminates, are often susceptible to transverse impact loading. The major damage introduced due to low velocity impact includes matrix cracking, fiber break and delaminations. Such flaws tend to reduce residual strength of the material and may cause structural failure when the material is subjected to higher operating loads [1, 2]. Unfortunately, such a damage cannot be observed on the surface until failure; hence, structural integrity should be assessed by nondestructive evaluation (NDE) methods at the earliest possible stage. Conventional ultrasonic pulse-echo C-scan methods have been widely used for detecting delaminations in composites. More recently, a three-dimensional imaging technique has been developed for full-volume evaluation of impact and other types of damage [3]. All of these methods use broadband ultrasonic signals analyzed in the time-domain using either gated peak detectors or digitized A-scan waveforms. The

Three-Dimensional Imaging of Impact Damage in Composite Laminates

Conventional ultrasonic C-scanning for detection and characterization of material defects has limitations because it provides only an overall planar view of the damage without accurate definition of the size and location of flaws. Hence, a three-dimensional reconstruction from the digitized ultrasonic pulse-echo waveform database was developed for full volume evaluation of damage [1]

Determination of Angular Parallaxes between the Geometric Coordinate System and the Material Symmetry Coordinate System of Anisotropic Materials

The hypothesis of an orthorhombic symmetry and the knowledge of the material symmetry axes is usually necessary to characterize a medium by ultrasonic techniques [1–5]. However a wrong setting up of the sample or the strata’s stacking defects in industrial composite material lead to the non-superposition between the material symmetry coordinate system and the observation coordinate system. The development of a procedure to identify elasticity coefficients for materials that have no more symmetry planes, is necessary.</p