Nondestructive testing of composites using a nonlinear acoustic spectroscopy method

The presented experimental work describes the nondestructive examination of polymer based composites using an acoustic method under the consideration of nonlinear effects. The technique is based on the fact that material behaves more nonlinearly in the presence of damage than in the undamaged state during dynamic load. Damaged structures show an increased nonlinear transmission behavior. Consequently, the level of nonlinearity is an indication of the damage severity. The aim is to analyze the nonlinear transfer behavior and if a quantification can be used to determine the damage severity. The focus is on the type of nonlinear acoustic spectroscopy methods that analyses the modulation spectrum. When two harmonic waves are applied with different frequencies to a damaged material, the amplitude of the high-frequency wave will be modulated by the low-frequency wave and the created spectrum manifests an intermodulation by showing new frequencies such as sidebands and higher harmonics. Samples made of glass fiber reinforced vinyl ester respectively epoxy, both taffeta woven, and pre-damaged by application of tensile tests using different levels of tension have been considered. A new experimental setup has been developed and a clearly visible increase of the intermodulation with increasing damage has been noticed for both materials. Finally, the method is proven to nondestructively evaluate the damage state of composites.OpenLab “Materials and Processes” supported by PSA Peugeot Citroë

Damage Evaluation in Woven Glass Reinforced Polyamide 6.6/6 Composites Using Ultrasound Phase-Shift Analysis and X-ray Tomography

The paper proposes a new experimental methodology, based on ultrasonic measurements, that aims at evaluating the anisotropic damage in woven semi-crystalline polymer composites through new damage indicators. Due to their microstructure, woven composite materials are characterized by an anisotropic evolution of damage induced by different damage mechanisms occurring at the micro or mesoscopic scales. In this work, these damage modes in polyamide 6.6/6-woven glass fiber reinforced composites have been investigated qualitatively and quantitatively by X-ray micro-computed tomography (mCT) analysis on composite samples cut according to two orientations with respect to the mold flow direction. Composite samples are initially damaged at different levels during preliminary interrupted tensile tests. Ultrasonic investigations using C-scan imaging have been carried out without yielding significant results. Consequently, an ultrasonic method for stiffness constants estimation based on the bulk and guided wave velocity measurements is applied. Two damage indicators are then proposed. The first consists in calculating the Frobenius norm of the obtained stiffness matrix. The second is computed using the phase shift between two ultrasonic signals respectively measured on the tested samples and an undamaged reference sample. Both X-ray mCT and ultrasonic investigations show a higher damage evolution with respect to the applied stress for the samples oriented at 45◦ from the warp direction compared to the samples in the 0◦ configuration. The evolution of the second ultrasonic damage indicator exhibits a good correlation with the void volume fraction evolution estimated by mCT as well as with the damage calculated using the measured elastic modulus reduction. The merit of this research is of importance for the automotive industry.The present work was funded by PSA Group and made in the framework of the OpenLab Materials and Processes. This OpenLab involves PSA Group, The Arts et Metiers ParisTech and Georgia Tech Lorraine

Detection and evaluation of barely visible impact damage in woven glass fabric reinforced polyamide 6.6/6 composite using ultrasonic imaging, X-ray tomography and optical profilometry

The present experimental work investigates the response of woven glass fabric reinforced polyamide 6.6/6 subjected to drop weight impact loading. The main objective is the development and the introduction of a new experimental procedure/approach, based on different complementary detection techniques, that aims at investigating the damage induced by impact loading in thermoplastic woven fabric composites. The developed approach is intended to be generalized to other types of composite materials. The main idea is to assess all the experimental results obtained through the developed procedure with a direct investigation method. The latter consists in the Permanent Indentation (PI) measurement providing an indicator of the damage criticality in the composite sample. To this end, several non-destructive testing methods are carried-out and their experimental findings are analyzed and cross-linked. The identification of the different damage mechanisms, caused by the drop weight impact, is performed using X-Ray micro-computed tomography (mCT). C-scan ultrasonic investigation is conducted according to two types: transmission and reflection for the detection of the impact damage and the identification of the induced degradation area. B-scan imaging are then obtained through specific post-processing of the impacted surface to extract the permanent indentation (PI). The latter is validated through surface flatness measurement using the highly resolved 3D optical profilometry. The correlation between the X-Ray tomography results and the permanent indentation measurement is then established. It correlates the PI level with the damage mechanisms of a barely visible impact damage (BVID) in woven glass reinforced polyamide 6.6/6 composite.The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: The present work is co-funded by Groupe PSA and ANRT. It is made in the framework of the OpenLab Materials and Processes involving Groupe PSA, Arts et Metiers (ENSAM) and Georgia Tech Lorraine

Application of Ultrasonic Coda Wave Interferometry for Micro-cracks Monitoring in Woven Fabric Composites

The consequences of a four-point bending test, up to 12 mm, are examined by emitting 1 MHz ultrasonic guided waves in woven carbon fiber reinforced polymer specimens, using coda wave interferometry (CWI), revealing a potential use for nondestructive evaluation. It is known that CWI is more sensitive to realistic damage than the conventional method based on the first arriving time of flight in geophysical, or in civil engineering applications such as concrete structures. However, in composite materials CWI is not well established because of the involved structural complexity. In this paper, CWI is investigated for monitoring the occurrence of realistic defects such as micro-cracks in a woven carbon fiber composite plate. The micro-cracks are generated by a four-point bending test. The damage state is stepwise enhanced by gradually increasing the load level, until failure initiation. The damage is monitored, after each loading, using ultrasound. It is demonstrated that CWI is a powerful tool to detect damage, even low levels, in the sample. Two damage indicators based on CWI, i.e. signals correlation coefficient and relative velocity change, are investigated and appear to be complimentary. Under significant loading levels, the normalized cross-correlation coefficient between the waveforms recorded in the damaged and in the healthy sample (reference at 0 mm), decreases sharply; this first indicator is therefore useful for severe damage detection. It is also demonstrated, by means of a second indicator, that the relative velocity change between a baseline signal taken at zero loading, and the signals taken at various loadings, is linear as a function of the loading, until a critical level is reached; therefore this second indicator, is useful for low damage level detection. The obtained evolution of the relative velocity measurement is supported by relative comparison to the evolution of the bending modulus in function of displacement. The relative velocity change exhibits the same evolution as the bending modulus with loading. It could be used to indicate when the material stiffness has decreased significantly. The research is done in the framework of composite manufacturing quality control and appears to be a promising inspection technique.This work is supported by the Région Grand Est

Investigation of Damage in Composites Using Nondestructive Nonlinear Acoustic Spectroscopy

International audienceThe presented experimental work describes the nondestructive damage examination of polymer-matrix composites using acoustic methods under the consideration of nonlinear effects. The aim is to analyze these nonlinear effects in order to provide a quantification of the nonlinear acoustic transmission which is related to the damage state and its severity in the composite material. The first objective was to study the effectiveness of the distortion evaluation method and its related parameter: the BTotal Difference Frequency Distortion^ (TDFD) parameter. The TDFD was utilized as a new damage indicator to quantify the progressive damage state in composite materials. The TDFD method had initially been proposed to characterize the distortion of audio amplifiers. A custom-made setup was developed that imposes acoustic signals to the structure. The samples’ vibrations were afterwards analyzed by a laservibrometer and further spectrum evaluations. The developed method was applied to two composite materials, both reinforced with taffeta woven glass-fibers, but having different thermoset polymer matrix, i.e. vinylester and epoxy. The damage was introduced in the specimen by tensile tests with a stepwise increase of the tension loading. It was observed that damage influences the intensity of nonlinear intermodulation after having introduced two harmonic and constant signals of different and randomly chosen frequencies in the specimen. The nonlinear intermodulation was then quantified by computing the TDFD parameter. In the specific case of epoxy based composites, high frequency peaks were noted for the high tensile loading levels only. The TDFD parameter was then modified in order to take into account this effect. For both studied composites, the modified TDFD parameter increases with the damage accumulation caused by the applied stepwise tensile loading

Detection and evaluation of anisotropic damage with ultrasonic method in a glass woven fabric reinforced polyamide PA 66/6/ composite

Un composite polyamide 66/6 renforcé par un tissu à armature sergée de 2,2 en fibres de verres a été étudié par une méthode ultrasonore avancée. Les mécanismes d’endommagement de ce type de matériau dépendent de la nature de sollicitation et de l’architecture du renfort, en particulier de l’orientation des fibres. Dans ce travail, une sollicitation en traction a été considérée pour deux configurations d’orientation des éprouvettes : (i) orientée suivant la direction d’écoulement (sens du renfort chaine) et (ii) orientée à 45° de celle-ci. Différents niveaux d’endommagement ont été induis pour ces deux configurations d’échantillons, jusqu’à des niveaux proches de la rupture. Une première estimation de l’endommagement est obtenue à travers la baisse du module d’élasticité et sert de référence. Pour chaque niveau d’endommagement, une méthode ultrasonore de mesure du tenseur de rigidité est ensuite utilisée sur chaque échantillon. Un schéma différent d’évolution anisotrope de l’endommagement a été observé pour chaque configuration d’échantillon. A partir des signaux obtenus par mesure ultrasonore, un nouvel indicateur d’endommagement a été proposé. Cet indicateur est basé sur la mesure de déphasage du signal ultrasonore par rapport à un signal obtenu sur éprouvette non endommagée. Le nouvel indicateur s’est révélé plus sensible à la dégradation du matériau comparativement à l’indicateur d’endommagement classique fondé sur la réduction du module d’élasticité. Les deux indicateurs ont montré une évolution importante de l’endommagement lors de chargement en traction à 45°de la direction d’écoulement gouverné par un mode de cisaillement.In this study a polyamide 66/6 based composite reinforced with twill woven glass fabric is investigated using an advanced ultrasonic method. It is well established that the damage scheme of those of composites depends on both applied loading and fiber’s orientations. Tensile tests on samples oriented (i) along the mold flow direction and (ii) at 45° of this direction were performed. Increasing stress levels were applied on those two samples configurations until composite final failure. A stiffness constants measurement using ultrasound is then carried out for each applied stress level. Different damage schemes were observed for the two samples configuration. Based on the transmitted ultrasonic signals acquisitions a new damage indicator is proposed. It is based on the phase shift between the signal measured on a damaged sample and the signal from a reference sample. The new ultrasonic damage indicator is proven to be highly sensitive to the material degradation. It has been compared to the classical damage indicator based on the modulus reduction measured during tensile tests. Due to predominance of shear stress, both damage indicators exhibit a higher evolution for the samples oriented at 45° than those oriented at 0°

Assessing the number of twists of stranded wires using ultrasound

Wiring, of different degrees of complexity, is a dominant part of mechanical support in constructions, electromagnetic and telecommunication signal transmission cables, among other applications. Single and manifold twisted wires are prominent examples of such utilities and are susceptible to mechanical irritations and deterioration. They require ultrasonic non-destructive testing and health monitoring. The objective is to develop an ultrasound-based technique to automatically measure the number of twists per meter in winded wire strands implementable in the industry, to be used during an ultrasonic scan and provide the number of twists per meter during cable production, for instance, to verify that calibration is still in place. Fourier transformation is applied as an expedited non-destructive testing method of twisted wires. Digital signal processing to obtain spatial and time spectral representation recognition due to amplitude variance, induced by the varying distance between the transducer and wire, is developed depending on the number of twists. Two different spatial spectral analyses satisfactorily quantify the number of twists by providing the distance between each twist. The method is robust and applicable when the distance between the transducer and strand is not constant, as the industry requires

Monte-Carlo Localization on Metal Plates Based on Ultrasonic Guided Waves

Due to travel restrictions after the CoVid-19 pandemic, the dates have been postponed to a later time in Summer 2021. A final decision about the format of the symposium is expected by late March.International audienceIn this work, we propose a method based on a particle filter for the localization of an industrial robot on a large metal structure that leverages first-order reflections of acoustic waves on metal plate's edges. In our approach, the acoustic measurements are acquired in a (pseudo) pulse-echo mode using a co-localized emitter/receiver pair of piezoelectric transducers. The acquisition of data is done manually but it is aimed to be performed by a robot in the future. A known size of the metal plate is assumed