Evaluation Of Internal Damage Research Articles

Thermomechanical and damage characterisation of short glass fibre reinforced polyamide 6 and impact-modified polyamide 6 composites

Polyamide 6 and its composites are widely used in engineering applications that are exposed to high strain rate deformation. This paper investigates the thermomechanical properties of two polyamide 6 composites, both reinforced with 30 wt% short glass fibres, and one of which additionally contains an impact modifier, to provide an understanding of the mechanical response over a wide range of strain rates and temperatures. Compression experiments were performed at rates between 2 and 3000 s−1, with high speed optical and infrared cameras to aid interpretation of the rate-dependent failure arising from the formation of adiabatic shear bands. Further high strain rate experiments were performed with ultra-fast X-ray phase-contrast imaging to provide in-situ internal damage evaluation. These data will improve the utilization of these composites and aid in development of advanced thermomechanical models.

Optical evaluation of internal damage to human hair based on second near-infrared window polarization microscopy.

Hair beauty treatments glorify human life. As a side effect, there is a risk of deteriorating the health of the hair. Optically polarized microscopy has been used for many decades to evaluate hair conditions owing to its ease of use and low operating costs. However, the low biopermeability of light hinders the observation of detailed structures inside hair. The aim of this study is to establish an evaluation technique of internal damages in a hair by utilizing a near-infrared (NIR) light with a wavelength of 1000-1600 nm, called "second NIR window". We built a laser scanning transmission microscope system with an indium gallium arsenide detector, a 1064 nm laser source, and optical circular polarization to visualize the anisotropy characterization of keratin fibres in hair. Samples of Asian black hair before and after bleaching, after permanent-waving, after lithium bromide (LiBr) treatment, and after heating was observed. Some parameters reflecting intra-hair damage were quantitatively compared with the parameters in digitally recorded images with analytical developments. The light transmittance of black hair was dramatically improved by utilizing the second NIR window. Numerical analysis of circular polarization in hair quantified the internal damage in chemically or thermally treated hair and found two different types of damage. The present method enabled quantitative evaluation of the condition changes in the cortex; for example, a decrease in circular polarizability by LiBr treatment and restoration by replacing the LiBr solution with water. In addition, black speckles were observed after the heat treatment. Longer heating and wetting times increased the appearance probability and size of the speckles. According to quantitative analyses, the emergence of black spots was independent of polarizability changes, indicating that they were not pores. Circular polarization microscopy based on near-infrared optics in the second NIR window provides an effective evaluation method for quantifying intra-hair damage caused by cosmetic treatments. The present method provides noninvasive, easy, and inexpensive hair evaluation and has potential as a gold standard in hair care research/medical fields.

Evaluation of Internal Damage in Concrete Structure by Means of Elastic Wave Tomography

Evaluation of Internal Damage in Concrete Structure by Means of Elastic Wave Tomography

Three-dimensional damage quantification of low velocity impact damage in thin composite plates using phased-array ultrasound

The evaluation of internal damage in multilayered composite materials is of great importance for high reliability-demanding applications, and remains a challenge due to the complex failure modes and mechanism of composite materials. This study presents a volumetric method of three-dimensional size quantification and prediction for low velocity impact damage in thin composite plates using phased-array ultrasound. A set of low velocity impact damages are induced in thin carbon fiber/epoxy resin matrix composite plates using quasi-static indentation tests. A volumetric reconstruction method is proposed to reconstruct a three-dimensional volume from the raw data, allowing for direct damage identification, localization, and quantification. Using the echo amplitude feature of the reconstructed volume, the 6 dB-drop method is employed to characterize the damage size in terms of volumes and areas. An impact size prediction model is established to correlate the impact energy and the damage volume/area. Comparisons are made between the microscopy measurement of the damage cross-section and results obtained using the developed method.

Safe pHRI via the Variable Stiffness Safety-Oriented Mechanism (V2SOM): Simulation and Experimental Validations

Robots are gaining a foothold day-by-day in different areas of people’s lives. Collaborative robots (cobots) need to display human-like dynamic performance. Thus, the question of safety during physical human–robot interaction (pHRI) arises. Herein, we propose making serial cobots intrinsically compliant to guarantee safe pHRI via our novel designed device, V2SOM (variable stiffness safety-oriented mechanism). Integrating this new device at each rotary joint of the serial cobot ensures a safe pHRI and reduces the drawbacks of making robots compliant. Thanks to its two continuously linked functional modes—high and low stiffness—V2SOM presents a high inertia decoupling capacity, which is a necessary condition for safe pHRI. The high stiffness mode eases the control without disturbing the safety aspect. Once a human–robot (HR) collision occurs, a spontaneous and smooth shift to low stiffness mode is passively triggered to safely absorb the impact. To highlight V2SOM’s effect in safety terms, we consider two complementary safety criteria: impact force (ImpF) criterion and head injury criterion (HIC) for external and internal damage evaluation of blunt shocks, respectively. A pre-established HR collision model is built in Matlab/Simulink (v2018, MathWorks, France) in order to evaluate the latter criterion. This paper presents the first V2SOM prototype, with quasi-static and dynamic experimental evaluations.

Random forest-based evaluation technique for internal damage in reinforced concrete featuring multiple nondestructive testing results

The evaluation of internal damage in concrete structures is related to not only its rapid repair and reinforcement but also its safe usage, and is therefore essential for ensuring its longevity. This paper proposes a method to evaluate the extent of internal damage due to rebar corrosion using Random Forest, one of the supervised machine learning methods. In supervised machine learning, appropriate inputs should be identified to obtain accurate results. This research uses air permeability coefficient, electrical resistivity, ultrasonic velocity, and compressive strength which is obtained by nondestructive tests as inputs. In order to acquire a large number of data for the training, the rebar corrosion was promoted by electrolytic corrosion, and the data was frequently acquired. Then, the high accuracy of the model was confirmed by cross-validation. In addition, the proposed method was applied to the inspection of actual bridges, and it can detect internal damage that is otherwise invisible on the exterior surface.

V2SOM: A Novel Safety Mechanism Dedicated to a Cobot’s Rotary Joints

Unlike “classical” industrial robots, collaborative robots, known as cobots, implement a compliant behavior. Cobots ensure a safe force control in a physical interaction scenario within unknown environments. In this paper, we propose to make serial robots intrinsically compliant to guarantee safe physical human–robot interaction (pHRI), via our novel designed device called V2SOM, which stands for Variable Stiffness Safety-Oriented Mechanism. As its name indicates, V2SOM aims at making physical human–robot interaction safe, thanks to its two basic functioning modes—high stiffness mode and low stiffness mode. The first mode is employed for normal operational routines. In contrast, the low stiffness mode is suitable for the safe absorption of any potential blunt shock with a human. The transition between the two modes is continuous to maintain a good control of the V2SOM-based cobot in the case of a fast collision. V2SOM presents a high inertia decoupling capacity which is a necessary condition for safe pHRI without compromising the robot’s dynamic performances. Two safety criteria of pHRI were considered for performance evaluations, namely, the impact force (ImpF) criterion and the head injury criterion (HIC) for, respectively, the external and internal damage evaluation during blunt shocks.

Vibration-Based Non-Destructive Evaluation of Internal Damage in Foam Cored Sandwich Structures Using Wavelet Analysis

Modern mechanical and civil structures are increasingly designed using polymeric composites that ensure great strength-to-mass ratio and are resistant to various environmental interactions, like corrosion. The application of sandwich structures in the design of mechanical and civil constructions is determined by their good stiffness properties and very low mass, which is a very attractive combination. Due to their wide applicability, these structures should be properly maintained and diagnosed, and thus, appropriate non-destructive testing (NDT) methods should be developed in order to detect and identify various types of damage. Special attention should be paid to internal damage (damage to the core of a sandwich structure), which cannot be detected during a visual inspection. In the paper, an NDT method based on modal analysis and further processing of modal shapes using a wavelet transform is proposed. Three sandwich structures with damage to the core of various types were experimentally tested using modal analysis, the damage positions were detected and identified using wavelet analysis, and verified by comparing the results of previously performed thermographic tests. The obtained results show a high effectiveness of the proposed approach, which could find an application in the industrial inspection of sandwich structures in a non-destructive and non-contact manner.

Internal damage evaluation of composite structures using phased array ultrasonic technique: Impact damage assessment in CFRP and 3D printed reinforced composites

The application of non-destructive techniques for the evaluation of internal damage in composite materials is a challenge due to their complexity. The aim of this study is to analyse the ability of ultrasonic technique to identify and evaluate manufacturing defects and internal damage in composite laminates. Artificial object inclusions of different shapes, sizes and materials were embedded in carbon fibre reinforced epoxy (CFRP) laminates. Comprehensive investigation of non-destructive evaluation using phased array ultrasonic testing to trace and characterize the embedded defects is presented. Phased array ultrasonic technique was able to precisely locate most of the artificial inclusion in the composite laminates. Nerveless, the shape and size of the inclusions were not accurately determined due to the high signal attenuation and distortion characteristics of the carbon fibre epoxy composite.Furthermore, a major concern affecting the efficient use of composite laminates is their vulnerability to low velocity impact damage. The dynamic behaviour of composite laminates is very complex as there are many concurrent phenomena during composite laminate failure under impact loading. Thus, the practicality of the previous results is demonstrated by the evaluation of impacted carbon fibre reinforced epoxy laminates using ultrasonic testing. The influence of laminate thickness and impact energy on impact damage is also investigated. The performance of phased array ultrasonic testing for the inspection of composite laminates with barely visible impact damage is evaluated. In addition, fibre-reinforced thermoplastic composites are becoming more significant in industrial applications due to their excellent mechanical performance and potential recycling. In this study, impact damage in 3D printed continuous glass fibre reinforced thermoplastic laminates is also analysed. Phased array ultrasonic testing is performed and the amount of damage is quantified in terms of delaminated area.

The fatigue damage evaluation of gear in sugarcane presser using higher order ultrasonic nonlinear coefficients

Abstract The fatigue damage of gear in sugarcane presser is one of the most common damages, which is very difficult to detect in sugar factory. The nonlinear ultrasonic technique is used to evaluate the fatigue damage of gear in this paper. The perturbation method is applied to solve the nonlinear wave equation, the relationship between relative nonlinear coefficient and higher harmonics is analyzed which the second and third order relative nonlinear coefficients are applied to evaluate the fatigue damage. The gear in sugarcane presser after three years service is the research objective, which thirty-two points at tooth root and sixteen points at tooth centre are conducted the nonlinear ultrasonic experiment. Experimental results indicate different detection points have different damage degree, and the fatigue damage degree of tooth No. 14 and 15 are more serious than other teeth. While for the same tooth, the damage degree of tooth root is much severer than the tooth centre. Therefore, the measured relative nonlinear coefficients could be applied to evaluate the fatigue damage of gear, which provides the practical method for internal damage evaluation of gear in sugar factory.

Damage evaluation of an internal concrete in steel-plate bonded slabs with anchor-bolts

Re-deterioration is currently found in reinforced concrete (RC) slabs of highways, which were retrofitted with steel-plates. However, the presence of asphalt pavement and steel-plates covering the top and bottom surfaces of the slabs makes it extremely difficult to determine internal damage of concrete. The damage could significantly affect the load carrying capacity and the durability of the whole structure. In this study, a novel technique for proper inspection and evaluation is proposed, by applying the temporary anchors left on the steel-plates bonded as sensing probes. An impact is driven by hammering the head of anchor bolt, which is employed as a sensing probe to detect elastic waves through RC slabs. By focusing on the characteristic frequency band of the Rayleigh waves, the arrival time and the associated velocity are to be evaluated. An inspection was carried out on an existing bridge in service for the verification of the sensing technique. It is found that the anchor-bolt sensing technique proposed is applicable to evaluation of internal damage of concrete slabs retrofitted with steel-plates.

Fundamental mechanical behaviors of dental restorative materials resin composites due to compressive and flexural loading and internal damage evaluation

Development of internal damage within resin composites was evaluated under compressive loading in order to predict crack initiation and fracture. Moreover, three-point bending tests were also carried out in order to clarify mechanical behavior and fracture under tensile stress state in comparison with those under compressive stress state. Both of them were conducted for the purpose of obtaining data to formulate constitutive equations for resin composites and to implement precise numerical simulation. Columnar specimens for compression tests and square pole specimens for three-point bending tests were prepared by using clinical resin composites. In compression tests, loading–unloading (or –reloading) was given to columnar specimens and Young’s modulus was evaluated by the gradient of stress–strain curves under unloading. Internal damage was evaluated from the variation of Young’s modulus as a scalar damage variable based on the continuum damage mechanics. The variation of apparent density and residual strain at vanished stress were also discussed in association with the development of internal damage. Accumulation of internal damage was found on the stress–strain curve under loading–unloading–reloading in comparison with the curve under monotonic loading. On the other hand, in three-point bending tests, dependence of stress–strain curves on light curing time and strain rate was clarified. Since compression tests have been carried out under similar experimental conditions by authors so far, mechanical behaviors of resin composites under tensile stress state were discussed in comparison with those under compressive stress state. Brittleness under tensile stress state was indicated in comparison with compressive stress state.

OS0704 歯科修復用コンポジットレジンの静的荷重による変形特性と内部損傷評価

OS0704 歯科修復用コンポジットレジンの静的荷重による変形特性と内部損傷評価

Fatigue life of piezoelectric ceramics and evaluation of internal damage

Compression-compression fatigue tests were performed for PZT piezoelectric ceramics by using columnar specimens at various frequencies of cyclic loading. In fatigue tests, stress ratio was fixed to R=0.05, and maximum compressive stress was changed. A damage variable based on the continuum damage mechanics was evaluated by variation of apparent density of specimens. Moreover, area fraction of cavities on fracture surface was evaluated. As a result of experiments, the dependence of fatigue life on frequency of cyclic loading was clarified. It was also found that the damage variable is independent of the frequency, while the area fraction of cavities depends on the frequency.

음향방출법을 응용한 복합재 날개 구조물의 정적구조 건전성 평가

복합재 날개 구조물에 대한 구조 건전성 및 손상을 평가하기 위하여 정적 구조강도시험에 음향방출(AE)법이 응용되었다. 시험중 스트레인과 변위측정기법을 통하여 정적구조강도를 확인하였고, 음향방출요소 분석과 위치표정기법을 통하여 구조물의 내부 손상을 평가하고 손상위치를 찾을 수 있었다. 시험은 설계제한하중시험, 2차에 걸친 설계극한 하중시험, 파단시험이 수행되었다. 주요한 AE신호는 front lug근처의 표면에 부착된 센서에 의하여 감지되었다. 특히 1차 설계극한하중시험에서 스트레인 및 변위결과는 내부 손상을 보이지 않았으나 AE신호는 내부 손상이 이미 형성된 현상을 나타내었다. 파단시험에서는 AE활성도가 매우 활발하였고, 스트레인 및 변위의 결과는 심한 손상에 의하여 하중경로가 바뀌는 경향을 나타내었다. 음향방출법을 적용하여 정적 구조시험이 진행되는 동안 내부손상이 발생되는 하중과 위치를 정확하게 평가할 수 있었다. 본 연구로부터 음향방출법은 정적 구조강도시험에 있어 내부 손상을 평가하는데 유용한 기법임이 확인되었다. AE technique was applied to the static structural test of the composite wing structure to evaluate the structural integrity and damage. During the test, strain and displacements measurement technique were used to figure out for static structural strength. AE parameter analysis and source location technique were used to evaluate the internal damage and find out damage source location. Design limit load test, the 1st and 2nd design ultimate load tests and fracture test were performed. Main AE source was detected by an sensor attached on skin near by front lug. Especially, at the 1st design ultimate test, strain and displacements results didn't show internal damage but AE signal presented a phenomenon that the internal damage was formed. At the fracture test, AE activities were very lively, and strain and displacements results showed a tendency that the load path was changed by severe damage. The internal damage initiation load and location were accurately evaluated during the static structural test using AE technique. It is certified from this paper that AE technique is useful technique for evaluation of internal damage at static structural strength test.

Variation of Material Properties of Piezoelectric Ceramics due to Mechanical Loading and Evaluation of Internal Damage

In the present paper, lead zirconate titanate (PZT) piezoelectric ceramics were subjected to compressive mechanical loading, and static and fatigue fracture tests were performed. Each test was interrupted systematically after applying prescribed loading, and resonance and anti-resonance frequencies and an electrostatic capacity were measured by means of an impedance analyzer. Then an electromechanical coupling coefficient, a dielectric constant, an elastic coefficient and a piezoelectric constant as material properties of piezoelectric ceramics were evaluated from them. The variation of the material properties due to static and cyclic compressive loading was investigated experimentally. Further, since internal damage of materials affects their material properties, the damage was evaluated reversely from the variation of the elastic coefficient in the present paper. Then the development of internal damage due to mechanical loading was clarified on the basis of the continuum damage mechanics. From SEM micrograph of the fracture surface, it was found that the damage was microscopic cracks in the direction of compressive loading.

IMPACT DAMAGE EVALUATION OF FIBRE-REINFORCED COMPOSITE MATERIALS AND STRUCTURES

An overview is presented of destructive and nondestructive techniques that have been widely used to characterize impact damage in fibre reinforced composites. Particular emphasis is placed on in-depth study of the radiography and ultrasonic methods as the means of quantitative evaluation of internal damage in fibre composite structures. The operating principles of these techniques are described along with advantages and disadvantages in their applications. This paper highlights the chapter contributed by the author to the book.

Avaliação da qualidade de sementes de Eugenia pleurantha (Myrtaceae) pelo teste de raios X

O teste de raios X é uma ferramenta útil para avaliar a qualidade física de sementes florestais, que pode ser afetada pela ocorrência de sementes vazias, infestação por insetos e alterações físicas. Objetivou-se, com este estudo, verificar a eficiência do teste de raios X na avaliação dos danos internos em sementes de Eugenia pleurantha, bem como examinar a conseqüência destes danos na germinação. Sementes de Eugenia pleurantha foram colocadas em suportes de isopor e expostas a diversas intensidades de radiação (35, 45, 50 e 60 Kvp), com duração de 45 e 60 segundos para determinar o padrão de raios X. De acordo com a anatomia visualizada nas radiografias, as sementes foram classificadas em Sementes Cheias e Sementes Infestadas. Em seguida, as sementes foram submetidas ao teste de germinação em substrato sobre areia a 30ºC sob luz branca constante. A intensidade de radiação de 50 Kvp no tempo de exposição aos raios X de 60 segundos permitiu a visualização nítida dos danos internos causados por infestação de insetos nas sementes. Os danos internos causados por larvas observados nas radiografias impedem a germinação das sementes de Eugenia pleurantha.

A Numerical Model for the Freeze-Thaw Damages in Concrete Structures

This paper deals with the accumulated damage in concrete structures due to the cyclic freeze-thaw as an environmental load. The cyclic ice body nucleation and growth processes in porous systems are affected by the thermo-physical and mass transport properties, and gradients of temperature and chemical potentials. Furthermore, the diffusivity of deicing chemicals shows significantly higher value under cyclic freeze-thaw conditions. Consequently, the disintegration of concrete structures is aggravated at marine environments, higher altitudes, and northern areas. However, the properties of cyclic freeze-thaw with crack growth and diffusion of chloride ion effects are hard to be identified in tests, and there has been no analytic model for the combined degradations. The main objective is to determine the driving force and evaluate the reduced strength and stiffness by freeze-thaw. For the development of computational model of those coupled deterioration, micro-pore structure characterization, pore pressure based on the thermodynamic equilibrium, time and temperature dependent super-cooling with or without deicing salts, nonlinear-fracture constitutive relation for the evaluation of internal damage, and the effect of entrained air pores (EA) has been modeled numerically. As a result, the amount of ice volume with temperature dependent surface tensions, freezing pressure and resulting deformations, and cycle and temperature dependent pore volume has been calculated and compared with available test results. The developed computational program can be combined with DuCOM, which can calculate the early aged strength, heat of hydration, micro-pore volume, shrinkage, transportation of free water in concrete. Therefore, the developed model can be applied to evaluate those various practical degradation cases as well.

An image analysis technique for evaluating internal damage in graphite-fabric/polyimide composites

The purpose of this paper is to suggest a possible technique for evaluating internal damage in fabric-reinforced composite materials. The technique presented in this work is based on capturing and performing a qualitative analysis of scanning electron microscope (SEM) images of damage from planar specimen slices (serial sections) and then reassembling the slices in three-dimensional space. This method has been applied to evaluating damage in graphite-fabric/PMR-15 Iosipescu specimens tested in shear. Three-dimensional damage maps have been presented and the extent of damage through the thickness of a graphite-fabric/PMR-15 losipescu specimen has been determined. The same approach could be used for the evaluation of internal damage in other composite systems.