Stages Of Damage Evolution Research Articles

Response mechanisms of reinforced concrete panels to the combined effect of close-in blast and fragments: An integrated experimental and numerical analysis

The effect of cased explosives on reinforced concrete components is important for the design of protective structures, since the interaction between the fragments and blast waves can modify or even amplify the damage caused. This work deals with the development of finite element analysis techniques to simulate the combined loading and to understand this interaction. In this work, an experiment conducted with a cased explosive and further tests from the literature were used together to develop and stepwise validate finite element analysis models of the different loading phases. The casing fragment velocities and spatial distribution were derived from explosive expansion simulations of the hull using the smooth particle hydrodynamics method together with a momentum conserving penalty contact. The blast loading applied on the concrete plate was based on established empirical formulae, acting at the same times as the fragments. Comparing the final damage with the experimental records revealed good agreement for most damage patterns. The model was used to identify the different damage evolution stages, such as shock-induced shear plug formation and subsequent structural dynamic bending with the associated damage. In addition, differential model variants with fragment and blast loading in isolation were simulated to resolve the response and damage of each loading component. The blast load caused predominantly bending deformations and damage, while the fragments caused similar cratering as seen in the combined case. However, the final combined damage was larger than that caused by each phenomenon. In the given situation, the fragments created most damage, but the established modelling approach opens the perspective to study these effects also for other ratios of explosive to casing weight and scaled distances, where the contributions might differ. Establishing a valid modelling approach is thus an important step towards more insight into the interaction of these complex loading types and damage effects.

Investigating fatigue life prediction of rubber asphalt mixture based on damage evolution using residual strain analysis approach

This study aims to develop the fatigue life (Nf) prediction method of rubber asphalt mixture based on residual strain (RS) analysis by using three-point bending fatigue test. The RS mechanical model established based on the modified Burgers model was used to characterize the evolution laws of RS, the residual viscoelastic strain (RVES) and the residual viscous-flow strain (RVFS), and the mechanical parameter of residual strain ratio (RSR) was defined based on the evolution laws. The correlation analysis was performed to explore the relationship between the Nf and the RSR, and the damage indication was advanced. The damage variable was defined based on the RSR evolution and the established fatigue damage model based on the ExpAssoc damage evolution model was used to perform the damage evolution analysis. The correlation analysis between the RSR and the damage evolution speed (Ds) was conducted to establish the fatigue and remaining fatigue equations. The results showed that RS mainly consisted of RVES and RVFS, and the RVFS was primarily responsible for the material damage. The RS mechanical model can characterize the non-linear evolution laws of RS, RVES and RVFS with sufficient accuracy, and the RVES can be regarded as a constant under given conditions. The RSR characterizing Ds can determine damage evolution and Nf prediction, and define the damage variable by isolating the damage factor from the viscoelastic factor. The established damage model can be capable of capturing the damage evolution of the rubber asphalt mixture. The increased Ds led to the exhibited decrease in the Nf. The established fatigue equation and remaining fatigue equation succeeded in accurately predicting the Nf and remaining fatigue life (Nfr) corresponding to the early damage evolution stage of rubber asphalt mixture, respectively.

Multiple damage mechanisms facilitated by planar dislocation glide in a commercial-grade precipitation-strengthened Fe–Ni–Cr-based steel

The present study addresses the damage evolution mechanism in precipitation-strengthened Fe–Ni–Cr-based steel (SUH 660) at ambient temperature in air. Specifically, damage quantification and associated microstructure characterization were performed. The damage initiation sites were inclusion and grain boundaries impinging dislocation slip. The early stage of damage evolution was observed before necking of the specimen. Subsequent plastic straining caused damage growth along slip planes and coalescence of damage via localized shear in ligaments between damages, for which the behavior was associated with the planar character of the slip. The damage evolution behavior observed in the post-mortem specimen was consistent with fractographic characteristics.

Development and application of a miniaturized tensile testing device for in situ synchrotron microtomography experiments

The nondestructive nature of X-ray microtomography (µCT) associated with its suitable temporal resolution, obtained with the use of high energy polychromatic radiation from electron acceleration rings, allows in situ investigations of the damage evolution process during tensile loading in composite materials. In this context, the development of adequate scientific instrumentation as well as the understanding of the corresponding technology by research groups is paramount to guarantee reliability of the obtained results. In the present work, a miniaturized universal testing machine (tensile, compression and fatigue) was developed to be applied in in situ µCT experiments using synchrotron radiation with innovative technology. The equipment has a uniaxial load capacity of up to 300 N with 1 N resolution and can impose 0.01 mm resolution displacements following controlled deformation rates. In order to validate the developed equipment, tensile test results performed on sub-sized and standard annealed copper specimens were compared and in situ µCT tensile tests were performed in glass-fiber-reinforced polypropylene matrix composites at the Laboratorio Nacional de Luz Sincrotron (LNLS) in Campinas (SP, Brazil). Data analysis was performed by applying image processing techniques to successive tomograms in order to monitor crack propagation in the initial stages of damage evolution. The results obtained allowed the clarification of crack propagation mechanisms in the investigated composite materials and demonstrated the viability of the equipment’s intended application.

Mathematical Modeling of Failure Process of AlMg2.5 Alloy in High and Very High Cycle Fatigue

Prediction of the endurance limit in the high and very high cycle loading range (102−1010) is an important problem in aircraft engine construction and high-speed rail transport. It involves the development of models and their experimental verification taking into account damage evolution stages and fatigue crack growth in a damaged medium. A damage evolution model that takes into account the kinetics of defects and microplasticity effects was proposed. The model was used to study the process of fatigue failure of an AlMg2.5 structural alloy. The model parameters were identified and verified using experimental data on static, dynamic, and fatigue loading, as well as tests at various temperatures. The numerical results were used to construct the Wohler curve, which was found to agree well with experimental data in the range of high cycle fatigue. The duality effect of the S-N curve was described. A computational experiment was performed to study the effect of dynamic loading on the fatigue strength. It was found that the fatigue limit depends weakly on the preliminary dynamic strain, which was confirmed by experimental data. Various mathematical packages and numerical methods for solving the constructed system of differential equations were compared. The Adams method and its modifications were shown to be optimal for the numerical integration of the problem under consideration. Wolfram Mathematica was found to be a preferred software package for numerical solution. The convergence of the numerical solution was investigated.

The Experimental Prediction of the Lifetime of Acrylonitrile Butadiene Styrene (ABS) by the Energetic Method

In this paper, we are dealing with the study of the mechanical behavior of an amorphous polymer, acrylonitrile butadiene styrene "ABS". In fact, uniaxial tensile tests on rectangular specimens containing a combined defect, with simple and double notches, has been done. The proposed approach develop a method, based on energy parameter, to calculate the evolution of damage over the materials’ life. This method can be used to predict quantitatively the risk of sudden rupture in a structure. Therefore, the damage evaluation based on the residual energy method was compared to the unified theory one for different loading levels. The prediction of damage by experimental models has led to the determination of the three stages of damage evolution, which are the initiation, propagation and complete deterioration of the material. Thus, the concept of reliability is used to specify the critical life fraction, which is similar to the notch depth (βc) of a modeled defect as a combined defect on an ABS sample. In addition, the unified theory was used in this work, to define on the one hand, the parameter of damage which is the internal variable which describes the failure level of the structure in function of life fraction, on the other hand, for the theoretical evaluation of the level of damage. Finally, we have proved that the theoretical and experimental results show a good agreement.

Prediction of thermomechanical behavior of acrylonitrile butadiene styrene using a newly developed nonlinear damage-reliability model

The aim of this work was to evaluate the influence of temperature on the mechanical behavior of an amorphous polymer, namely acrylonitrile butadiene styrene (ABS), based on a series of uniaxial tensile tests on smooth specimens at different temperatures. The results demonstrate that the behavior of the polymers is strongly dependent on the temperature. Its influence on the physical characteristics during the study of polymer behaviors cannot be denied, particularly when the processes of shaping are investigated, which require significant contributions of heat and mechanical effort. For this reason, this study consists of predicting the evolution of ABS damage in two main zones. The first is the industrial zone, in which the configuration of macromolecular chains is largely immobile, and the temperature is below the glass temperature (Tg = 110°C). In this zone, a damage model based on the obtained experimental results allowed us to determine three stages of damage evolution, and then to specify the critical fraction of life, at which the material becomes unstable and defective, for the purpose of predictive maintenance. The second zone is that of thermoforming, in which the temperature is above the glass temperature, Tg. In this zone, the macromolecular chains tend to move more freely as the temperature increases. The same damage model was adopted to follow the flow process according to the fraction of life that represents the critical material parameter. This study also includes a comparison between the static (experimental) damage models and unified theory (theoretical) damage models.

Study on Multiparameter Precursory Information Identification of the Fracture of Yellow Sandstone

In order to explore the disaster caused by uncontrollable instability of coal and rock mass, a multiparameter fusion system is constructed to predict and predict disasters more accurately by identifying the mechanical and acoustic precursors of coal and rock fracture. In order to explore the precursor information of yellow sandstone rupture, the damage evolution process of yellow sandstone is analyzed from the four aspects of rock mechanics, acoustic emission time domain, frequency domain, and characteristic parameters, and the body strain, dissipated energy and acoustic emission counting, acoustic emission energy, average frequency, peak frequency, b value, and entropy value precursor information identification points are obtained, and 8 parameters are analyzed by time series fusion. The specific conclusions are as follows: body strain in the violent stage of damage evolution, the slope is zero, the zero end point is the precursor information identification point, the dissipative energy curve overall shows the “s” type, the early growth rate is faster—the medium‐term stability—the later period is slowed down, and the upper slope boundary point of the “s” type curve is used as the precursor information identification point. In the violent stage of damage evolution, the layered features of the acoustic emission count are obvious, the specific gravity shift is more obvious, and the high count appears as the precursor information identification point; the acoustic emission energy accumulates the high‐energy signal and is accompanied by the steady and rapid growth of energy as the precursor information identification point. The effects of shearing main cracks, shear microcracks, tensile cracks, and composite cracks on the acoustic emission count and energy in the damage evolution process are analyzed. The increase of medium‐ and high‐frequency signals and the reduction of high‐frequency signals predict the rupture. The average frequency signal change law is continuous high frequency‐blank‐continuous high frequency, with the blank period end point as the damage precursor identification point; the b value damage evolution stage shows a continuously steady increase to a rapid increase, with the continuous stable growth starting point as the crack identification point. In the process of damage evolution, the sample entropy presents an orderly, chaotic, disordered, and orderly process. The end of chaos and the beginning of disorder are used as the prejudging demarcation points. Based on the time sequence, an eight‐parameter comprehensive early warning system is constructed. The indicators are classified into five levels for early warning in the stage of severe damage evolution. The identification of multiparameter precursory information of yellow sandstone provides a new research idea and analysis angle and method for the failure of other coal and rock masses.

Endurance and Damage in Fatigue of Symmetrical Configuration 2P-2V-2P Perlon-Glass-Acrylic Composite Laminates of Orthopaedic Use

In this paper, an experimental characterization of fatigue behaviour on prismatic specimens of a symmetrical laminated composite material perlon- glass- acrylique 2P-2V-2P for orthopaedic use is conducted. Cyclic repeated solicitation is employed corresponding to applied minimum stress σmin equal zero. The various loading levels imposed on the specimens are 80%, 70%, 60%, 55%, 45%, 35% and 25% of the value of the static failure strength measured in flexure. A significant scatter characterizes the results of material fatigue lifetime. That is the consequence of the heterogeneity of the material structure. The scattered phenomenon prevents any prediction of the lifetime with a good probability using Wohler equation. This enables defining a constant degradation rate by 10% cycle decade. The microstructure morphology study through microscopic observations is also discussed and analyzed. The damage state in fatigue is characterized by a combination of density and orientation of micro-cracks. This damage is mainly due to mechanisms complexity of matrix micro-cracking, inter facial exfoliation, debonding and delamination. The damage evolution stages in the case of cyclic loading have the same nature than those found in static loading but have different chronology and scale.

Non-linear ultrasonic monitoring of damage progression in disparate rocks

This paper focusses on non-destructive characterization of stress-induced damage progression in three types of rocks by experimentally capturing the elasto-dynamic non-linear response of the rocks, with the hypothesis that non-linear approaches have increased sensitivity relative to linear ultrasonic testing approaches. For this task, a non-linear ultrasonic testing procedure known as the Scaling Subtraction Method (SSM) has been implemented on uniaxially loaded rock specimens. The SSM procedure is based on exciting the damaged medium with two acoustic signals at different amplitudes consecutively. The linearly rescaled acoustic response at low excitation is subtracted from the response at large amplitude excitation for quantification of the elastic non-linearity of the medium by a non-linear indicator θ. At first, aluminum, Lyons sandstone, granodiorite and Gosford sandstone specimens were characterized using SSM and their inherent non-linearity was quantified. After this, the rock specimens were loaded under uniaxial compressive step-loading and ultrasonic measurements were performed simultaneously at each loading step. The non-linear indicator θ was calculated as the specimens were progressively damaged, and the changes in the non-linear response were linked to the different physical processes accompanying damage progression in rocks. The study concluded that the non-linear SSM technique is capable of sensitively recording signatures of the different stages of damage evolution in rocks.

Determination of ductile damage behaviors of high strain rate compression deformation for Ti-6Al-4V alloy using experimental-numerical combined approach

Ductile damage behavior of Ti-6Al-4V alloy was characterized by the evolution of flow curves and deformed specimens in compression tests at high strain rates and various temperatures. Cracks along the shear bands of deformed specimens were observed at lower temperatures (20 °C and 100 °C) and high strain rates (2500–10,000 s−1). The failure initial strains (FIS) during crack generation were calculated according to the measured flow stresses at the transition from stable plastic to damage evolution stage. Special emphasis is placed on the influence of strain rate and temperature on the ductile failure initiation. The failure initiation parameters of Johnson-Cook (JC) damage model were obtained by genetic algorithm (GA) optimization using a combined experimental–numerical approach. That is, the ductile damage parameters were optimized according to the measured FIS and the simulated stress triaxiality, equivalent strains, stresses and temperatures, using compression simulation without damage model. At lower temperatures (T < 300 °C), the failure parameters were used to simulate the flow stresses and deformation of specimen by the JC plastic and damage models. To further validate the failure parameters, at higher temperatures (T ≥ 300 °C), a coupling modified JC (JCM) plastic and energy density based damage model was proposed to characterize the flow curves at damage evolution stage by compression simulation using a subroutine program. The predicted flow stresses and the deformed specimens were consistent with the experimental results.

A Research on Fatigue Damage Constitutive Equation of Asphalt Mixture

The laboratory investigations of fatigue damage constitutive equation of asphalt mixture were carried out by three-point bending fatigue tests. The three-point bending fatigue tests were performed at three levels of stress-strength ratio (SSR), temperature, and loading rate. The coupled multifactor (stress-strength ratio, temperature, and loading rate) fatigue life equation was established, which can well predict the fatigue life of the asphalt mixture. Both a damage model and a damage evolution equation have been established based on the E-N curve, which indicate that fatigue damage evolution is nonlinear and consists of three stages. The sensitivity analysis of damage model parameters indicates that each parameter has different effects on the three stages of damage evolution. Based on the researches above, the fatigue damage constitutive equations were finally built based on the σ-ε curves, which consist of two parts: the damage accumulation stage and the fatigue failure stage. The elasticity-power hardening model was used to describe the constitutive relation of damage accumulation stage. The elasticity-power hardening model and the Sidoroff damage model were used to describe the constitutive relation of damage failure stage. The constitutive equations can well characterize the fatigue damage performance of the asphalt mixtures under cyclic loading.

Experimental investigation on damage evolution behaviour of a granitic rock under loading and unloading

In-situ rock failures can result from stress changes due to pure loading and/or unloading. Understanding of the damage evolution behavior in brittle rocks during loading and unloading is imperative for the designs of rock structures. In this paper, we investigate the damage evolution characteristics of a granitic rock during loading and unloading after a series of triaxial experiments performed at different confining pressures. The axial stress—axial strain variations of the tested specimens revealed that the specimens undergoing unloading fail with a lower axial strain compared to the specimens failed purely by loading. Higher confining pressures were observed to exacerbate the difference. Volumetric strain versus axial strain curves indicated that the curves reverse the trend with the beginning of major damage of specimens. We suggest here a new form of equation to describe the secant modulus variation of brittle rocks against the axial stress for the unloading process. Failure mechanisms of tested specimens showed two distinct patterns, namely, specimens under pure loading failed with a single distinct shear fracture while for the unloading case specimens displayed multiple intersecting fractures. In addition, analysis of the evolution of dissipation and elastic energy during deformation of the specimens under loading and unloading conditions showed differentiable characteristics. Moreover, we evaluated the variations of two damage indices defined based on the energy dissipation and secant modulus evolution during deformation and observed that both of them satisfactorily distinguish key stages of damage evolution.

Effect of pore structure on fatigue of pervious concrete

Pervious concrete (PC) is a class of porous pavement whose properties are largely influenced by pore parameters. Under repeated vehicular loads, PC undergoes reduction in stiffness leading to failure. The purpose of this study was to understand the influence of porosity and pore sizes on fatigue of 13 PC mixtures encompassing 104 beams, and establish stiffness reduction model / damage evolution in respect of repeated loads for PC based on the existing model used for conventional concrete. Fatigue life and stiffness depend on porosity at the fractured face of specimens as investigated using image analyses, which was more influential than the volumetric porosity determined through ASTM C1754. The reduction in stiffness followed S-curve depicting three distinct stages of damage evolution. The damage model fitted the experimental data with very high accuracy (R2 > 0.95) and precision. The specimens shifted from secondary to tertiary stage when the reduction in initial stiffness was 65–85%, which occurred at 90–98% of the total life. This study is envisioned to assist in the development of fatigue test protocols as well as recommend PC pavements as part of the maintenance and rehabilitation programmes.

Research on the dynamic mechanical properties of C-plane sapphire under impact loading

Sapphire is widely used as optical materials and substrate materials because of its excellent physical and chemical properties. The dynamic mechanical properties under impact loading are very important for the sapphire parts used in extreme conditions. In this study, the dynamic mechanical properties of C-plane sapphire have been tested on the Split Hopkinson Pressure Bar. The true stress-strain curve of sapphire has been obtained at different velocities. The failure process of sapphire has been observed via high-speed photography. And the fracture morphology of sapphire after impact was analyzed. It is found that sapphire undergoes a very small linear section under impact loading. Subsequently the microcrack damage evolution stage occurs and then crack propagation is instability after reaching the compressive limit. It is found that the impact velocity has no effect on the linear elastic section of sapphire, but the compressive strength and fracture of sapphire will increase with increasing impact velocity. The crystal orientation influences the crack path and crack pattern, which lead to different energy consumption during crack propagation.

CT Experimental Study on the Damage Characteristics of Anchored Layered Rocks

A laboratory physical simulation and a CT scan test were conducted to analyze the anchoring mechanism of a system anchor bolt and a steel floral pipe in a layered rock mass. The following conclusions were drawn: (1) The anchoring effect of the system anchor bolt and steel floral pipe improves the strength parameter of the layered rock, and the system anchor bolt provides higher improvement. Neglecting the jointing effect, the improvement in the strength parameter of the layered rock due to the anchor bolt is primarily reflected by the following three aspects: the compressive zone effect of the preload, the repairing effect of the anchoring agent on defects in country rocks, and the reinforcement effect of the anchor bolt on the overall strength and density of the anchoring object. Considering the jointing effect, the improvement in the strength parameter of the layered rock due to the anchor bolt is reflected by improvement in the deformability and shear strength of the joint surface. (2) The stress-strain curves of the anchored specimens can be divided into different stages of damage evolution, based on the angles of bedding. (3) The crack-arresting effect of the anchor bolt is due to the weakening, cutting, and arresting of the cracks in the anchorage zone. The larger the anchorage zone, the better is the crack-arresting effect.

The fatigue failure study of repaired aluminum plates by composite patches using Acoustic Emission

The aim of this study is to investigate the failure of cracked aluminum plates repaired by one-side composite patches under fatigue loading using Acoustic Emission (AE) and fractography images. Rectangular specimens made of 6061 aluminum alloy with central through thickness pre-cracks were repaired using glass/epoxy laminated patches. The specimens were subjected to the fatigue loading and AE technique was employed to monitor the effect of the repair patch on the damage progression. First, different stages of damage evolution were studied based on the mechanical data and fractography images. Then, the AE energy utilized to characterize failure process of the specimens. To this aim, AE signals of the aluminum cracking and adhesive layer failure were discriminated according to their energy content. The effect of patch thickness and layup on the failure behavior of the specimens were also studied. Finally, it is concluded that AE is a powerful technique to characterize the failure process of a repaired cracked aeronautic structure by composite patches.

Deterministic modeling of API5L X52 steel in a coal-tar-coating/cathodic-protection system in soil

Impedance characteristic signal for a coal tar-coated API5L-X52 steel with cathodic protection has been investigated in soil using electrochemical impedance spectroscopy (EIS). Deterministic transmission line model (TLM) has been set up to simulate the impedance results of pipeline with intact and artificial defect coating, and to verify the damage evolution of coated pipeline with cathodic protection in soil. To illustrate the coating inherent property, coating in each transmission line unit has been assumed to be represent by two imaginary parts: a relatively coating barrier part which serves as parallel of capacitor and resistor (Cper Rper); and another part considered as porous coating serves as parallel of porous coating and double layer (Cpor Rpor (Cdl Rct)). The parameter θ has been proposed to calculate the total impedance of the coating, to illustrate its performance. An adjustment was applied to calculate total resistance Rt mathematically, based on the simulation results to illustrate the damage evolution concept. The Rt values are in agreement with the proposed damage evolution stages.

Multiscale characterisation of the mechanical properties of austenitic stainless steel joints

A multiscale investigation was pursued in order to obtain the strain distribution and evolution during tensile testing both at the macro- and micro-scale for a diffusion bonded 316L stainless steel. The samples were designed for the purpose to demonstrate that the bond line properties were equal or better than the parent material in a sample geometry that was extracted from a larger component. The macroscopic stress-strain curves were coupled to the strain distributions using a camera-based 2D – Digital Image Correlation system. Results showed significant amount of plastic deformation predominantly concentrated in shear bands which were extended over a large region, crossing through the joint area. Yet it was not possible to be certain whether the joint has shown significant plastic deformation. In order to obtain the joints’ mechanical response in more detail, in situ micromechanical testing was conducted in the SEM chamber that allowed areas of 1x1mm2 and 50x50mm2 to be investigated.The size of the welded region was rather small to be accurately captured from the camera based DIC system. Therefore a microscale investigation was pursued where the samples were tested within an SEM chamber. Low magnification SEM imaging was utilised in order to cover a viewing area of 1mm×1mm while high magnification SEM imaging was employed to provide evidence of the occurrence of plastic deformation within the joint, at an area of just 50μm×50μm. The strain evolution over the microstructural level, within the joint and at the base material was obtained. The local strains were highly non-homogeneous through the whole test. Final failure occurred approximately 0.2mm away from the joint. Large local strains were measured within the joint region, while SEM imaging showed that plastic deformation occurs via the formation of strong slip bands, followed by the activation of additional slip systems upon further plastic deformation which end up in additional slip bands to form on the surface. Plastic deformation occurred by slip and twinning mechanisms. Upon necking, significant out of plane deformations and slip deformation mechanisms were observed which suggested that plastic deformation was also happening at the last stages of damage evolution for the specific alloy. This was also evident from the large difference between the 600MPa UTS stress value and the low stress values before final failure (which in many cases was below 30MPa).

Early stage damage in off-axis plies under fatigue loading

The very early stages of damage evolution under fatigue loadings were investigated by testing [45/-45/0]s glass/epoxy specimens. Microscope observations revealed that the first damage event was the initiation of micro-cracks in the 45° plies within the inter-fibre region. Off-axis cracks then formed by the coalescence of these micro-cracks and propagated along the fibres direction with the same mechanism. The orientation of the micro-cracks was proven to be normal to the direction of the local maximum principal stress in the matrix. The results presented here are the first published evidences of fatigue damage initiation at the inter-fiber scale and represent a further validation of the fatigue crack initiation criterion recently presented by the authors.