Degradation Of Material Properties Research Articles

Numerical modelling of cancellous bone damage using an orthotropic failure criterion and tissue elastic properties as a function of the mineral content and microporosity

Background and objective: Elastic and strength properties of lamellar tissue are essential to analyze the mechanical behaviour of bone at the meso- or macro-scale. Although many efforts have been made to model the architecture of cancellous bone, in general, isotropic elastic constants are assumed for tissue modelling, neglecting its non-isotropic behaviour. Therefore, isotropic damage laws are often used to estimate the bone failure. The main goals of this work are: (1) to present a new model for the estimation of the elastic properties of lamellar tissue which includes the bone mineral density (BMD) and the microporosity, (2) to address the numerical modelling of cancellous bone damage using an orthotropic failure criterion and a discrete damage mechanics analysis, including the novel approach for the tissue elastic properties aforementioned.Methods: Numerical homogenization has been used to estimate the elastic properties of lamellar bone considering BMD and microporosity. Microcomputed Tomography (μ-CT) scans have been performed to obtain the micro-finite element (μ-FE) model of cancellous bone from a vertebra of swine. In this model, lamellar tissue is orientated by considering a unidirectional layer pattern being the mineralized collagen fibrils aligned with the most representative geometrical feature of the trabeculae network. We have considered the Hashin’s failure criterion and the Material Property Degradation (MPDG) method for simulating the onset and evolution of bone damage.Results: The terms of the stiffness matrix for lamellar tissue are derived as functions of the BMD and microporosity at tissue scale. Results obtained for the apparent yield strain values agree with experimental values found in the literature. The influence of the damage parameters on the bone mechanics behaviour is also presented.Conclusions: Stiffness matrix of lamellar tissue depends on both BMD and microporosity. The new approach presented in this work enables to analyze the influence of the BMD and porosity on the mechanical response of bone. Lamellar tissue orientation has to be considered in the mechanical analysis of the cancellous bone. An orthotropic failure criterion can be used to analyze the bone failure onset instead of isotropic criteria. The elastic property degradation method is an efficient procedure to analyze the failure propagation in a 3D numerical model.

Evolution of Anand Parameters for Thermally Aged Sn-Ag-Cu Lead-Free Alloys at Low Operating Temperature

Abstract In extreme environmental applications, such as aerospace and automotive, electronics may endure high or low operating temperatures during service, handling, and storage. An electronic assembly may experience strain rates of 1–100 per sec of strain and ambient temperatures of –65 to +200 °C. Electronic assembly's temperature depends mainly on location, energy dissipation, and thermal architecture. Electronic assemblies in automotive applications may be located underhood, on engine, on-transmission, and or in wheel well. Study of property evolution of solders used for interconnection is important for assurance of reliability. Degradation in material properties for lead-free solder alloys can be caused by change in microstructure due to variation in temperatures. There is need for data on the effect of operating period and operating conditions on the material properties. Addition of dopants in Sn-Ag-Cu (SAC) alloys has been shown to improve mechanical properties and minimize deterioration due to aging at lower strain rates. SAC-Q is formulated with Sn-Ag-Cu with addition of Bi (SAC+Bi). It has been observed that adding Bismuth (Bi) to SAC alloy can play an important role to make the solder alloy resistant to aging-induced degradations. In author's prior research the evolution of Anand parameters and materials properties for SAC solder (SAC105, SAC305, and SAC-Q) at high temperatures and high strain rates has been studied. However, data on thermally aged SAC solder alloys at high strain rate levels at low operating temperatures are not available in published literature. In this paper, materials characterization of thermally aged SAC (SAC105 and SAC-Q) solder at low operating temperatures (−65 °C to 0 °C) and at high strain rates (10–75 per sec) has been studied. Stress–strain curves have been measured at low operating temperatures using impact hammer-based tensile tests with cooling chamber. The fabricated SAC lead-free solder specimen was isothermally aged up to 6 months at 50 °C before testing. Anand viscoplastic model has been used to compute nine Anand parameters to describe the material constitutive behavior. Anand Model parameters evolution due to thermal aging has been studied for SAC solders. The computed nine Anand parameters from experimental data then were used to simulate the tensile test to predict the stress–strain curve and compared to experimental stress–strain curves to verify the accuracy of the model. A good correlation was found between experimental data and Anand-predicted data.

Stress state failure analysis of thin-walled GLARE composite members subjected to axial loading in the post-buckling range

The paper investigated the load-carrying capacity and the participation of stress components in the failure analysis of top-hat-shaped composite columns subjected to uniform compression. GLARE members were axially compressed in laboratory tests employing a static testing unit. Failure tests were monitored in the full load range using the digital image correlation (DIC) system, which enabled visualization of full-field displacements and strains. Simultaneously, FEM numerical simulations were carried out to estimate the load-carrying capacity of the top-hat-shaped sections based on the nominal stress state in both the non-degraded and degraded composite models. In the latter, the material property degradation method (MPDG) allowed a progressive lowering of the material stiffness based on the presumed damage variables. Failure initiation in composite plies was monitored in FE simulations based on Hashin and Puck failure criteria. Stress state analysis was performed to investigate the participation of stress tensor components in the failure function of selected failure criteria. This enabled the identification of critical stresses contributing to aluminum plastic deformation and intra-laminar failure mechanisms that led to the composite fracture. The results of the numerical simulations were found to be in high agreement with the experimental evidence.

Radiation effect studies on partially crystalline bulk amorphous Fe-based metallic glass

The selection of appropriate materials for radiation environments is critical due to the harsh and aggressive conditions found in such environments, which are liable to degrade material properties. Therefore, durability of materials should be tested before being deployed. In this respect, proton tests are required for the materials to be used in the space environment because dominant galactic cosmic rays mostly comprised high energy protons. Bulk metallic glasses are candidate for space environment due to their desirable properties such as high strength, high corrosion resistance, and lack of grain boundaries. In this present study, we report the effect of a 30 MeV proton beam irradiation on the structural, thermal, mechanical, and magnetic properties of partially crystalline bulk amorphous Fe-based metallic glass. Defect size increment in positron annihilation lifetime spectroscopy and small intensity changes on the X-ray diffraction peaks of samples were observed after the irradiation that can be attributed to increasing free volumes. In addition, changes in crystallisation and glass transition temperatures were examined in differential scanning calorimetry. Furthermore, rise in coercivity which is a magnetic property was observed in vibrating sample magnetometer that may associate with the defect size increment. On the other hand, any changes were not observed on the microhardness measurements.

Nonlinear finite element modeling of the impact of reinforcement corrosion on bridge piers under concentric loads

AbstractCorrosion of reinforcing steel in reinforced concrete (RC) infrastructure is one of the most detrimental deterioration mechanisms, affecting both safety and serviceability. In the present study, a comprehensive analysis methodology of corrosion damage is adopted. The detrimental effects of corrosion‐induced degradation of material properties on the ultimate capacity of an existing aging RC bridge pier under concentric loading are investigated. A three‐dimensional nonlinear finite element analysis using the commercially available finite element program DIANA is used. The main corrosion‐induced deteriorating factors considered in the present study are: concrete strength degradation within the cover and part of the confined concrete core due to corrosion‐induced cracking, degradation of confinement effects, steel area reduction due to uniform corrosion (in both longitudinal and tie reinforcement), steel ductility degradation due to pitting corrosion, buckling of compressive steel bars due to cross‐section reduction and confinement degradation, and bond strength degradation between steel and concrete induced by concrete cracking/spalling. The methodology is evaluated by comparing the numerical results to those of corroded column tests reported in the literature.

Asynchronous Synergistic Damage Effect of Atomic Oxygen and Space Micro Debris on Kapton Film

In the low earth orbit environment, many environmental factors lead to the degradation of material properties. The synergistic effect of long-term atomic oxygen (AO) irradiation and instantaneous impact of micro debris (MD) on long-term and transient space environmental factors has attracted more and more attention. In this paper, the performance evolution of Kapton films under the conditions of MD, AO single factor load spectrum and MD + AO, AO + MD asynchronous synergistic load spectrum were studied by laser driven flyer and microwave atomic oxygen technology. The macro morphology, optical properties and quality changes of Kapton films before and after each load spectrum were compared, and the mechanism of micro morphology and structure changes was explored. The results show that compared with MD + AO loading spectrum, the surface holes of Kapton films are larger under AO + MD load spectrum condition, the residual aluminum particles formed by reverse sputtering of Al particles during impact are less, the average transmittance of the film decreases slightly, and the weight loss of Kapton film is slightly more under the same atomic oxygen exposure time. Under the condition of MD + AO load spectrum, plastic tearing cracks, craters and holes are formed on the surface of Kapton film; the edge of the hole formed under the condition of AO + MD load spectrum is straight, without obvious depression and tear characteristics. Under the condition of MD + AO load spectrum, due to the adhesion of Al after the impact of micro debris, the subsequent atomic oxygen erosion of the film is reduced, so the C-C bond is not seriously damaged, and a considerable part of the residual aluminum flyer is oxidized to alumina by atomic oxygen; The AO + MD loading spectrum test makes the film first eroded by atomic oxygen, resulting in the reduction in C–O bond and C–C bond. The fracture of C–N bond is caused by the hypervelocity impact of micro debris. Hypervelocity impact leads to the thermal decomposition of the material, destroys the C–N bond in the imide ring and generates an N–H bond. This study will provide a method reference and a reference for the multi-factor ground collaborative simulation of space environment of spacecraft materials.

Finite element method based micromechanical methodology for homogenizing fiber/fabrics-reinforced composites and their progressive failure

The complex microstructure of fabrics makes it challenging to homogenize them using an analytical/semi-analytical micro-mechanics approach like the Mori-Tanaka and the method of cells. Analytical approaches developed for fabrics estimate their elastic constants and do not easily accommodate material nonlinearities. Numerical schemes such as the finite element method (FEM) have been developed to analyze failure in fabrics and not necessarily find moduli of the homogenized material. Here we use the FEM based micro-mechanics approach to both homogenize fiber-reinforced and plain/twill/satin weave, as well as braids/fabrics-reinforced composites using simplified unit cells. The homogenization is based on Hill’s averaging theorem and employs tie constraints to impose periodic displacements and anti-periodic tractions on boundaries of the unit cell. A continuum damage mechanics approach is used to study damage initiation and progression, and degradation of material properties. The predicted elastic constants, failure modes and ultimate strengths of fabrics are found to compare well with their either experimental or computed values available in the literature. We have also analyzed delamination and damage propagation in a laminate with an open hole at the centroid and uniform tensile tractions at its end faces to estimate its ultimate strength that is found to agree well with the experimental value.

Conducting Poly[N-(4-Methoxy Phenyl)Maleamic Acid]/Metals Oxides Nanocomposites for Corrosion Protection and Bioactivity Applications

Corrosion is considered as the most common cause of steel material property degradation, while coatings are effective and popular corrosion protection methods. Coatings come in a variety of forms, each with its own set of effectiveness, methods and constituents. This study used an electrochemical oxidation approach to make Poly [N-(4-Methoxy Phenyl) maleamic acid] from monomer [N-(4-Methoxy Phenyl) maleamic acid] (NPM) in a 3.5% seawater solution. On a low carbon steel [L.C.S] electrode (working electrode), a polymer film was produced. The polymer was created, according to infrared, SEM and FTIR examinations. Using the electrochemical polarization approach, the anticorrosion function of polymer films on L.C.S was examined. Also, adding nanoparticles (NP), like CuO and ZnO to the monomer solution improved the polymers anticorrosion. The results revealed that there was an increase in the L.C.S corrosion rate with the increase of temperature from 293K to 323K, while the values related to coatings polymer inhibition efficiency improved with NPs addition. For the corrosion of L.C.S in salt medium prior to and following polymeric coating, thermodynamic and kinetic activation parameters were estimated. The impact of preparing polymers on certain bacteria strains was also investigated.

A material property degradation model of composite laminates considering stress level

Conventional phenomenological models of composite laminates often require a large amount of experimental data due to the dependence on stress level. In this study, a new generalized model capable of predicting the material property degradation at each stress level using a single set of parameters is proposed to dramatically subside the experimental cost. Furthermore, two sets of residual strength data and one set of residual stiffness data are adopted to validate the proposed model. The results show that the new model is capable of predicting both residual strength and stiffness at arbitrary stress levels using single set of model parameters.

Understanding the Radiation Resistance Mechanisms of Nanocrystalline Metals from Atomistic Simulation

Metallic materials produce various structural defects in the radiation environment, resulting in serious degradation of material properties. An important way to improve the radiation-resistant ability of materials is to give the microstructure of materials a self-healing ability, to eliminate the structural defects. The research and development of new radiation-resistant materials with excellent self-healing ability, based on defects control, is one of the hot topics in materials science. Compared with conventional coarse-grained materials, nanocrystalline metals with a high density of grain boundary (GB) show a higher ability to resist radiation damage. However, the mechanism of GB’s absorption of structural defects under radiation is still unclear, and how to take advantage of the GB properties to improve the radiation resistance of metallic materials remains to be further investigated. In recent decades, atomistic simulation has been widely used to study the radiation responses of different metals and their underlying mechanisms. This paper briefly reviews the progress in studying radiation resistance mechanisms of nanocrystalline metals by employing computational simulation at the atomic scale.

Creep–Fatigue Interaction Effects on Pressure-Reducing Valve Under Cyclic Thermomechanical Loadings Using Direct Cyclic Method

Abstract Supercritical boiler system has been widely used to increase efficiency of electricity generation in power plant industries. However, the supercritical operating condition can seriously affect structural integrity of power plant components due to high temperature that causes degradation of material properties. Pressure reducing valve is an important component being employed within a main steam line of the supercritical boiler, which occasionally thermal-fatigue failure being reported. This research has investigated creep-cyclic plastic behavior of the pressure reducing valve under combined thermomechanical loading using a direct numerical method known as extended direct steady cycle analysis of the linear matching method framework (LMM eDSCA). Finite element model of the pressure-reducing valve is created based on a practical valve dimension and temperature-dependent material properties are applied for the numerical analysis. The simulation results demonstrate a critical loading component that attributes creep-fatigue failure of the valve. Parametric studies confirm the effects of magnitude of the critical loading component on creep deformation and total deformation per loading cycle. With these comprehensive numerical results, this research provides engineer with an insight into possible failure mechanisms of the pressure-reducing valve at high temperature.

Fatigue life prediction model and entropy generation of 304L stainless steel fabricated by selective laser melting

Fatigue performance and reliability application have always been the key issues restricting the development of disruptive additive manufacturing technology due to intrinsic defects caused by the manufacturing process. In the present work, tensile tests and fatigue tests of 304 L stainless steel (SS) fabricated by selective laser melting (SLM) with various laser power levels were carried out with in-situ monitoring of acoustic emission (AE) and thermal imager (TI). Microstructural characterizations were performed to measure the surface roughness, porosity, and residual stress of as-built SLMed 304 L SS. A fatigue life prediction model considering surface roughness, porosity, and residual stress was established based on experimental data. In addition, direct evidence is offered to show the strong correspondence between the temperature variable of material surface induced by energy dissipation caused by entropy generation during cyclic deformation and the degradation of material properties caused by fatigue micro-damage. This work indeed provides a novel fatigue life prediction model for SLMed 304 L SS, and advances our current understanding of underlying fatigue micro-damage mechanism of additively manufactured materials.

Numerical study on butterfly wings around inclusion based on damage evolution and semi-analytical method

Butterfly wings are closely related to the premature failure of rolling element bearings. In this study, butterfly formation is investigated using the developed semi-analytical three-dimensional (3D) contact model incorporating inclusion and material property degradation. The 3D elastic field introduced by inhomogeneous inclusion is solved by using numerical approaches, which include the equivalent inclusion method (EIM) and the conjugate gradient method (CGM). The accumulation of fatigue damage surrounding inclusions is described using continuum damage mechanics. The coupling between the development of the damaged zone and the stress field is considered. The effects of the inclusion properties on the contact status and butterfly formation are discussed in detail. The model provides a potential method for quantifying material defects and fatigue behavior in terms of the deterioration of material properties.

On the effect of pit shape on pitted plates, Part I: Tensile behavior due to artificial corrosion pits

Pitting corrosion threatens the safety of steel structures by degrading material properties. In this paper, the effect of pitting damage on tensile behavior of Q345 and Q235 steels is studied experimentally and numerically. Material tensile tests were carried out on small steel specimens with artificially introduced corrosion pits of a cylindrical, semi-ellipsoidal, or conical shape, and used to validate their numerical models. Numerous numerical analyses were carried out to study the tensile properties and behavior of different steels due to varying pitting features in the pit shape and degree of volume loss (DOV) of corroded material. Results showed that pit shape influences the tensile properties of corroded steel significantly, depending on the ratio of pit diameter to pit depth. In the worst case, variation of pit shape could result in a difference of 7.58% in strength deterioration, and it could become worse if combined with the random nature of pit size, pit depth, and pitting distribution. An equivalent material model was proposed to correlate the reduction ratios of tensile properties with the DOV and pit shape. The ultimate strength of pitted plates can be predicted properly, using the equivalent material model instead of modelling the detailed corrosion pits.

Preliminary Analysis of an Aged RPV Subjected to Station Blackout

Today, 46% of operating Nuclear Power Plants (NPP) have a lifetime between 31 and 40 years, while 19% have been in operation for more than 40 years. Long Term Operation (LTO) is an urgent requirement for all of the nuclear industry. The aim of this study is to assess the performance of a reactor pressure vessel (RPV) subjected to a station blackout (SBO) event. Alterations suffered by the material properties and creep at elevated temperatures are considered. In this study, coupling between MELCOR and Finite Element Method (FEM) codes is carried out. In the Finite Element (FE) model, the combined effects of ageing and creep are implemented through degraded material properties and a viscoplastic model. The reliability of the model is validated by comparing the FOREVER/C1 experimental results. The results show that the RPV lower head bends downwards with a maximum radial expansion of about 260 mm and RPV thermomechanical properties are reduced by more than 50% at high temperatures. The effects of ageing, creep and long heat-up strongly affect the resistance of the RPV system until the point of compromising it in the absence of/delayed emergency intervention. Aged RPV at end-of-life may collapse earlier, and in less time, with the same accidental conditions.

Алгоритм расчета накопления повреждений на примере узла крепления вертолетной лопасти

In this research we develop an algorithm for calculating damage accumulation for metal-composite joints using the example of a helicopter blade attachment. The degradation of the composite material properties is investigated, since operation of composites leads to decline in their main mechanical properties, namely, stiffness and toughness as a result of possible binder failure. Damage growth in fibre-reinforced composites is a very complex process due to their heterogeneity and anisotropy. Joints are one of the most vulnerable spots in an aircraft, so joint design should be a priority. Joints can fail for various reasons, for example, assembly stresses, stress concentrations, and technological deviations, which affect the strength of bolted joints. The paper uses computational methods described in the interdisciplinary theory of elasticity, structural mechanics, structural strength, materials science, and mechanics of structural failure of composite materials. This study is aimed at determining the optimal joint assembly to ensure the safe operation of the structure during a specified service life.

Predicting the Nonlinear Damage Response of Imperfect Laminates Using Linear Material Degradation Model and a Semi-Analytical Technique

This paper investigates nonlinear damage response and ultimate collapse of laminates under in-plane and lateral pressure loadings. The in-plane loading was in the form of end-shortening strain, while the lateral pressure was sinusoidal. The plates had initial geometric imperfection to which simply-supported boundary conditions were applied. Ritz techniques with nonlinear strain terms in kinematic relations as well as the first-order shear deformation theory were applied. Hashin and Rotem failure criteria were used for failure analysis. Two models were also employed for degradation of material properties in the plates. The complete ply degradation model was implemented along with the ply region degradation model, in which stiffness reduction was applied only to one region of the ply in which failure had occurred. Note that the stiffness degradation after the failure was investigated as both instantaneous and linear models. In both complete ply and region ply degradation models with instantaneous degradation of material properties, at any location in a ply or region, which has exceeded the given stress criterion, the corresponding stiffness properties are instantaneously degraded throughout that ply or region but with linear material degradation model, the stiffness diminishes gradually and linearly. Finally, the results were then validated against the findings of different references as well as finite element analysis. According to the results, it was seen that in the ply region degradation model, last ply failure loads are generally larger than those of the complete ply degradation model.

Structural behaviour of CFRP strengthened beam-column connections under monotonic and cyclic loading

Welded beam-column connections may be vulnerable to failure under cyclic loading conditions. These connections might require strengthening to resist static and cyclic loads as they may exhibit inadequate capacity due to the design errors or material properties degradation because of severe environmental effects or an increase in service loads. With this in mind, a series of full-scale experiments have been conducted to investigate the behaviour of the bare and strengthened welded beam-column connections under both monotonic and large-displacement cyclic loading. Carbon fibre reinforced polymer (CFRP) is used as the strengthening material in the present study along with epoxy adhesive as the bonding material. The experimental study conclusively showed the benefits of CFRP composites to improve the performance of welded connections under both monotonic and cyclic loadings. Under monotonic loading, the ultimate moment capacity, stiffness, dissipation of energy and ductility of the welded connections improved by strengthening with CFRP. Additionally, under cyclic loading, the CFRP strengthened welded connections showed improvement in moment hysteresis behaviour, higher stiffness and energy dissipation capacity compared to their bare counterparts. Moreover, the experimentally obtained moment capacities match reasonably well with the theoretically predicted moment capacities.

A computational framework for energy absorption and damage assessment of laminated composites under ballistic impact and new insights into target parameters

In this research, by means of advanced methods within the framework of the FE method, an effective modeling approach is proposed to simulate the ballistic perforation behaviors of multi-directional woven composite panels. Within that scope, constitutive models for intraply and interfacial or interply damage mechanisms are formulated and implemented into ABAQUS/Explicit FE code. The constitutive law of ply-level damage model incorporates the nonlinear material response, degradation of material properties, progressive failure and the element deletion scheme. The interfaces between the individual plies are modeled using a cohesive surface method, and the behaviors of interply degradation and failure are described using a traction-separation law. Besides, the material responses with large nonlinearity due to fiber rupture, matrix cracking, plasticity effects due to micro-matrix cracking under shear loading, and interface delamination are accounted for by appropriate material degradation models. The proposed developments are first validated against the available experimental and analytical results. Next, the ballistic impact simulations of woven composite targets are carried out in a two-phase research. The first phase analyzes the ballistic impact behavior and ballistic performance of the composite laminates in terms of residual velocity and energy absorbing capacity. The second phase involves the investigation of the impact characteristics and failure mechanisms of the composite materials. More specifically, the key perforation mechanisms and associated impact damage extents and patterns with respect to projectile velocity are investigated for the composite panels. We further perform parametric analysis in order to understand the influence of a certain number of parameters on the laminate ballistic impact response. These parameters are categorized based on materials such as fiber type material, interface systems, and geometry such as stacking sequences and support conditions. Numerical results reveal that the ballistic impact performance depends significantly on the cohesive material properties, the stacking sequence, and the woven fabric material, whereas less contribution of support conditions to the ballistic perforation characteristic is noticed.

Corrosion Effects on High‐cycle Fatigue Lifetime and Fracture Behavior for Heat‐treated Aluminum‐matrix Nano‐clay‐composite Compared to Piston Aluminum Alloy

In this research, the corrosion effect has been investigated on the high-cycle fatigue lifetime and the fracture behavior for the heat-treated aluminum-matrix nano-clay-composite and piston aluminum alloys. For this objective, after fabricating stir-casted nano-clay-composite, standard samples were machined and rotary bending fatigue tests were performed. To study the corrosion effect, some specimens were corroded in the 0.00235 % H2SO4 solution after 200 h and then, they were tested under cyclic bending loading. Due to increase in the hardness by adding nano-clay particles and the heat treatment, higher fatigue strength occurred, compared to the base material. Moreover, nano-clay particles shortened the fatigue lifetime; however, this effect was less in the corrosion-fatigue lifetime. In addition, the failure mechanism was the brittle fracture behavior due to the observation of quasi-cleavage and cleavage marks. Experimental data illustrated that the H2SO4 environment effect was effectively significant on the bending fatigue lifetime of the piston aluminum alloy, due to corrosion pits and surface defects. This degradation in material properties was demonstrated as a decreasing shift in both low-cycle and high-cycle fatigue regimes.