Damage Evolution Curves Research Articles

Research on uniaxial compression constitutive model of polypropylene fiber recycled brick concrete

Using single factor experiment, different fiber content of the polypropylene fiber recycled brick concrete uniaxial stress-strain curve are studied, then the polypropylene fiber recycled brick concrete damage constitutive model is given and the damage evolution curve is analyzedbased on the Weibull distribution theory and the principle of equivalent strain assumption. Experimental results and analysis show that the addition of fiber not only changes the brittle failure of recycled concrete, but also increases the plastic deformation capacity of recycled concrete: the theoretical curve and test comparing the measured curve fit well; The fiber can effectively inhibit the development of the cracks, improve the deformation capacity and toughness of concrete in a certain range, which is obtained through the damage evolution process of different fiber content.

Autogenous healing on the recovery of mechanical performance of High Performance Fibre Reinforced Cementitious Composites (HPFRCCs): Part 2 – Correlation between healing of mechanical performance and crack sealing

This paper is the second part of a companion paper study focused on the autogenous self-healing capacity of High Performance Fibre Reinforced Cementitious Composites (HPFRCCs). In part 1 investigation has focused on the capacity of the material to completely or partially re-seal the cracks, as a function of its composition, maximum crack width and exposure conditions. Different flow induced alignment of fibres, with respect to the applied bending stresses have been also considered. The outcomes of the self-healing phenomenon, have been analyzed in terms of recovery of stiffness, strength and ductility, as measured by means of 4-point bending tests, performed before (pre-cracking) and after the conditioning exposure. In a durability-based design framework, self-healing indices quantifying the recovery of mechanical properties were also defined and their significance cross-checked. In this paper the crack closure will be evaluated, both through visual image analysis of the healed cracks as well as through a tailored indirect method, proposed by the first authors in a previous study. This method is based on the comparative analysis of the damage evolution curves built for both the pre-cracked and the healed stages from the evaluation of the flexural stiffness. Recovery of mechanical properties will hence be correlated to the identified amount of crack closure. In the authors' opinion, this step represents a fundamental contribution in order to reliably and consistently incorporate the effects of self-healing into tailored durability-based design approaches, based, e.g., on a “healable” crack width threshold concept.

Bond behavior of GFRP bar-concrete interface: Damage evolution assessment and FE simulation implementations

This study presents a bond damage assessment approach for the glass fiber-reinforced polymer (GFRP) bar-concrete interface. The damage evolution equations are proposed based on the strain equivalence principle of damage mechanics, where the variations of the secant modulus of the bond-slip curve are utilized to evaluate the interface deterioration against slip. Numerical analyses are conducted with the ANSYS finite element (FE) program to simulate the bond behavior of pullout test. Nonlinear material behaviors of the GFRP composite and concrete matrix with respect to plain concrete and fiber-reinforced concrete (FRC) are implemented using appropriate constitutive models. The interfacial bond-slip behavior is implemented using nonlinear spring elements. Numerical predictions are validated by the experimental results and compared with the widely used analytical models accounting for the FRP-concrete bond. Upon this, the bond damage evolution curves are derived thereafter, which are found to strictly follow the lognormal distribution or Weibull distribution. Further comparisons of different specimens are performed to investigate the critical factors and their impacts on the damage evolution, as well as those on the critical bond damage corresponding to the bond strength.

Research on the time–temperature–damage superposition principle of NEPE propellant

To describe the relaxation behavior of NEPE (Nitrate Ester Plasticized Polyether) propellant, we analyzed the equivalent relationships between time, temperature, and damage. We conducted a series of uniaxial tensile tests and employed a cumulative damage model to calculate the damage values for relaxation tests at different strain levels. The damage evolution curve of the tensile test at 100 mm/min was obtained through numerical analysis. Relaxation tests were conducted over a range of temperature and strain levels, and the equivalent relationship between time, temperature, and damage was deduced based on free volume theory. The equivalent relationship was then used to generate predictions of the long-term relaxation behavior of the NEPE propellant. Subsequently, the equivalent relationship between time and damage was introduced into the linear viscoelastic model to establish a nonlinear model which is capable of describing the mechanical behavior of composite propellants under a uniaxial tensile load. The comparison between model prediction and experimental data shows that the presented model provides a reliable forecast of the mechanical behavior of propellants.

Experimental study of damage evolution in cuboid stirrup-confined concrete

This paper presents an experimental study on cuboid stirrup-confined concrete specimens under uniaxial monotonic loading and cyclic loading. The effects of stirrup volume ratio, stirrup yield strength, and concrete strength on damage evolution of the stirrup-confined concrete were investigated. The experimental results showed that the strength and ductility of concrete are improved by appropriate arrangement of the stirrup confinement. Firstly, with the increase of the stirrup volume ratio, the damage evolution of concrete can be relatively restrained. Secondly, higher stirrup yield strength usually leads to larger confining pressures and slower damage evolution. In contrast, higher concrete strength leads to higher brittleness, which accelerates damage evolution. Based on the experimental data, a plastic strain expression is obtained through curve fitting, and a damage evolution equation for stirrup-confined concrete is proposed by introducing a confinement factor (C). The comparisons results demonstrated that the proposed damage evolution curve can accurately describe the experimental results.

損傷力学によるニオブ合金材の高温機械特性モデリングとクリープ疲労解析

The elasto-plastic constitutive equation based on the concept of continuum damage mechanics was formulated for the niobium alloy (C103) which is used as a chamber material in a satellite's thruster. The existing theory was extended to deal with the creep fatigue behavior at the high temperature of 1500°C. Creep, tensile and creep fatigue tests (stress-controlled) were conducted with plate bar specimens made of the niobium alloy. The tests were conducted at 1500°C and obtained data were used to determine the material parameters employed in the constitutive equation. Time-strain curves and damage-evolution curves were also simulated and the validity of material parameters was confirmed by comparing calculated values with test results. Creep fatigue life analyses were also conducted and the results were compared with the experimental values. From the results, it is expected that the used constitutive equations and determined material parameters can predict the mechanical features and creep fatigue life for the niobium alloy at the high temperature.

Research on Landscape Limestone Damage and Deformation under Uniaxial Compression Based on Acoustic Emission

In order to establish the relation between acoustic emission parameter and rock mechanical damage mechanism, as well as to better figure out landscape limestone damage and deformation influenced by uniaxial compression, MTS815 rock mechanical electro-hydraulic servo test system and 8CHSPCI-2 acoustic emission and detection system are applied to implement a test and research on damage evolution of limestone under uniaxial compression and the corresponding acoustic emission feature. On this basis, the acoustic emission feature of limestone under uniaxial compression is analyzed. Moreover, based on the damage variable of normalized accumulated emission ringing count, the uniaxial compression limestone damage model based on acoustic emission feature is established, and the damage evolution curve and equation of limestone is figured out as well. Shown by the research, acoustic emission information reflects the internal damage of limestone, and is closely related with densification of inner original fracture, as well as emerging, developing, and merging of new fractures. The acoustic emission feature of limestone perfectly describes its deformation and damage evolution.

Overall mechanical behavior of nanocrystalline materials accompanied by damage evolution on grain boundaries

In the present research, overall mechanical behaviors of the nanocrystalline materials considering the grain boundary damage evolutions are investigated systematically. A mixed-mode cohesive interface model is used to describe the mixed deformation and fracture process of grain boundaries. Based on the mixed-mode cohesive interface model, the grain boundary damage and damage evolution are defined and characterized. In order to describe the size effect, the strain gradient plasticity theory is used for grain materials. In the present results, the overall stress–strain relations and the corresponding damage evolution curves are obtained as functions of several independent parameters, such as the mixed separation strength, the mixed critical energy release rate, grain size, Young’s modulus as well as strain hardening exponent. The present results show that both the overall strength and ductility of the nanocrystalline materials are closely dependent on the grain boundary strength and the damage evolution behaviors. By means of the damage evolution relations, the features of the overall stress–strain curves can be clearly interpreted.

Multi-scale based fracture and damage analysis of steel fiber reinforced concrete

By adding steel fibers into concrete matrix, the strength and toughness of concrete could be well improved especially for high strength concrete. However, despite numbers of recent works to find out the overall mechanical behaviors of high strength fiber reinforced concrete (FRC), the quantitative assessments of load distribution between reinforcement and matrix and fiber bridging for opening cracks are lacking. Thus the present work concentrates on the high strength fiber reinforced concrete in the view of multi-scale analysis. A refined numerical model is developed to simulate the behavior of fiber reinforced concrete in meso-level. The steel fibers are modeled by a large number of truss elements which are randomly distributed within the concrete matrix. The concrete are modeled by 3-D solid element. Based on the stress and strain distributions simulated in the meso-level, the homogenized stress and strain in continuum level are resolved by micro-mechanics. And the homogenized damage evolution curve, which is required for the continuum damage model based structural nonlinear analysis, could be calculated based on the multi-scale damage model. The proposed method offers a hierarchical multi-scale framework to investigate the nonlinear behavior of FRC structure in a considerate way.

Strain and Damage-Based Analytical Methods to Determine the Kachanov–Rabotnov Tertiary Creep-Damage Constants

In the power generation industry, the goal of increased gas turbine efficiency has led to increased operating temperatures and pressures necessitating nickel-base superalloy components. Under these conditions, the tertiary creep regime can become the dominant form of creep deformation. In response, the classical Kachanov–Rabotnov coupled creep-damage constitutive model is often used to predict the creep deformation and damage of Ni-base superalloys. In this model, the secondary creep behavior can be determined through analytical methods while the tertiary creep behavior is often found using trial and error or numerical optimization. Trial and error may produce no constants. Numerical optimization can be computationally expensive. In this study, a strain-based and damage-based approach to determine the tertiary creep behavior of nickel-base superalloys has been developed. Analytically determined constants are found for a given nickel-base superalloy. Creep deformation and damage evolution curves are compared. Methods to deal with stress dependence are introduced and studied.

Ambient and high temperature in situ damage evolution in nickel based IN 718 super alloy

In the present work, Lemaitre's damage assessment methodology has been applied to predict evolution of damage during tensile test at ambient temperature and at 823 K in nickel based IN 718 super alloy. The damage has been evaluated through apparent elastic modulus measurement from each unloading step during the test. Marked difference was found in damage evolution and operative damage micromechanisms at these test temperatures. Critical points have been identified on the damage evolution curves for room temperature loading condition. Based on these parameters, the damage has been predicted using Lemaitre's damage model for high temperature specimen. The damage predicted is found to be in good agreement with experimental curve.

Investigation and modeling on fatigue damage evolution of rock as a function of logarithmic cycle

AbstractThe fatigue damage behavior of granite under constant and variable amplitude loadings is studied. The experimental analysis reveals that there is a three‐stage law for the fatigue damage evolution as a function of absolute or relative cycle and the inverted‐S damage model proposed by the author, in this case, is capable of representing the damage behavior of rock. However, when the logarithmic cycle is considered, there are only two stages, i.e. steady and accelerated stages and the fatigue damage evolution greatly depends on the properties of rock and stress level. Accordingly, the fatigue damage evolution curves have been categorized into three types. Then, the effect of maximum stress, amplitude and fatigue initial damage on the damage evolution of rock is investigated. The analysis reveals that the damage evolution greatly depends on these influencing factors. The fatigue life decreases with the increase in the maximum stress, amplitude and fatigue initial damage due to the decrease in the proportion of the first stage to the whole fatigue process and the increase in the damage rate in the first stage. Meanwhile, a linear‐exponential formula is used to model the fatigue damage behavior of rock subjected to cyclic loading. This damage model is superior to the inverted‐S damage model in the convenience of establishment of critical instability point. The physical meanings of its constants have been illuminated and the applicability of this model to constant and variable amplitude cyclic loading explored. The fitting results for the test data show that this damage model can properly represent the fatigue damage behavior of rock. Copyright © 2010 John Wiley & Sons, Ltd.

Nonlinear dynamic response and fatigue damage evolution for piezoelectric laminated plates with matrix cracks

Based on the Talreja’s damage model with tensor valued internal state variables, considering the effects of piezoelectricity, geometrical nonlinearity and the constitutive relations of the composite uni-ply plate with matrix cracks, the nonlinear dynamic equations of piezoelectric laminated plates with damage are established and the problems are solved by using the finite difference method. In numerical calculating examples, the nonlinear dynamics responses and the fatigue damage evolution curves of the plates are obtained, and the effects of piezoelectric materials, damage and external load on the nonlinear dynamic response and fatigue damage evolution of the plates are discussed.

Fatigue Damage of Asphalt Pavement on an Orthotropic Bridge Deck

ABSTRACT The behavior of asphalt layers on steel bridge decks is extremely complex. Its design for the wearing course on steel decks is important for durability reasons. The steel deck is a soft support as compared to the base course for pavement. The asphalt concrete on a steel deck is subjected to large strain that may generate cracks. A five-point bending fatigue test and a fatigue test on cylindrical specimens have been in development since 2003 at the ENTPE laboratory. The mechanical evolution of the material is monitored with displacement sensors and wave propagation throughout the test. Significant strain increases and decreases are observed when cracks are created and propagated. Velocities and amplitudes of waves decrease clearly as the number of load cycles increases. Under the assumption of linear viscoelasticity, the complex modulus and Poisson's ratio of the asphalt layer are calculated at each instant by inverse analysis, making it possible to plot the damage evolution curve for each asphalt mix tested. A new standard test method is currently being validated.

An energy based damage mechanics approach to modelling impact onto woven composite materials: Part II. Experimental and numerical results

Abstract Laminated composites have found an increasing use in many industries, particularly in transport, e.g. in the design of aircraft, helicopters, boats, cars, etc. Many of these composite components are fabricated from woven carbon based materials, which are more drapeable than conventional uni-directional (UD) composites, but generally have less stiffness and strength. To accurately design such components or structures to withstand severe external loadings, such as high velocity impact or a crash event, is conceptually a difficult task for the composite designer. Unlike metallic components, which can yield and dissipate energy via plasticity, composites can only dissipate energy by different damage or fracturing processes, which usually degrade the stiffness of the structural component. This paper presents the application of the energy based damage model, previously described [Iannucci L, Willows M. An energy based damage mechanics approach to modelling impact onto woven composite materials: Part I Numerical model, Composites A, in press, doi:10.1016/j.compositesa.2005.12.013], suitable for modelling the progressive failure of woven carbon composites under high strain loading. The approach is based on a damage mechanics methodology, and has been implemented into the explicit dynamic DYNA3D code for plane stress shell elements. An interface modelling strategy is also presented to determine the corresponding maximum delamination envelope during a dynamic simulation. The form of the stress–strain–damage curve for woven carbon and the relevance of experimentally measured material damage constants are discussed. The simulation results are compared to three CRAG impact experimental tests at three distinct energy levels. A detailed parameter study is performed on the magnitude of the intralaminar energy release rate used to propagate the damage in woven carbon composites. Conclusions are drawn on the assumed form of the damage evolution curve, and its applicability to stochastic modelling techniques.

Fatigue Life Estimation of Adhesively Bonded Scarf Joints Based on a Continuum Damage Mechanics Model

An estimation method of fatigue strength of adhesively bonded joints with various stress triaxialities in the adhesive layer has been proposed based on a damage evolution model for high cycle fatigue. To realize various triaxial stress states, fatigue test was conducted for adhesively bonded butt and scarf joints with various scarf angles bonded by a rubber-modified epoxy adhesive. An equation for estimating the damage evolution in the adhesive layer of the butt and scarf joints was derived from the damage model, where undefined parameters in the equation were determined by comparing the experimentally obtained damage evolution curves of the butt joints with the estimated damage evolution curves. Furthermore, an equation for the estimation of fatigue strength was derived under the assumption that fatigue failure occurs when the damage variable reaches to a critical value. When compared the experimental S-N data of scarf joints with the estimated ones, the estimated fatigue strengths agree well with the experimental data with various scarf angles. This finding suggests that the CDM model is applicable for estimating fatigue strength of adhesively bonded joints with different stress triaxialities.

Fatigue resistance of continuous glass fiber/polypropylene composites: consolidation dependence

The effect of consolidation on the fatigue resistance of continuous glass fiber/polypropylene (CGF/PP) composites was studied. Five sets of conditions, chosen to approach plant-like processing conditions, were used to obtain samples with varying consolidation quality. These conditions resulted in different void content, degree of crystallinity, size of crystalline entities (spherulites) and level of fiber dispersion. Although they led to different short-term (flexural, tensile or short-beam shear) mechanical results, a single linear correlation could be established between the interlaminar shear strength (ISS) and the void content for all consolidation conditions except one. The fatigue resistance of the CGF/PP composites showed that these consolidation conditions also resulted in different fatigue damage evolution and fatigue resistance curves (or S–N curves). From the S–N curves, two useful correlations could be established: the first is a linear correlation between the Basquin's fatigue strength and the short-term flexural strength; the second is a linear correlation between the Basquin's fatigue sensitivity and ISS. The results emphasize the predominance of the fiber–matrix interface in determining the general mechanical properties of continuous fiber composites and suggest that short-term flexural and short-beam shear tests can be useful empirical indicators of the long-term performance of CGF/PP composites.

Measurement of non-linear microcrack accumulation rates in polymethylmethacrylate bone cement under cyclic loading.

Damage accumulation in the cement mantle used to fixate bone prosthesis is one failure scenario for joint reconstruction. It can be described as the phenomenon of numerous microcracks initiating and propagating within the material. Microcracks grow in the cement mantle causing it to gradually lose its mechanical integrity, leading to loosening of the prosthesis. In this study microcracking within acrylic bone cement was quantified over the course of a fatigue test. Identification of new cracks and the growth of pre-existing cracks was monitored at intervals during fatigue testing of five specimens at a mean cyclic stress of 7.5 MPa. Given these measurements, an average damage evolution curve was derived for acrylic bone cement. It was observed that the initiation sites for microcracks were the pore perimeters; therefore, the number of microcracks present in a sample is dependent on porosity. Variability was found within the results and the majority of the variability was accounted for by the difference in the porosity of each sample. Results have identified non-linear damage evolution. On a simplified level a power law equation can be used to describe the damage evolution process.