Stages Of Damage Evolution Research Articles

Stages of Damage Evolution for Al 2024-T3 Around Fasteners in Marine Atmosphere

Corrosion at fasteners in aluminum presents a high risk and a challenge to corrosion mitigation strategies. The objective of this study was to determine the stages of damage evolution for 2024-T3 around fasteners when exposed at a marine atmospheric corrosion site. A comparison was made between fasteners made from stainless steel, cadmium-plated steel, and cadmium-plated steel with a portion of the plating ground to expose steel and simulate damage to the coating. Corrosion modes were identified over 24-month exposure, and a sequence of corrosion damage stages was developed. Several modes interacted and/or occurred in a sequential pattern. In addition to classic galvanic corrosion, galvanic action had a significant effect on crevice corrosion, intergranular corrosion, and stress corrosion cracking. The important roles of rust on steel fasteners and wedging from the formation of dense corrosion products were identified. Results are relevant to crucial concerns in modeling of damage evolution and developmen...

The effect of TiO 2 as a pigment in a polyurethane/polysiloxane hybrid coating/aluminum interface based on damage evolution

Abstract The effect of titanium oxide as an additive on the performance of a polyurethane/polysiloxane hybrid coating was characterized by an electrochemical approach. The performance evolution was quantified by exposing the hybrid coating on an aluminum substrate to NaCl solution at pH 5 over time. Real-time measurements were performed to quantify and correlate the mechanisms that occur at the coating/substrate interface. Electrochemical impedance spectroscopy (EIS) quantified the hybrid coating/substrate interface performance over the course of the 263 days of exposure, and electrically passive elements described and characterized the degradation/performance stages upon exposure to the acidic NaCl solution. The addition of TiO2 produced hydrophobicity functionality, and TiO2 acted as a physical barrier layer that influenced the initial damage stage. Different exposure times were associated the different stages of damage evolution for the hybrid coating and coating/substrate interfaces. Electrochemical testing with high-resolution techniques such as AFM (atomic force microscope) and IFM (infinite focus microscope) characterized the coating surface and the interface performance and resolved the surface and defect formation observed with different levels of TiO2 content. Of the systems tested, the system with 10 wt% TiO2 provided the best corrosion inhibition.

Meso- and macro-behaviour of coal rock: observations and constitutive model development

Mesoscopic structures must be determined in order to analyse the behaviour of inhomogeneous materials such as coal rock. In this study, a three-dimensional texture of coal rock is scanned by X-ray tomography images using CT system. The time-dependent fracturing behaviour of coal rock for dynamic damage test is then observed by mesoscope under uniaxial stress conditions. In order to determine the dynamic damage evolution process of coal rock, a meso-damage model is introduced, and a constitutive relationship is developed for coal rock subjected to dynamic uniaxial compression in three stages including (I) quasi-linear phase, (II) damage evolution stage and (III) damage accelerating fracture extension. The corresponding meso-mechanical damage mechanisms are investigated.

Notched Fatigue Behavior under Multiaxial Stress States

Most engineering components and structures contain stress concentrations, such as notches. The state of stress at such concentrations is typically multiaxial due to the notch geometry, and/or multiaxiality of the loading. Significant portions of the fatigue life of notched members are usually spent in crack initiation (crack formation and microscopic growth) and macroscopic crack growth. Synergistic complexity of combined stress and stress concentration has been evaluated in a limited number of studies. Available experimental evidence suggests the current life estimation and fatigue damage analysis techniques commonly used may not be capable of accurate predictions for such complex and yet highly practical conditions. This paper investigates notched fatigue behavior under multiaxial loads using aluminum alloys. Many effects involved in such loading conditions are included. These include the effects of stress state (axial, torsion, combined axial-torsion), geometry condition (smooth versus notched), and damage evolution stage (nucleation and micro-crack growth versus long crack growth).

Experimental study of the spatial discontinuity of dynamic damage evolution

In this paper, the damage evolution of high purity aluminum under shock loading is investigated experimentally. The surface profile measurement technique based on white light axial chromatic aberration is used to measure the cross-section of sample which is soft-recovered from dynamic impact experiments. Then, the cross-section image and 3-D surface topography are obtained by reconstruction of the data, the quantified damage is also calculated based on the data. The results show that in the early stage of damage evolution the spatial distribution of relative void volume is not continuous, which results from nucleation affect, size affect and stress relaxation. The damage curves show not only the maximum damage but also a second peak. In the late stage of damage evolution, the spatial distribution of damage increment is discontinuous, which results from the coalescence of voids. The damage of the coalescence region rapidly increases and the secondary peak of the damage curve disappears.

Damage Evolution During Fatigue in Structural Materials

Early stages of damage evolution in cyclic loading are described and discussed. The importance of the role of cyclic plastic strain in damage evolution is emphasized and the relation between stress and strain in cyclic straining is clarified. The principal stages of damage evolution in fatigued crystalline structural material are identified. The basic characteristic and theories of fatigue crack initiation are sketched and confronted with experimental observations. Early fatigue crack growth is characterized and quantitatively described. The relation between the growth of short cracks and fatigue life in the form of Manson-Coffin law is established.

Simulation of Crack Propagation under Small‐Scale Yielding by means of a Non‐local GTN‐Model

AbstractToday, the local approach to fracture is widely applied to simulate the failure of specimens. For ductile damage processes the Gurson‐Tvergaard‐Needleman model is the quasi‐standard. In the last time non‐local extensions allowed a mesh‐size independent simulation of crack growth. However, most publications dealing with this subject focus upon the convergence regarding global quantities such as the load‐displacement relation. Minor attention is paid to the fields directly at the crack tip. Correspondingly, the interrelationship between the intrinsic length of the model and relevant microscopic damage processes at the crack tip is only partly established until now. In the present study the crack propagation is simulated for an implicitly gradient enriched GTN‐model within a boundary layer in order to overcome influences of the specimen geometry. The different stages of damage evolution are resolved by a fine mesh. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Influence of strain rates and load histories on the tensile damage behaviour of concrete

Concrete structures are often subjected to dynamic loads, such as seismic, blast or impact loads. Under such loads, distinct changes may occur in the dynamic and damage behaviour of concrete. This paper presents the results of dynamic tensile tests of plain concrete specimens with axial strain rates ranging from 10−5/s to 10−1/s that were carried out on a servo-testing machine. Observed stages of damage evolution are divided into three phases: undeveloped, steadily developed and unsteadily developed. This study found that the stress threshold ratio of ultimate strength increases with strain rate, and that the initial tangent elastic modulus and Poisson's ratio are independent of the strain rate for the test specimens. Moreover, the tensile strength and critical strain of concrete increased approximately linearly with the logarithm of the strain rate, and an experimental relationship between strain rates and tensile strength, critical strain was established. Furthermore, dynamic tensile damage tests of concrete were carried out with axial strain rates ranging from 10−5/s to 10−2/s. The effects of loading histories on dynamic tensile strengths, dynamic stress–strain curves, and dynamic damage behaviour of concrete were studied. Results indicate that both dynamic tensile strengths and damage thresholds of concrete decreased while the given rated loading was applied compared with those samples that were not subjected to the load history. However, damage of concrete at the same stress ratio and strain ratio increased with the increasing load history.

Microporosity effects on cyclic plasticity and fatigue of LENS™-processed steel

Special microstructures of the newly developed Laser Engineered Net Shaping (LENS™)-processed steel induce a new variability in fatigue damage formation and evolution mechanisms. The microporosity and mechanism of fatigue damage formation and growth were invested using X-ray computed tomography and scanning electron microscopy. Systematic observations were made of the variations in the fracture surfaces according to three fatigue damage evolution stages: fatigue crack formation (incubation), microstructurally/physically small cracks, and long cracks. The fatigue crack was formed almost exclusively at the relatively large pores located at or near the specimen surface, with rare cases at incompletely melted power particles on the surface. Distributed cracks from large interior pores coalesced with each other in the microstructurally small crack regime to form the major critical crack that eventually fractured the specimen. This coalescence accelerated the fatigue crack growth, which in turn decreased the fatigue life but not significantly. In the long-crack regime, the fracture surface was rougher, but the overall surface tended to be perpendicular to the loading direction, indicating a Mode I type fracture. Cyclic strain-softening, with reduced strain-hardening, was also observed. The multistage fatigue model of McDowell et al. was used to capture the microstructure effects in the three fatigue damage evolution regimes, and the upper and lower bounds for the strain–life are predicted.

Damage evolution in a [±45] 2S CFRP laminate under block loading conditions

Cyclic tests were conducted on [±45] 2 S angle ply carbon–epoxy specimens using stress ratios, R (minimum/maximum stress) of 0.1 and −1.0. Damage was monitored by measuring progressive strain changes in the loading direction. The fatigue damage parameter was found to satisfactorily describe the evolution of damage throughout life, facilitating fatigue life prediction. Two distinct stages of damage evolution were identified. In Stage I, the fatigue damage parameter and the density of matrix micro-cracking rapidly increased to a level dependent upon the stress (Characteristic Damage State). This was followed by Stage II which was a long period (∼90% life) of gradual increase in damage, involving crack coalescence, debonding and delamination. On subjecting the specimens to two step block loading tests, synergistic interaction occurred whereby the total fatigue life was greater than that predicted by the summation of the individual blocks of cycles. The effect of crack density and crack closure appeared to play important roles in extending the fatigue life. For the low to high stress level block transition, more cycles were required to reach the Characteristic Damage State, whereas for the high to low sequence, the presence of a large number of cracks and matrix debris within them resulted in closure at the lower stress. Again, the number of cycles to failure increased.

Diagnosis of Artificial Gear Defects on Single Stage Gearbox Using Acoustic Emission

Acoustic Emission is a very powerful tool for health monitoring of structures and mechanical components, especially due to its sensitivity, which is very useful at the early stages of damage evolution. Evaluation of its potential on rotating structures such as gearboxes, is studied in the present paper. A new concept of transducer mounting is realized in a single stage in-house built gearbox. The acoustic emission signature of the healthy gears is acquired. Then artificial defects are seeded and the acquisition is repeated. The signals are afterwards analyzed and the assessment of the applicability of the method becomes possible. Given the present experimental setup, health monitoring of gearboxes using acoustic emission is considered to be of rising potential.

Finite element modelling of damage progression in non-crimp fabric reinforced composites

Progressive failure of non-crimp fabric composite laminate was studied using finite element analysis with stress-based failure criteria. The laminate was loaded in tension and has the lay-up of [0/90] s with both in-phase and out-of-phase placed transverse-tow layers considered. The finite element model was created from a cross-section Representative Volume Element of the laminate. Damage analysis was first carried out using the Maximum Stress failure criterion. After damage was detected within the laminate, point-wise selective stiffness degradation was applied to the model through a user-defined material subroutine. For the material under study, it has been shown that damage initially occurs in either the transverse tows or the resin pockets, and gradually spreads across the transverse tows and resin pockets. As the load reaches a critical point, damage finally progresses into the longitudinal tows and causes laminate failure very quickly. Stages of damage evolution, from initiation until final failure, are reflected in the knee behaviour of the overall load–strain trace. Studies show that tow shape plays a role in the failure progress, especially the load levels for initial and final failure. Analyses using different combinations of failure criteria for the tows and resin pockets were performed and the results were addressed in terms of the location of initial damage and the load levels of initial damage and final failure.

The orientation imaging microscopy of lead-free Sn-Ag solder joints

Orientation imaging microscopy was used to identify solidification microstructures and early stages of damage evolution in tin-silver eutectic solder joints on copper and nickel substrates after aging, creep, and thermomechanical fatigue. A visco-plastic self-consistent plasticity model was able to simulate texture changes when work hardening occurred at higher strain rates, but not with lower rates, where grain boundary sliding dominated the deformation and slip occurred predominantly on one or two slip systems that could be predicted using a Schmid (Sachs) analysis.

A Dynamical Systems Approach to Failure Prognosis

In this paper, a previously published damage tracking method is extended to provide failure prognosis, and applied experimentally to an electromechanical system with a failing supply battery. The method is based on a dynamical systems approach to the problem of damage evolution. In this approach, damage processes are viewed as occurring in a hierarchical dynamical system consisting of a “fast,” directly observable subsystem coupled to a “slow,” hidden subsystem describing damage evolution. Damage tracking is achieved using a two-time-scale modeling strategy based on phase space reconstruction. Using the reconstructed phase space of the reference (undamaged) system, short-time predictive models are constructed. Fast-time data from later stages of damage evolution of a given system are collected and used to estimate a tracking function by calculating the short time reference model prediction error. In this paper, the tracking metric based on these estimates is used as an input to a nonlinear recursive filter, the output of which provides continuous refined estimates of the current damage (or, equivalently, health) state. Estimates of remaining useful life (or, equivalently, time to failure) are obtained recursively using the current damage state estimates under the assumption of a particular damage evolution model. The method is experimentally demonstrated using an electromechanical system, in which mechanical vibrations of a cantilever beam are dynamically coupled to electrical oscillations in an electromagnet circuit. Discharge of a battery powering the electromagnet (the “damage” process in this case) is tracked using strain gauge measurements from the beam. The method is shown to accurately estimate both the battery state and the time to failure throughout virtually the entire experiment.

Cracking paths at the ply interface in a cross-ply laminate

Abstract It has been observed in both ceramic and polymer–matrix composites that the evolution of transverse matrix cracking shows two distinct stages. When tensile stress is applied in the fiber direction of the 0° ply, cracks are formed in the 90° ply at a load level much lower than the ultimate strength of the laminate. As the load increases, more transverse cracks are initiated. At some critical load, the number of cracks ceases to increase; instead, the existing cracks penetrate into the adjacent 0° layers and eventually fracture the 0° fibers. Catastrophic failure becomes imminent when the 0° fibers are broken. The purpose of this paper is to identify conditions under which transverse cracks are deflected into the ply interfaces at the second stage of damage evolution. To this end, the energy release rates for deflection and penetration are used as a criterion to predict the crack growth paths. It is found that the predicted crack path depends on the geometry, the material properties and the degree of damage. Based on this analysis, a crack path prediction diagram is obtained for crack growth at the ply interface.

Fatigue analysis for analytically overloaded piping components and valves in nuclear power plants: Charalambus, B. Nucl. Eng. Des. (Nov. 1992) 137 (3) 449–455

Special microstructures of the newly developed Laser Engineered Net Shaping (LENS™)-processed steel induce a new variability in fatigue damage formation and evolution mechanisms. The microporosity and mechanism of fatigue damage formation and growth were invested using X-ray computed tomography and scanning electron microscopy. Systematic observations were made of the variations in the fracture surfaces according to three fatigue damage evolution stages: fatigue crack formation (incubation), microstructurally/physically small cracks, and long cracks. The fatigue crack was formed almost exclusively at the relatively large pores located at or near the specimen surface, with rare cases at incompletely melted power particles on the surface. Distributed cracks from large interior pores coalesced with each other in the microstructurally small crack regime to form the major critical crack that eventually fractured the specimen. This coalescence accelerated the fatigue crack growth, which in turn decreased the fatigue life but not significantly. In the long-crack regime, the fracture surface was rougher, but the overall surface tended to be perpendicular to the loading direction, indicating a Mode I type fracture. Cyclic strain-softening, with reduced strain-hardening, was also observed. The multistage fatigue model of McDowell et al. was used to capture the microstructure effects in the three fatigue damage evolution regimes, and the upper and lower bounds for the strain–life are predicted.

Material response at hypervelocity impact conditions using laser induced shock waves

Dynamic fracture at hypervelocity impact conditions was investigated in different materials using short pulsed laser induced shock waves. All stages of damage evolution were identified for one dimensional or spherical shock wave impact geometry. A new experimental method is presented to estimate the shock pressure decay in materials. In the theoretical section we obtain the damage induced in the target, as follows: The shock wave is modeled by an expanding stress front, which creates micro-damage in the laser impacted layer and extrudes a bulge at the far surface. The calculated bulge geometry compares well with that observed by us for metal-adhesive-metal sandwiches. The micro-defects coalesce into macro- damage or fracture by a mechanism which is described by percolation theory.

Laser-induced spall in metals: Experiment and simulation

Spall at ultra high strain rate (107 s−1) was investigated using short pulsed laser-induced shock waves in copper and aluminum foils. The intensities of the 3.9-ns Nd:Glass laser were in the range of 1010–1012 W/cm2, and the foil thickness was in the 100–600 μm range. The laser-generated shock wave pressure was in the range of a few hundred kilobars (kb). The shock wave traversed the foils in a few tens of nanoseconds. The controlled stepwise increase in laser energies allowed the stages of damage evolution from incipient to complete perforation of the target foils to be found. The energy threshold for spall and the spall width at that energy was measured as a function of the foil thickness for both materials. At threshold energy conditions, spall width of 25–65 μm for Al and 15–45 μm for Cu were obtained for foil thicknesses of 100–600 μm. Computer simulations of the laser-induced spall were performed, including the laser absorption, shock wave travel through the foil, and the spall phenomena. The simulations were based on the one-dimensional medusa code, which was expanded to include the spall phenomena, using simple spall criteria. An estimate of the strain rate was derived from the simulations and it was shown that the strain rates in the present experiments are about an order of magnitude larger than those obtained in spall experiments using other methods. The experimental results of energy threshold for spall and spall width at this energy were compared with the numerical simulations. The experimental results are in good agreement with the simulation results, indicating that spall strength for both materials, Al and Cu, are in the −50 to −60 kb regime.

On the spatial characterization of damage evolution by a one-dimensional model

Damage diffusion, concentration and localization are investigated by introducing a small non-uniform initial damage in the material. Several parameters characterizing the local and global damage non-uniformities are defined mathematically, and relations are established between these parameters and the constitutive laws for damaged materials through a simple one-dimensional calculation. The influence of damage non-uniformity on the material failure is illustrated by a quantity termed rupture toughness, defined as the specific plastic work the material can absorb prior to failure. Six continuum damage models are examined for their damage distribution characteristics by means of this methodology. For rate independent processes under stress controlled loading, the damage models based solely on the effective stress, such as the models advanced by Broberg ( J. appi. Mech. 41, 809, 1974) and by Roussiler (contribution to the research of fracture of metals in the elastic-plastic fields. Thesis of Ecole Polytech., Univ. Paris, 1979), show damage localization at a relatively low damage level, and a global concentration on both damage and plastic deformation fields. The same features are incorporated in Gurson's model ( J. Engng Mater. Tech. 99, 2, 1977) provided void nucleation is ignored. As to the creep damage processes, the phenomenological theory of Kachanov ( Ivz. Akad. Nauk., S.S.R., Otd. Tech. Nauk., No. 8, 1958) shows a range of damage distribution behaviour according to the ranges of its parameters and initial damage distribution. Damage diffusion prevails for creep damage growth controlled by grain boundary diffusion ( Cocks and Ashby, Prog. Mater. Sci. 27, 189, 1982). For the creep damage processes controlled by surface diffusion ( Cocks and Ashby, 1982), however, damage localization occurs at an early stage of damage evolution.