Rate Of Damage Accumulation Research Articles

A computational framework for the analysis of rain-induced erosion in wind turbine blades, part II: Drop impact-induced stresses and blade coating fatigue life

With the current trend in wind energy production, the need to manufacture larger wind turbine blades is on the rise. The high blade tip velocities associated with large blades subject them to various damages due to high speed impact with foreign objects such as raindrops. This paper is the second part in a two-part paper that presents a framework for rain erosion prediction in wind turbine blades. In part I, a stochastic rain texture model and multi-resolution simulation of raindrop impact on solid object were discussed. In part II, the predicted impact pressure profiles are imported into a finite element model of the wind turbine blade shell to analyze the raindrop impact-induced transient stresses within the blade coating and the ensuing fatigue damage pattern. The analysis is complemented with a fatigue stress-life estimation process that integrates elements of fatigue life calculation with 3D fields of raindrops generated from the stochastic rain texture model to relate damage accumulation rates to rain intensities. These accumulation rates, together with the statistics of rainfall history, provide a means for estimating the expected fatigue life of the blade coating as an indication of the onset of surface roughening or the end of the incubation period.

The role of tension-compression asymmetry of the plastic flow on ductility and damage accumulation of porous polycrystals

The influence of the tension-compression asymmetry of the plastic flow, due to intrinsic single-crystal deformation mechanisms, on porosity evolution and the overall ductility of voided metallic polycrystals is assessed. To this end, detailed micromechanical finite-element analyses of three-dimensional unit cells containing a single initially spherical cavity are carried out. The plastic flow of the matrix (fully-dense material) is described by a criterion that accounts for strength-differential effects induced by deformation twinning of the constituent grains of the metallic polycrystalline materials. The dilatational response of porous polycrystals are calculated for macroscopic axisymmetric tensile loadings corresponding to a fixed value of the stress triaxiality and the two possible values of the Lode parameter. It is shown that damage accumulation, and ultimately ductility of the porous polycrystals are markedly different as compared to the case when the matrix is governed by von Mises criterion. Most importantly, a direct correlation is established between the macroscopic material parameter k that is intimately related to the particularities of the plastic flow of the matrix and the rate of damage accumulation.

Fatigue life prediction of composite material's adhesive joints in automotive applications

Composite and adhesive joints are used increasingly in the automotive industry, not only because of the government policy but also their advantages in mechanical properties over traditional materials and joints. An active research area is the fatigue analysis of adhesive joints. In this paper, a methodology to predict the fatigue life of adhesive joint is proposed and implemented into LS-DYNA with the joint modelled using a user-defined cohesive material. Fatigue crack growth rate is used to obtain the fatigue damage accumulation rate in cohesive zone model. Our method is verified by numerical simulations of two commonly used adhesive joints in the automotive industry: single-lap joint and stepped-lap joint. The predicted S-N curve fits well with the experimental data.

Investigation on fatigue behaviors of NiTi polycrystalline strips under stress-controlled tension via in-situ macro-band observation

One of the challenging issues in studying the fatigue behaviors of NiTi shape memory alloy is the interaction between the material damage and material's martensitic phase transformation which takes place in a macroscopic homogeneous mode or a heterogeneous mode (forming macro-domains like Lüders bands). In this paper, we conducted systematic experiments on NiTi polycrystalline strips under stress-controlled cyclic tensile loadings with in-situ optical observation on the Lüders-band evolution. It is found that the applied stress level and frequency influence the band formation changing the material's fatigue behaviors significantly. The band evolution divides a specimen into “non-active zones” (with the “elastic” deformation of Austenite or/and Martensite) and “active zones” (with the cyclic phase transformation) where fatigue failure occurs. Based on the local strain measurement by Digital Image Correlation, the local residual-strain (damage) accumulation rate is determined and found to have a good correlation with the material's fatigue life. Our results would be helpful for further understanding and modeling the material's stress- and frequency-dependent fatigue behaviors.

MEMS Packaging Reliability in Board-Level Drop Tests Under Severe Shock and Impact Loading Conditions—Part II: Fatigue Damage Modeling

Damage in handheld electronic devices due to accidental drops is a critical reliability concern. This paper is the second of a two-part series and focuses on damage models for drop test durability of commercial off-the-shelf microelectromechanical systems (MEMS) components that are mounted on printed wiring boards. The modeling approach is based on the experimental results presented in the first part of this two-part series. In particular, the focus of this paper is on damage due to drop events under extremely high accelerations (20 $000g$ , where $g$ is the gravitational acceleration) achieved by a series of secondary impacts. Impacts with such high accelerations can occur in handheld electronic devices due to collisions between internal neighboring structures and can generate stress levels well beyond levels previously anticipated in typical use, or in conventional qualification tests. A calibrated dynamic multiscale finite element model is used to evaluate the stresses at the relevant failure sites. Utilizing the local stress at each failure site, a fatigue damage modeling approach is proposed to predict the interaction of the competing failure mechanisms in MEMS components. The proposed damage model is based on the deviatoric stress (or strain) at the failure site and uses a hydrostatic stress correction factor to address the influence of mean stress (depending on component orientation). The model estimates the damage accumulation rate for a given stress condition and integrates the accumulated damage over the entire response history. This approach makes it possible to address the influence of the post-impact transient response on fatigue damage accumulation. The damage-model constants are determined for each failure site of interest by relating the failure data to the corresponding stress/strain metrics. Damage modeling results are not only capable of matching the lifetimes of MEMS components in drop testing, but also provide an explanation of transitions in dominant failure sites observed in MEMS assemblies under different drop conditions.

Effects of the cooling rate on the shear behavior of continuous glass fiber/impact polypropylene composites (GF-IPP)

Fiber-reinforced composites with improved dissipation of energy during impact loading have recently been developed based on a polypropylene copolymer commonly called impact polypropylene (IPP). Composites made of IPP reinforced with glass fibers (GF) are particularly attractive to the automotive industry due to their low cost and good impact resistance. In such composites, the cooling rate varies depending on processing techniques and manufacturing choices. Here, we study the effects of the cooling rate of GF-IPP composites on shear behavior, which is critical in impact applications, using [±45]s monotonic and cyclic (load/unload) tensile specimens. The specimens were manufactured under a wide range of cooling rates (3°C/min, 22°C/min, 500–1000°C/min). Mainly dominated by the properties of the matrix, the global shear behavior of GF-IPP composites differed considerably with respect to the cooling rate. However, the performance of the fiber-matrix interface (chemically modified) appeared to be unaffected by the range of cooling rates used in this study. We found that the cooling rate has a minor effect on the rate of damage accumulation, while it strongly modifies the shear-activated rate-dependant viscoelastic behavior.

Determination of Fatigue Resistance Characteristics Based on High-Frequency Testing Results Considering Structural and Operational Factors

The experimental investigations of the fatigue resistance of various metallic materials were conducted loading in the range of frequencies from a few Hz to 10 kHz with account of the material structure, test temperature, load ratio and availability of stress concentrators. It is shown that the influence of the most process, structural and operational factors on the values of endurance limits manifests itself identically at both low and high loading frequencies. This implies that the main mechanisms of fatigue damage accumulation intrinsic to the particular material remain independent of loading frequency, while deformation rate affects the value of inelastic strains and, consequently, the degree of plastic strain accumulated during a cycle and endurance limit values. The equation is proposed, which describes the material state at the instant of time preceding the fatigue crack growth initiation with account of the cyclic loading frequency as a factor controlling the damage accumulation rate. An experimental verification of the obtained equation showed that difference between the calculated and experimental data on the fatigue resistance is, as a rule, within the experimental data scattering, which confirms the sustainability of the model. The proposed model provides the base for the prediction of the fatigue resistance characteristics, including at large number of cycles, at various frequencies based on high-frequency test results.

A remarkable improvement of low-cycle fatigue resistance of high-Mn austenitic TWIP alloys with similar tensile properties: Importance of slip mode

The low-cycle fatigue (including extremely-low-cycle fatigue) behaviors of the FeMnC TWIP steels are comprehensively investigated focusing on the effects of the imposed strain amplitude and Mn content on the deformation and damage characteristics. It is found that fatigue performance varies obviously with increasing Mn content, though their tensile properties do not change much. With the increase of strain amplitude or Mn content, the dislocation slip mode changes from planar slip to wavy slip. In order to evaluate the low-cycle fatigue properties, more impartial and reasonable, a hysteresis energy-based fatigue life prediction model is applied and developed. According to the experimental results and model analysis, unlike tensile properties, the low-cycle fatigue performance of the TWIP steel is extremely sensitive to their slip mode. A remarkable improvement of fatigue resistance is found to be related to the increase of Mn content, which may originate from the relatively low damage accumulation rate of planar slip. Specifically, planar slip caused by lowering the stacking fault energy is much more uniformly distributed than which caused by disordering short-range order. Such a variation in fatigue damage micromechanisms is believed to be the major reason for the occurrence of a special bilinear relationship for the Coffin-Manson curve.

Modeling of fatigue damage of coated bodies under frictional loading

A model of contact fatigue damage of a coated body in high-cycle friction performed using a periodic system of indenters has been proposed. The influence of wear of non-fatigue origin on damage accumulation in the coating and substrate is studied. It is shown that the rate of damage accumulation in the coating decreases but remains unchanged or increases at the coating-substrate interface. Comparison of results for a constant and stochastically time-varying pressure distribution shows that variable loading increases the number of detachments of finite-thickness layers and inhibits contact fatigue damage accumulation at the interface.

Mitochondrial health, the epigenome and healthspan.

Food nutrients and metabolic supply-demand dynamics constitute environmental factors that interact with our genome influencing health and disease states. These gene-environment interactions converge at the metabolic-epigenome-genome axis to regulate gene expression and phenotypic outcomes. Mounting evidence indicates that nutrients and lifestyle strongly influence genome-metabolic functional interactions determining disease via altered epigenetic regulation. The mitochondrial network is a central player of the metabolic-epigenome-genome axis, regulating the level of key metabolites [NAD(+), AcCoA (acetyl CoA), ATP] acting as substrates/cofactors for acetyl transferases, kinases (e.g. protein kinase A) and deacetylases (e.g. sirtuins, SIRTs). The chromatin, an assembly of DNA and nucleoproteins, regulates the transcriptional process, acting at the epigenomic interface between metabolism and the genome. Within this framework, we review existing evidence showing that preservation of mitochondrial network function is directly involved in decreasing the rate of damage accumulation thus slowing aging and improving healthspan.

Effects of alternative polymer modifications on cracking performance of asphalt binders and resultant mixtures

The use of styrene-butadiene-styrene (SBS) polymer-modified asphalt (PMA) binder has successfully enhanced pavement cracking performance. Meanwhile, state agencies hesitate to allow the use of alternative PMA binders that meeting existing specification requirements for PG 76-22 SBS PMA binder, due to a lack of experience and documented performance. A previous study identified four out of seven alternative PMA binders that exhibited excellent elastomeric behavior and fracture properties. This study extends these prior efforts by assessing whether binder results translate to improved cracking performance of resultant mixtures. Superpave indirect tension (IDT) tests were conducted to obtain the fracture properties of asphalt mixtures with the four alternative PMA binders, as well as a standard PG 76-22 (3% SBS) PMA binder and a PG 67-22 unmodified base binder. Results showed that these alternative PMA binders, produced with SBS plus polypropylene composite, terpolymer plus polypropylene composite, SBS plus oxidized polyethylene wax and a fourth non-SBS polymer of unknown composition, not only reduced the rate of damage accumulation but also improved the failure limit of the resultant mixtures. The energy ratio (ER) parameter which has been closely tied to field pavement cracking performance was calculated for each mixture, and the results showed that these alternative PMA binder exhibited equivalent or better cracking performance than the PG 76-22 SBS PMA binder. Finally, the binder fracture energy density (FED) results satisfactorily rank mixture cracking performance thereby supporting the use of the binder fracture energy (BFE) test as an effective tool to quantitatively evaluate the relatively cracking performance of asphalt binder.

Evaluating the heat energy dissipated in a small volume surrounding the tip of a fatigue crack

Fatigue crack initiation and propagation involve plastic strains that require some work to be done on the material. Most part of this irreversible energy is dissipated as heat and consequently the material temperature increases. The heat being an indicator of the intense plastic strains occurring at the tip of a propagating fatigue crack, the hypothesis is formed that it can be used to assess the fatigue damage accumulation rate of cracked components. Moreover, the heat energy at the crack tip is averaged according to Neuber’s finite particle concept. The aim of the present paper is to present the theoretical framework and the corresponding experimental technique to evaluate the heat energy dissipated in a structural volume surrounding the crack tip. The shape and size of the structural volume have been assumed according to the literature, even though the definition of the structural volume size of the analysed material in a fatigue sense is not the scope of the present paper. The proposed experimental technique to evaluate the averaged heat energy is based on the radial temperature profiles measured around the crack tip by means of an infrared camera. The temperature fields measured within few millimetres from the crack tip have been compared successfully with existing analytical solutions.

Temperate marine herbivorous fishes will likely do worse, not better, as waters warm up

Increased temperatures are associated with reduced body sizes, life spans, and reproductive outputs in shallow water marine fishes, reflecting the pervasive effects of temperature on metabolic rates in ectotherms. Herbivorous fishes have been seen as an exception to this trend, based on the hypothesis that physiological and demographic processes in these species are constrained by the inability to digest algae at low temperatures. It is thus argued that increased temperatures deliver a net benefit to herbivorous fishes. This study examines an alternative argument, that warming temperatures can have increasingly inimical effects on temperate piscine herbivores. We consider the hypothesis that herbivores experience greater oxidative stress at warmer temperatures, a consequence of temperature-related increases in metabolic rates. We use the age pigment lipofuscin to examine the rate of oxidative damage accumulation in populations of a temperate marine herbivorous fish, Odax pullus (Labridae), at different latitudes (temperatures) across New Zealand (175.3°E, 36.3°S–167.9°E, 47°S). We show a 55 % faster rate of oxidative damage accumulation in shorter-lived fish living at warmer latitudes. In these populations, it took 33–50 % fewer years to accumulate similar amounts of oxidative damage than in those living at colder latitudes, indicating greater oxidative stress in fish living at warmer temperatures. We conclude that at least some temperate piscine herbivores will be exposed to negative demographic impacts at their low-latitude range margins as temperatures increase.

Experimental estimation of the heat energy dissipated in a volume surrounding the tip of a fatigue crack

Fatigue crack initiation and propagation involve plastic strains that require some work to be done on the material. Most of this irreversible energy is dissipated as heat and consequently the material temperature increases. The heat being an indicator of the intense plastic strains occurring at the tip of a propagating fatigue crack, when combined with the Neuber’s structural volume concept, it might be used as an experimentally measurable parameter to assess the fatigue damage accumulation rate of cracked components. On the basis of a theoretical model published previously, in this work the heat energy dissipated in a volume surrounding the crack tip is estimated experimentally on the basis of the radial temperature profiles measured by means of an infrared camera. The definition of the structural volume in a fatigue sense is beyond the scope of the present paper. The experimental crack propagation tests were carried out on hot-rolled, 6-mm-thick AISI 304L stainless steel specimens subject to completely reversed axial fatigue loading.

Low-cycle and extremely-low-cycle fatigue behaviors of high-Mn austenitic TRIP/TWIP alloys: Property evaluation, damage mechanisms and life prediction

The cyclic deformation and damage behaviors of the Fe–Mn and Fe–Mn–C TRIP/TWIP steels are comprehensively studied in a wide range of strain amplitude (from 0.3% to 8.0%). It is found that with increasing C content, the dislocation structures change from wavy slip to planar slip after cyclic deformation. In order to evaluate the low-cycle and extremely-low-cycle fatigue (LCF and ELCF) properties, a fatigue life prediction model, Nf = (Wa/W0)β, with a hysteresis energy-based criterion is used and developed. The model reveals that the LCF and ELCF damage mechanisms can be controlled by the material's damage capacity (the intrinsic fatigue toughness W0) and its ability of transforming mechanical work into effective damage (the damage transition exponent β). From a macroscopic point of view, W0 is related to the match of strength and ductility (approximately the static toughness U), and β mainly has a negative correlation with the cyclic strain hardening exponent n′. On the micro-scale level, W0 represents the defect-accommodated ability of the materials, and β is determined by the uniformity and reversibility of plastic deformation. For the current Fe–Mn(–C) TRIP/TWIP steels with increasing C content, the cooperation between an increasing damage capacity and an incremental damage accumulation rate leads to a higher ELCF property and a lower LCF property.

PEDICLE SCREW CONVERGENCE IMPACT ON THE STABILITY OF TRANSPEDICULAR FIXATION SPINE MODEL IN CYCLIC LOADING: BIOMECHANICAL STUDY

The principle of this study is experimental measurement and description of behavior of transpedicular fixation during cyclic loading due to convergence of screw insertion. Investigations were made of three configurations of assemblies of posterior stabliization with converging screws at 0°, 20° and 40°. The experiment was inspired ASTM Standard F1717 and modified to minimize the effect of other parameters. The MTS 858.2 Mini Bionix testing system was used during the experiment, in conjunction with the Interface 1010ACK load cell. Data processing and analysis were carried out by Matlab R 20102b, MathWorks. The probed assemblies were cyclically loaded until structural failure occurred, always at the screwbone (or PUR block) interface, i.e., the "windshield wiper" effect. The measurement results show that while the rigidity of the assembly increases with increased convergence of transpedicular screws, they also indicate an increased initial rate of assembly damage accumulation, together with assembly failure during a reduced number of cyclic loading cycles. The mechanical behavioral study of transpedicular fixation is limited by the conditions of simplification of interpretation of complex movements and spinal pathophysiology in the attempt to minimize the effect of other parameters and exaggerated measurements.

Effects of hydromechanical loading history and antecedent soil mechanical damage on shallow landslide triggering

AbstractEvidence suggests that the sudden triggering of rainfall‐induced shallow landslides is preceded by accumulation of local internal failures in the soil mantle before their abrupt coalescence into a landslide failure plane. The mechanical status of a hillslope at any given time reflects competition between local damage accumulated during antecedent rainfall events and rates of mechanical healing (e.g., rebonding of microcracks and root regrowth). This dynamic interplay between damage accumulation and healing rates determines the initial mechanical state for landslide modeling. We evaluated the roles of these dynamic processes on landslide characteristics and patterns using a hydromechanical landslide‐triggering model for a sequence of rainfall scenarios. The progressive nature of soil failure was represented by the fiber bundle model formalism that considers threshold strength of mechanical bonds linking adjacent soil columns and bedrock. The antecedent damage induced by prior rainfall events was expressed by the fraction of broken fibers that gradually regain strength or mechanically heal at rates specific to soil and roots. Results indicate that antecedent damage accelerates landslide initiation relative to pristine (undamaged) hillslopes. The volumes of first triggered landslides increase with increasing antecedent damage; however, for heavily damaged hillslopes, landslide volumes tend to decrease. Elapsed time between rainfall events allows mechanical healing that reduces the effects of antecedent damage. This study proposed a quantitative framework for systematically incorporating hydromechanical loading history and information on precursor events (e.g., such as recorded by acoustic emissions) into shallow landslide hazard assessment.

A regularized Miner’s rule for fatigue reliability analysis with Mittag-Leffler statistics

This paper aims to develop a regularized Miner’s rule to assess the fatigue reliability of composites in conjunction with the Mittag-Leffler Monte Carlo method. The proposed strategy is validated by analyzing experimental data to investigate the fatigue reliability of carbon fiber/epoxy composites under different stress amplitudes. The estimated results are feasible for preliminary analysis at the design stage. The regularized Miner’s rule, a scale transform of fatigue life simulations, accurately describes the damage accumulation rate. It is stressed that the Mittag-Leffler Monte Carlo method is mathematically simple and easy-to-program for researchers and nonexpert engineers.

Effect of heavy ion irradiation on microstructural evolution in CF8 cast austenitic stainless steel

The microstructural evolution in ferrite and austenitic in cast austenitic stainless steel (CASS) CF8, as received or thermally aged at 400 °C for 10,000 h, was followed under TEM with in situ irradiation of 1 MeV Kr ions at 300 and 350 °C to a fluence of 1.9 × 1015 ions/cm2 (∼3 dpa) at the IVEM-Tandem Facility. For the unaged CF8, the irradiation-induced dislocation loops appeared at a much lower dose in the austenite than in the ferrite. At the end dose, the austenite formed a well-developed dislocation network microstructure, while the ferrite exhibited an extended dislocation structure as line segments. Compared to the unaged CF8, the aged specimen appeared to have lower rate of damage accumulation. The rate of microstructural evolution under irradiation in the ferrite was significantly lower in the aged specimen than in the unaged. This difference is attributed to the different initial microstructures in the unaged and aged specimens, which implies that thermal aging and irradiation are not independent but interconnected damage processes.

Remaining Creep Life Assessment of Service Superheat Tube Boiler

The demand of remaining life assessment of the boilers arises from technical, economic, and legal reasons. Creep is major damage mechanism of primary superheat tube boiler during prolong operation at high temperature and pressure in a water tube boiler. This paper presents the calculation method for the remaining life assessment due to creep damage. The service-exposed primary superheat tube made of 2.25Cr-1Mo steels. During scheduled inspection, wall thickness measurement, metallographic investigation by replica technique, design data and operating condition were used to estimate the remaining life in the form of creep damage accumulation rate calculated from life fraction using Larson-Miller Parameter. The results indicate that the primary superheat tubes satisfy in extension service life. By attaining an accurate and timely discussion of the results, the engineer can manage the maintenance and inspection schedule for the critical part in the boiler.