Damage Accumulation Process Research Articles

Fatigue damage accumulation modelling of critical components subjected to moving crane loads in reinforced-concrete industrial buildings

The present work aims to formulate a numerical procedure for modelling fatigue damage accumulation in critical components of reinforced-concrete industrial buildings. Preliminary hierarchical structural-level finite element analysis is performed to locate the critical components. Regularly identified are the RC beams subjected to moving crane loads. Based on an extended damage model for high-cycle fatigue problems, investigated are the RC beams subjected to moving crane loads with constant and variable amplitude. In order to accommodate the practical scenarios, a case of accidental loading is further studied. The simulated process of fatigue damage accumulation is designated up to 70 years of operation. The results show, compared to the case of constant amplitude, the fatigue damage evolution in RC beam increases appreciably when subjected to variable amplitude. The phenomenon of structural deterioration is particularly highlighted in the case of variable amplitude after long-term operation. Furthermore, accidental overloading has appreciable impact on the fatigue damage accumulation of RC beams, which aggravates the structural deterioration. The work provides a numerical framework for damage prognosis and safety assessment on the RC buildings that have been in service for decades under a variety of loading scenarios.

Analysis of Cumulative Damage for Shared Rock in a Neighborhood Tunnel under Cyclic Blasting Loading Using the Ultrasonic Test

In blasting excavation of neighborhood tunnels, damage accumulation process in surrounding rock is inevitable. To explore the influence of damage accumulation of rock mass under multiple blasting loads, we analyzed the vibration damage accumulation process of ultrasonic wave velocity of rock mass in shared rock of Liuyuetian neighborhood tunnel through ultrasonic test. Moreover, the effects of cyclic blasting loads on damage to the shared rock in the neighborhood tunnel were discussed and reported. The results demonstrate that the damage accumulation to the shared rock in the neighborhood tunnel is generated after multicycle progressive blasting operations. Influenced by cyclic blasting loads during the posterior excavating tunnel, the damage range of shared rock at the anterior excavating tunnel is 1.2 to 1.4 m, and the damage range of shared rock at the posterior excavating tunnel is 2.2 to 2.4 m. The damage range of shared rock in the posterior excavating tunnel is about 1.71 to 1.83 times that in the anterior excavating tunnel. Under blasting load, the stress concentration zone of shared rock is close to the blasting excavating face and is mainly within 2 m along the longitudinal axis of the tunnel. With continuous advancement of the blasting excavating face, the stress concentration zone moves forward continuously, and a striped stress concentration zone, which is approximately 2 m deep, is formed gradually. Thus, a method was proposed to determine the damage range of shared rock in the neighborhood tunnel during blasting excavation, as well as the variation law of damage. The experiences and conclusions presented can be used as references in the design and construction of similar engineering projects in the future.

Influence of Filler Crystal Sizes on Acoustic Emission Parameters during Tensile Testing of Parts Made of Plasticized HMX

We study changes in the parameters of acoustic emission that develops during quasistatic deformation of parts made of plasticized coarse- and fine-grained HMX under tension. Characteristic changes in acoustic emission dependences and absolute values of acoustic emission parameters have been determined during transition from a coarse- to a fine-grained material structure. In accordance with the results of the experiments, we analyze possible scenarios of the development of the process of damage accumulation and failure of parts with a change in the size of crystals that form their internal structure. As a confirmation of the corresponding changes in the parameters of acoustic emission, we have investigated the structure of the surface of parts in the zones of their failure using an electron microscope. Under tension, the failure of parts based on finely dispersed HMX occurs instantly, when a critical level of damage is reached in any part of the volume and conditions are created for microcracks to combine into macrocracks. For parts containing coarse HMX, failure typically occurs according to the principle of a “weak” link, ie., localization of microcracks in one or several zones over the volume of the deformed material as early as at the initial stage of loading. These zones become the spots where cracks merge and the focus of their further development up to failure at a new scale level. The results obtained expand the existing understanding of the process of damage accumulation and failure of energy-yielding materials and can be used in the development and improvement of relevant mathematical models.

The Dynamic Reliability Model under Variable Loads and Accelerated Tests

In this paper, we propose a new formulation of the physical reliability principle and build a reliability model in the form of a system of differential equations taking into account variable loads. A load is applied to the input of the dynamic system, and a probability function of failure-free operation is formed at its output. The conditions for the equivalence of dynamic models are studied. In the presence of self-similarity of damage accumulation processes, the general dynamic model is reduced to an equivalent simplified basic dynamic model. The results obtained can be used in the theory of reliability of systems with variable loads, in the analysis of survival, and in the theory of accelerated and forced tests.

Using Methods of Analysis of Optical Images of Friction Surfaces of Ti–Al–N Based Coatings for Assessing Accumulation of Damage and Diagnostics of Failure in Tribological Tests

The processes of damage accumulation and failure in thin ceramic coatings based on the Ti–Al–N system deposited on ductile steel and brittle sitall substrates have been investigated during tribological tests under dry friction conditions. Fractal analysis was carried out to quantitatively assess damage to friction surfaces, as well as Fourier and wavelet analysis of their images obtained using optical microscopy. It is shown that the spectral analysis (Fourier and wavelet analysis) make it possible to reveal an unambiguous correlation between the quantitative parameters obtained and the rate of wear of coatings at the stage of steady wear. At the same time, the fractal dimension provided an estimate of the dynamics of accumulation of damage at the run-in stage but did not allow one to be produced at the stage of steady-state wear.

Damage accumulation analysis of cfrp cross-ply laminates under different tensile loading rates

This paper investigates the loading rate effect on both mechanical properties and damage accumulation process of [0°2/90°4]S carbon fiber-polymer laminates under tensile loading. In-situ edge observations, Acoustic Emission and Digital Image Correlation techniques were utilized simultaneously to monitor the state of damage in real time. Results showed that the axial modulus and strength were less sensitive to loading rates than failure strain, which increased with the decrease of the loading rate. In the viewpoint of damage accumulation process, high density and uniform distribution of transverse matrix cracks, and H-shape crack patterns, incorporating inter-laminar cracks, were more likely to occur at low loading rates while variable crack spacing occurred at higher rates. When loading rates were lower than a certain level, maximum transverse matrix crack density decreased slightly due to the restriction of relatively widely generated inter-laminar cracks. Furthermore, the cumulative acoustic emission energy of low-frequency signals was linearly correlated to transverse matrix crack density, providing a promising way to quantify crack accumulation in real time. Finally, spatial consistence was observed between transverse matrix cracks at edges and stress concentrations at the exterior 0° ply, and the peaks of axial strain at local concentration regions locate either near the newest cracks or at the place with minimum crack spacing.

Unfolding the early fatigue damage process for CFRP cross-ply laminates

This study investigates the early fatigue damage of cross-ply carbon/epoxy laminates. The aim is to unfold the damage accumulation process, understand the interaction between different damage mechanisms, and quantify their contribution to stiffness degradation. Tension-tension fatigue tests were performed, while edge observation and DIC technique monitored the damage evolution. It was found that different accumulation process and interactive levels between transverse matrix cracks and delamination exist for specimens with similar stiffness degradation. A linear increase of stiffness degradation was observed with the increase of matrix crack density, while the growing trend of stiffness degradation converged with the increase of delamination.

Exponential increase in mortality with age is a generic property of a simple model system of damage accumulation and death.

The risk of dying increases exponentially with age, in humans as well as in many other species. This increase is often attributed to the "accumulation of damage" known to occur in many biological structures and systems. The aim of this paper is to describe a generic model of damage accumulation and death in which mortality increases exponentially with age. The damage-accumulation process is modeled by a stochastic process know as a queue, and risk of dying is a function of the accumulated damage, i.e., length of the queue. The model has four parameters and the main characteristics of the model are: (i) damage occurs at random times with a constant high rate; (ii) the damage is repaired at a limited rate, and consequently damage can accumulate; (iii) the efficiency of the repair mechanism decays linearly with age; (iv) the risk of dying is a function of the accumulated damage. Using standard results from the mathematical theory of queues it is shown that there is an exponential dependence between risk of dying and age in these models, and that this dependency holds irrespective of how the damage-accumulation process is modeled. Furthermore, the ways in which this exponential dependence is shaped by the model parameters are also independent of the details of the damage accumulation process. These generic features suggest that the model could be useful when interpreting changes in the relation between age and mortality in real data. To exemplify, historical mortality data from Sweden are interpreted in the light of the model. The decrease in mortality seen between cohorts born in 1905, compared to those born in 1885, can be accounted for by higher threshold to damage. This fits well with the many advances made in public health during the 20th century.

Cumulative damage model based on equivalent fatigue under multiaxial thermomechanical random loading

AbstractA new creep–fatigue damage cumulative model is proposed under multiaxial thermomechanical random loading, in which the damage at high temperature can be divided into the pure fatigue damage and the equivalent fatigue damage from creep. During the damage accumulation process, the elementary percentage of the equivalent fatigue damage increment is proportional to that of the creep damage increment, and the creep damage is converted to the equivalent fatigue damage. Moreover, combined with a multiaxial cyclic counting method, a life prediction method is developed based on the proposed creep–fatigue damage cumulative model. In the developed life prediction method, the effects of nonproportional hardening on the fatigue and creep damages are considered, and the influence of mean stress on damage is also taken into account. The thermomechanical fatigue experimental data for thin‐walled tubular specimen of superalloy GH4169 under multiaxial constant amplitude and variable amplitude loadings were used to verify the proposed model. The results showed that the proposed method can obtain satisfactory life prediction results.

The Metal Fatigue Failure Model under a Low- and High-Cycle Loading and Using the Temperature Effect

The models of damages accumulation in machinery structural components in the process of their complex loading in a high- and low-cycle area are considered. It is established that the damage accumulation process under these conditions is not subjected to the linear hypothesis. The necessity to take into account the simultaneous action of a complex of operational loads of different levels with the formation of a generalized block of forces is shown. The description of manufacturing some typical welded structures of components classified by the stress concentration level in a given loading pattern and their influence on endurance limits of such components is provided. The study results of fatigue damage accumulation processes according to temperature analogs of material endurance limits are presented. Equations approximating their S-N curves are obtained.

Defect evolution in Ni and solid-solution alloys of NiFe and NiFeCoCr under ion irradiation at 16 and 300 K

Single-phase concentrated solid-solution alloys (SP-CSAs) have shown unique chemical complexity at the levels of electrons and atoms, and their defect evolution is expected to be different from conventional dilute alloys. Single crystals of Ni, NiFe and NiFeCoCr are chosen as model systems to understand the chemical complexity on defect formation and damage accumulation in SP-CSAs under ion irradiation. The high-quality crystals were irradiated at 16 and 300 K to different ion fluences, to form irradiated region with little to heavy damages. The ion-induced damage was determined using Rutherford backscattering spectrometry technique along a channeling direction (RBS/C) and the level of lattice damage in irradiated Ni and SP-CSAs was quantified from Monte Carlo (MC) simulations. The results are interpreted using the Multi Step Damage Accumulation model to reveal material damage accumulation kinetics. Key findings of the study are that in case of room temperature irradiations the damage level measured for complex alloys at the highest irradiation fluence of 2 × 1015 cm−2 (∼3 dpa) is significantly higher than that obtained for pure nickel samples and suggest two-step damage accumulation process with a defect transformation taking place at a fluence of about 1.5 × 1015 cm−2. Moreover, structural and damage kinetic differences clearly imply that, with increasing degree of chemical complexity and high solid-solution strengthening effects from Ni to NiFe and to NiFeCoCr, the enhanced lattice stiffness resists to randomization of atomic configurations and inhibits the growth of extended defects.

Study on Material Damage of Carbide Tool during Heavy-Duty Cutting

With the rapid development of heavy-duty cutting, carbide tool damage has gradually become an important research direction. At present, most researches on tool damage are limited to macroscopic aspects, and there is still a lack of depth in exploring the essential mechanism of the microscopic. In heavy cutting process, the failure mechanism of carbide tool is the gradual process of damage accumulation, crack initiation, crack propagation and tool breakage. Based on the tool failure experiment of heavy cutting and the damage theory, the damage problem of carbide tool material is studied. Firstly, the damage conditions formed by the external load environment and the internal structure of the tool material are discussed. Then the damage phenomenon of the cemented carbide tool, the formation and evolution of damage crack are analyzed. The problem of tool damage is studied by combining finite element analysis. According to Hopkinson experiment, the stress-strain relationship of carbide material is analyzed. Finally, the influence of temperature on material damage is analyzed through high temperature experiment of carbide material, and the damage variable is characterized by different parameters. The above research can not only improves the specific process of tool breakage in heavy cutting process, but also provides a theoretical basis for the study of tool breakage mechanism.

Interaction of radiation-induced defects with tungsten grain boundaries at across scales: a short review

As promising candidates for plasma-facing materials, tungsten-based materials suffer the irradiation of high-energy neutrons in addition to the hydrogen isotopes and helium irradiation and the high-thermal flux. Radiation-produced defects, e.g. self-interstitial atoms (SIAs) and vacancies (Vs), can induce the hardening and embrittlement of tungsten, meanwhile enhancing the retention of hydrogen isotopes and helium in tungsten. Reducing the grain size of materials to introduce a high density of defect sinks, e.g., grain boundaries (GBs) prevalent in nano-/ultrafine-crystalline materials, was demonstrated to be an effective approach for mitigating irradiation damage in tungsten. In this paper, we reviewed the theoretical advances in exploring radiation-resistance of nano-structured tungsten at across scales. It was concentrated on the results of molecular dynamics, molecular statics, and the object kinetic Monte Carlo simulations on the fundamental interaction of the radiation-created Vs and SIAs with the GB. These mechanisms include GB-promoted V/SIA migration and SIA-V recombination, interstitial-emission induced annihilation, coupling of the V migration close to the GB with the SIA motion within the GB, and interstitial reflection by the locally dense GB structure. We proposed the remaining scientific issues on the defect-GB interactions at across scales and their relation to experimental observations. We prospected the possible trends for simulating the radiation damage accumulation and healing processes in nano-structured tungsten in terms of the development of the across-scale computational techniques and efficiency of the GB-enhanced tolerance of tungsten to irradiation under complex in-service conditions.

Damage accumulation mechanism in PIN diode limiters induced via multiple microwave pulses

Positive-intrinsic-negative (PIN) diodes are widely used as limiters to protect sensitive components from damage in radio frequency (RF) receiver systems and communication front-ends. However, PIN diode limiters can be burnt out due to the microwave pulses coupling through the front-end of RF receiver systems. The damage processes and mechanisms in PIN limiters are undoubtedly important topics. Here, the damage accumulation process in PIN limiters induced by external microwave pulses is studied via the injection experiments. The relationship between the degree of damage (i.e., insertion loss) in the limiters and number of the injected pulses is reported. The maximum temperature criterion for burnout in PIN limiters is theoretically predicted and experimentally verified not accurate, and it is further observed that the insertion loss of the PIN diode limiter changes significantly only if more energy is injected into the limiter via microwave pulses.

Low-cycle fatigue behavior of austenitic stainless steels with gradient structured surface layer

Low-cycle fatigue behavior of gradient structured (GSed) 316L steels is investigated. The results show that both the homogeneous and gradient structures exhibit first cyclic hardening then cyclic softening. The GSed surface layer can, however, speed up cyclic hardening and extend cyclic softening processes. The analyses using hysteresis energy-based criterion indicates that the former phenomenon can be attributed to the reduced fatigue damage capacity, while the latter to the improved ability of damage defusing. This finding accordingly pinpoints that the retarded fatigue damage accumulation process has been acting as the main contributor to the enhanced fatigue performance of GSed 316L steels.

Real-time quantification of fresh and hardened mechanical property for 3D printing material by intellectualization with piezoelectric transducers

This study is a pilot exploration to develop rigorous, green, intellectualized approach for optimal controlling the 3D concrete printing. The mechanical performances of 3D printed samples during super-early age, early age, and hardened state are tested and monitored using piezoelectric zirconate titanate (PZT) patches. EMI sensing technique is applied to quantify stiffness gain of printed concrete to evaluate the structural build-up behaviour by establishing the instant correlation between the stiffness of concrete and the EMI signatures. An optimization method for printing process based on EMI detection is proposed. In this way, the PZT signals can be feedback to the digital control system of printer in real time to adjust the printing setting. Instant intellectualization for the 3D printing technique is then realized and the buildability of the printed concrete is expected to be improved. The different early age properties of both printed and casted composites are elaborated. Thereafter, changes of frequency and amplitude in the conductance spectrum acquired by mounted PZT patches are employed to characterize and quantify the mechanical behaviours of the 3D printed samples exposed to orthogonal loadings, which contribute to the understanding of damage accumulation and failure process of concrete materials.

ЧИСЛЕННОЕ МОДЕЛИРОВАНИЕ УСТАЛОСТНОЙ ДОЛГОВЕЧНОСТИ ЭЛЕМЕНТОВ КОНСТРУКЦИЙ ПРИ ТЕРМОЦИКЛИЧЕСКОМ НАГРУЖЕНИИ

The paper considers processes of fatigue life of materials and structures in the exploitation conditions characterized by multiparametric nonstationary thermal-mechanical effects In the framework of mechanics of damaged media, a mathematical model is developed that describes processes of thermal-plastic deformation and fatigue damage accumulation in materials with degradation according to low- and high-cycle fatigue mechanisms (accounting for their interaction). The model consists of three interconnected parts: relations determining cyclic thermal-plastic behavior of a material, accounting for its dependence on the failure process; equations describing kinetics of fatigue damage accumulation; a strength criterion of the damaged material. The version of the defining relations of thermal plasticity is based on the notion of the yield surface and the principle of orthogonality of the plastic strain rate vector to the yield surface at the loading point and reflects the main effects of the process of cyclic plastic deformation of the material for arbitrarily complex trajectories of combined thermal-mechanical loading. The version of kinetic equations of fatigue damage accumulation is based on introducing a scalar parameter of damage degree and on energy-based principles, and takes into account the main effects of the nucleation, growth and merging of microdefects under arbitrarily complex loading regimes. A generalized form of an evolutionary equation of fatigue damage accumulation in low-cycle and high-cycle fatigue regions is introduced. The condition when the damage degree reaches its critical value is taken as the strength criterion of the damaged material. To assess the reliability and the scope of applicability of the developed defining relations of mechanics of damaged media, processes of thermal-plastic deformation and fatigue damage accumulation have been numerically analyzed, and the numerical results obtained have been compared with the data of full-scale experiments for a particular applied problem. The effect of the dropping frequency of a distillate on thermal cyclic fatigue life of the material of a heated surface of a tube has been numerically analyzed. The computational results for the fatigue damage accumulation processes under thermal pulsed loading are compared with experimental data. It is shown that the developed model describes both qualitatively and, accurately enough for engineering purposes, quantitatively the experimental data and can be effectively used for evaluating thermal-cyclic fatigue life of structures working in the conditions of multiaxial non-proportional regimes of combined thermal-mechanical loading.

Mathematical Modeling of Failure and Deformation Processes in Metal Alloys and Composites

Based on experimental examples, the strength characteristics of metal alloys and composites under tensile and compressive loads are considered to demonstrate both their similarity and difference. Under tensile loads, their behavior is essentially the same. Under compressive loads, the composite shows different properties, but similar to the behavior of a metal alloy under tension. When tensioned and compressed, it fractured as a material with a different structure. When a metal alloy is cyclically compressed, the damage accumulation process is attenuated, which reduces the alloy longevity during subsequent tension. The analysis of experimental data for various types of loading from the standpoint of the kinetic concept of fracture is carried out. Instead of a number of incompatible approaches or a formal description of experimental data, that based on the theory of reaction rates is used. Mathematical modeling of processes is carried out using rheological models of the material. Structural models of the material, called physical media, reflect the thermodynamic processes of flow, failure, and changes in the structure of the material. Parametric identification of structural models is carried out on the basis of the minimum necessary basic experiment: loading of specimens with different speeds at several temperature values and by the amplitude dependence of inelasticity. Based on results of these experiments, the scope of applicability conditions for this material and test modes necessary for parametric identification of models are selected. One fracture criterion is used, which formally corresponds to the achievement of a threshold concentration of micro-damage in any volume of the material, leading to macro-fracture. The application of mathematical models for calculating the longevity of materials depending on the temperature and force loading conditions and the nature of their changes is shown. Calculations of longevity under constant, monotonously increasing and variable loads under conditions of constant or changing temperatures are based on the relationship of plastic flow and failure processes distributed over the volume of the material. They are performed numerically by time steps depending on the ratio of the rate of change of temperature and stresses.

Defining relations of mechanics of damaged media effected by fatigue and creep

A possible version of a model describing degradation of initial strength properties of structural alloys affected by fatigue and creep is introduced, based on the modern viewpoint of mechanics of damaged media (MDM). Processes of viscoplastic deformation and damager accumulation in structural alloys are analyzed using numerical modeling. Special attention is paid to the issues of modeling the processes of viscoplastic deformation and damage accumulation for complex deformation processes accompanied by the rotation of main sites of stress and strain tensors. New qualitative and quantitative features of the failure process are noted, which are connected with stressed-strained state history, damage degree, stress relaxation and other factors.

Numerical Investigation of Damage Accumulation and Failure Processes in Random Porous Bicontinuous Media

Heterogeneous materials with bicontinuous foam-like structure were investigated. The aim of the work was to create models of failure of representative volume elements (RVEs) of such materials and to reveal the dependencies of the character of failure processes on the structural morphology peculiarities. To create models of RVEs with open-cell interpenetrating structures, approaches based on the analytical determination of surfaces separating the two phases were used. Mechanical modeling was performed with the finite element analysis using properties degradation and element removal techniques. The modelling results obtained for high-dense aluminum foam materials are presented. The influence of the size of representative volume element and its volume fraction on the fracture process has been studied.