Low-Cycle Fatigue Crack Initiation Simulation and Life Prediction of Powder Superalloy Considering Inclusion-Matrix Interface Debonding

From the perspective of damage mechanics, the damage parameters were introduced as the characterizing quantity of the decrease in the mechanical properties of powder superalloy material FGH96 under fatigue loading. By deriving a damage evolution equation, a fatigue life prediction model of powder superalloy containing inclusions was constructed based on damage mechanics. The specimens containing elliptical subsurface inclusions and semielliptical surface inclusions were considered. The CONTA172 and TARGE169 elements of finite element software (ANSYS) were used to simulate the interfacial debonding between the inclusions and matrix, and the interface crack initiation life was calculated. Through finite element modeling, the stress field evolution during the interface debonding was traced by simulation. Finally, the effect of the position and shape size of inclusions on interface debonding was explored.

Acoustic Emission Study on the Damage Evolution of a Corroded Reinforced Concrete Column under Axial Loads

In this paper, the damage of a reinforced concrete (RC) column with various levels of reinforcement corrosion under axial loads is characterized using the acoustic emission (AE) technique. Based on the AE rate process theory, a modified damage evolution equation of RC associated with the axial load and different corrosion rates is proposed. The experimental results show that the measured AE signal parameters during the loading process are closely related to the damage evolution of the RC column as well as the reinforcement corrosion level. The proposed modified damage evolution equation enables dynamic analysis for the damage of corrosion on a RC column under axial loading for a further real-time quantitative evaluation of corrosion damage on reinforced concrete.

Microfracture development and chemical damage analysis of limestone based on fractal theory

To explore the influence of microfracture development caused by chemical dissolution on the mechanical properties of limestone, this paper presents a new numerical simulation and quantitative analysis method. First, the dissolution rate was determined by the theory of chemical kinetics, and a differential equation that can be solved for results of the fracture evolution process by COMSOL Multiphysics was established to describe the microfracture's expansion. The fractal dimensions of the microfractures were found to have a linear relationship with the damage variables at different time periods through analysis of the simulation results with the fractal geometry method using fracture width as the index, which proves that the evolution of damage has a fractal nature. After that, a damage evolution equation was fitted to predict the deterioration in rock mechanical properties under hydrochemical actions and the predictive uniaxial compressive strength of limestone is seen to be in agreement with experimental test results. The application of the fractal geometry method has important engineering significance as it relates the development of microscopic fractures to changes in the macroscopic mechanical properties and predicts the mechanical properties of the rock under chemical damage.

A new damage-coupled cyclic plastic model for whole-life ratchetting of heat-treated U75V steel

In the framework of continuum damage mechanics, a new damage-coupled cyclic plastic model is proposed to describe the nonlinear evolution of whole-life ratchetting and its dependence on the stress level. The characteristic that the damage evolution rate of U75V heat-treated steel decays in the initial load cycles is considered by introducing a modified term into classic damage evolution equation. A hybrid fatigue failure criterion considering both the fatigue and ratchetting strain-induced failures is established based on the fatigue failure rule concluded from experiments. Comparisons between simulated and experimental stress–strain hysteresis loops, ratchetting strains, damage evolutions, and fatigue lives are performed to validate the proposed model.

Surface Settlement Damage Model of Pile-Anchor Supporting Structure in Deep Excavation

In damage mechanics, the deep excavation of soil is a process of damage development, and soil failure can be considered a process of continuously transforming undisturbed soil to damaged soil. Therefore, this study considered the occurrence of soil damage during the pit excavation, established a soil damage model, damage evolution equation, and soil damage constitutive relationship, and then deduced a calculate model of the pile displacement under the consideration of soil damage. Based on the principle of the stratum loss method, the surface settlement around a deep excavated pit was assumed as a skewed distribution curve, and the surface settlement of the pile-anchor supporting pit was solved. Based on this established method, finite element analysis software was used to calculate the surface subsidence for a field case, and the numerical results were compared with monitoring data in the field. The results revealed that, to a certain extent, soil damage affected the distribution of surface settlement in excavated pits. With the development of soil damage, the mechanical properties of soil gradually decreased, which led to increased surface settlement and changes in the direction of the excavation pit. Because soil damage is an important factor causing surface settlement, it is meaningful to consider soil damage when calculating the surface settlement in the deep excavation of pits.

A continuum damage mechanics model for fatigue and degradation of fiber reinforced materials

Objective of the present study is the definition of a continuum damage mechanics material model describing the degradation of fiber reinforced materials under fatigue loads up to final failure. Based on the linear elastic framework, a brittle damage model for fatigue conditions is derived, where the damage constitutes the only nonlinearity. The model accounts for damage effects by successive degradation of the elastic moduli. Assuming that material damage is driven by microplastic work, a stress-driven damage evolution equation is defined. For generality, a fully three-dimensional formulation on single ply level is employed. The model is implemented into a finite element program. In a validation against experimental data on filament-wound carbon fiber reinforced material, the model proves to provide a good numerical approximation of the damage during the cyclic loading history up to final material failure.

Dynamic Constitutive Model Analysis of High Parameter Steel Fiber Reinforced Concrete

The traditional Holmquist-Johnson-Cook (HJC) constitutive model does not consider the effect of crack resistance, reinforcement and toughening effect of high parameter steel fiber on original concrete. The causes of the analysis effect of the high parameter reinforced concrete is not obvious. To address this problem, a dynamic constitutive model of high parameter steel fiber reinforced concrete is built in this paper. Based on the static constitutive model built by static force, a dynamic constitutive model is built based on the similarity between static and dynamic stress-strain curve. On this basis, the yield surface equation, state equation, and damage evolution equation of HJC constitutive model are constructed. An improved HJC constitutive model for high parameter steel fiber reinforced concrete is obtained by introducing the modification of the steel fiber reinforced, toughened, and strain rate effects into the HJC constitutive model. Dynamic analysis of high parameter steel fiber reinforced concrete is achieved by using the improved model. Experimental results show that the proposed model is effective in analyzing high parameter concrete and has strong applicability.

A continuum based macroscopic unified low-and high cycle fatigue model

In this work, an extension of a previously developed continuum based high-cycle fatigue model is enhanced to also capture the low-cycle fatigue regime, where significant plastic deformation of the bulk material takes place. Coupling of the LCFand HCF-models is due to the damage evolution equation. The high-cycle part of the model is based on the concepts of a moving endurance surface in the stress space with an associated evolving isotropic damage variable. Damage evolution in the low-cycle part is determined via plastic deformations and endurance function. For the plastic behaviour a non-linear isotropic and kinematic hardening J2-plasticity model is adopted. Within this unified approach, there is no need for heuristic cycle-counting approaches since the model is formulated by means of evolution equations, i.e. incremental relations, and not changes per cycle. Moreover, the model is inherently multiaxial and treats the uniaxial and multiaxial stress histories in the same manner. Calibration of the model parameters is discussed and results from some test cases are shown.

Study on micro-damage model of clay under tension

To improve the theoretical research on the tensile properties of soil, the damage model study was carried out in the present paper based on existing experimental results. In combination with the variation of the micro-structure of clay during the stretching process, the damage variable is defined by coupling the porosity with the pore distribution. According to the structure damage during the tensile process of clay under different initial conditions, the damage evolution equation is obtained and the damage model is established. At the same time, the applicability of the damage evolution equation and the damage model was verified by experimental data.

Constitutive Model and Damage Evolution of Mudstone under the Action of Dry-Wet Cycles

Mudstone is a natural type of geological material, which has different ways of mechanical response between natural state and dry-wet cycles. According to the complex damage theory of geological materials, rock masses can be considered as a composite material consisting of the structure phase and damage phase. The essence of the damage of rock masses is a damage evolution process, during which the deformation energy of the structure phase converts into dissipation energy of the damage phase, and the energy dissipation from phase transformation promotes the structure phase to change into the damage phase. In this study, a customized model test container and a novel test method are applied to study the decay rate of mudstone under different temperatures and over multiple dry-wet cycles. The decay rate and the damage variable are connected with each other and applied to the damage constitutive equation based on the energy principle to set up the damage evolution equation under the coupled action of dry-wet cycles and loads. Comparison of the proposed model with test results in a literature identifies the rationality of the established model and properly reflects the damage evolution of mudstone.