Symmetry Breakdown Related Fracture in 42CrMo4 Steel

Theoretical-Experimental failure analysis of the c-Al0.66Ti0.33N-M2 steel system using nanoindentation instrumented and finite element analysis

A theoretical-experimental methodology for failure analysis of the c-Al0.66Ti0.33N / Interface / M2 steel coating system is proposed here. This c-Al0.66Ti0.33N coating was deposited by the arc-PVD technique. For coating modeling the traction-separation law and the extended finite element method-XFEM were applied, the cohesive zones model was used for interface modeling and the Ramberg-Osgood law for substrate modeling. Experimental values using the instrumented nanoindentation technique, the scratch test and tensile stress test were obtained and introduced into the model. By means of nanoinden…

Avalanches in Breakdown and Fracture Processes

We investigate the breakdown of disordered networks under the action of an increasing external---mechanical or electrical---force. We perform a mean-field analysis and estimate scaling exponents for the approach to the instability. By simulating two-dimensional models of electric breakdown and fracture we observe that the breakdown is preceded by avalanche events. The avalanches can be described by scaling laws, and the estimated values of the exponents are consistent with those found in mean-field theory. The breakdown point is characterized by a discontinuity in the macroscopic properties of…

奥氏体钢中辐照诱发韧脆转变的原子尺度研究

Atomistic Study of Radiation-Induced Ductile-to-Brittle Transition in Austenitic Steel

本文通过分子动力学模拟研究辐照Fe-Ni-Cr合金的韧脆转变，揭示空洞促进裂纹扩展而位错环阻碍并偏转裂纹的机制，并将断裂能分解方法推广至辐照材料以量化表面能与塑性功的贡献。

Breakdown of Reye's theory in nanoscale wear

Building on an analogy to ductile fracture mechanics, we quantify the size of debris particles created during adhesive wear. Earlier work suggested a linear relation between tangential work and wear debris volume, assuming that the debris size is proportional to the micro contact size multiplied by the junction shear strength. However, the present study reveals deviations from linearity. These deviations can be rationalized with fracture mechanics and imply that less work is necessary to generate debris than what was assumed. Here, we postulate that the work needed to detach a wear particle is…

Mode II fracture of an MMA adhesive layer: theory versus experiment

Thick adhesive layers have potential structural application in ship construction for the joining of a composite superstructure to a steel hull. The purpose of this study is to develop a mechanics model for the adhesive fracture of such lap joints under shear loading. Modified Thick-Adherend-Shear-Test (TAST) specimens made from a MMA-based adhesive and steel adherents are designed and fabricated. Crack initiation and growth of these joints is measured and monitored by Digital Image Correlation (DIC). An attempt is made to use a cohesive zone model to predict the magnitude of shear strain acros…

揭示增材制造钢中裂纹萌生的潜在机制

Unravelling the mechanisms underlying crack initiation in additively manufactured steel

研究增材制造钢裂纹萌生机制，结合多模态技术观察裂纹尖端塑性三维演变，发现锻造钢与增材制造合金在裂纹尖端塑性表现不同，揭示抗断裂能力受其空间演变控制，为提高损伤容限提供机理框架。

Carbon in solution and the Charpy impact performance of medium Mn steels

Carbon is a well known austenite stabiliser and can be used to alter the stacking fault energy and stability against martensitic transformation in medium Mn steels, producing a range of deformation mechanisms such as the Transformation Induced Plasticity (TRIP) or combined Twinning and Transformation Induced Plasticity (TWIP $+$ TRIP) effects. However, the effect of C beyond quasi-static tensile behaviour is less well known. Therefore, two medium Mn steels with 0.2 wt\% and 0.5 wt\% C were designed to produce similar austenite fractions and stability and therefore tensile behaviour. These were…

Statistical Mechanics of Cracks: Thermodynamic Limit, Fluctuations, Breakdown, and Asymptotics of Elastic Theory

We study a class of models for brittle fracture: elastic theory models which allow for cracks but not for plastic flow. We show that these models exhibit, at all finite temperatures, a transition to fracture under applied load similar to that at a first order liquid-gas transition. We study this transition at low temperature for small tension. We discuss the appropriate thermodynamic limit of these theories: a large class of boundary conditions is identified for which the energy release for a crack becomes independent of the macroscopic shape of the material. Using the complex variable method …

Elastic Composite, Reinforced Lightweight Concrete as a Type of Resilient Composite Systems

. A kind of "Elastic Composite, Reinforced Lightweight Concrete (ECRLC)" with the mentioned specifics is a type of "Resilient Composite Systems (RCS)" in which, contrary to the basic geometrical assumption of flexure theory in Solid Mechanics, "the strain changes in the beam height during bending" is typically "Non-linear". . Through employing this integrated structure, with significant high strain capability and modulus of resilience in bending, we could constructively achieve high bearing capacities in beams with secure fracture pattern, in less weight. . Due to the system particulars and it…

Breakdown of fiber bundles with stochastic load-redistribution

We study fracture processes within a stochastic fiber-bundle model where it is assumed that after the failure of a fiber, each intact fiber obtains a random fraction of the failing load. Within a Markov approximation, the breakdown properties of this model can be reduced to the solution of an integral equation. As examples we consider two different versions of this model that both can interpolate between global and local load redistribution. For the strength thresholds of the individual fibers, we consider a Weibull distribution and a uniform distribution, both truncated below a given initial …

Scaling for the Coalescence of Microfractures before Breakdown

We study the behavior of fracture in disordered systems close to the breakdown point. We simulate numerically both scalar (resistor network) and vectorial (spring network) models with threshold disorder, driven at constant current and stress rate respectively. We analyze the scaling of the susceptibility and the cluster size close to the breakdown. We observe avalanche behavior and clustering of the cracks. We find that the scaling exponents are consistent with those found close to a mean-field spinodal and present analogies between the coalescence of microfractures and the coalescence of drop…

Time dependence of breakdown in a global fiber-bundle model with continuous damage

A time-dependent global fiber-bundle model of fracture with continuous damage is formulated in terms of a set of coupled non-linear differential equations. A first integral of this set is analytically obtained. The time evolution of the system is studied by applying a discrete probabilistic method. Several results are discussed emphasizing their differences with the standard time-dependent model. The results obtained show that with this simple model a variety of experimental observations can be qualitatively reproduced.