Mathematical Modeling of the Processes of Deformation of Soils with Time

It has been suggested that the rheological properties of soils be modeled by the integral Volterra equation of the second kind of the nonlinear heredity theory and by the differential equation which, under certain conditions, approximately replaces the adopted integral equation. Parameters of these governing equations have been found from experimental data for a number of soils. The processes of creep of soils have been studied.     

Mathematical Modeling of Thermomechanical Processes under Intense Thermal Effect

Mathematical models of thermomechanical processes which are based on the laws of rational thermodynamics of irreversible processes are treated. Singular features of the unsteady-state behavior of a continuous medium are demonstrated within different models, such as a medium with internal parameters of state, a medium with memory, and a medium of the velocity type.     

Experimental Assessment and Micromechanical Modeling of Additively Manufactured Austenitic Steels under Cyclic Loading

The present work deals with the cyclic deformation behavior of additively manufactured austenitic stainless steel 316L. Since fatigue experiments are complex and time-consuming, it is important to develop accurate numerical models to predict cyclic plastic deformation and extrapolate the limited experimental results into a wider range of conditions, considering also the microstructures obtained by additive manufacturing. Herein, specimens of 316L steel are produced by powder bed fusion of metals with laser beams (PBF-LB/M) with different parameters, and cyclic strain tests are performed to assess their deformation behavior under cyclic loads at room temperature. Additionally, a micromechanical model is set up, based on representative volume elements (RVE) mimicking the microstructure of the experimentally tested material that is characterized by electron backscatter diffraction (EBSD) analysis. With the help of these RVEs, the deformation-dependent internal stresses within the microstructure can be simulated in a realistic manner. The additively manufactured specimens are produced with their loading axis either parallel or perpendicular to the building direction, and the resulting anisotropic behavior under cyclic straining is investigated. Results highlight significant effects of specimen orientation and crystallographic texture and only a minor influence of grain shape on cyclic behavior.     

Edge-Cracks in Single Crystals Under Monotonic and Cyclic Loads

Basic solutions are obtained for edge-cracks lying along the primary slip plane in a single crystal. The study is motivated by Stage I fatigue crack growth wherein crack orientation is controlled by the slip direction and continued growth is dependent on the crack overcoming barriers to slip. Plasticity is assumed to occur as slip along planes inclined at 45^ to the surface. Problems where slip is limited to persistent slip bands are considered side-by-side with the problem where slip is not confined. Results for both monotonic and cyclic loadings are presented, with emphasis on the crack tip opening and sliding displacements. Both small and large scale yielding are considered. Preliminary results are given for interaction with barriers to slip, such as a grain boundary. This revised version was published online in July 2006 with corrections to the Cover Date.     

Cyclic Behavior and Damage Analysis of Brass under Cyclic Torsional Loading

Fatigue behavior of brass was studied at a constant deformation rate of 5.6 × 10⁻³ s⁻¹ to understand the cyclic behavior and fatigue life under cyclic torsional deformation. Strains were in the range of 0.35 to 4.2%. In the as-drawn condition, it was found that the cyclic hardening/softening behavior strongly depends on the strain amplitude. For low strain amplitude, cyclic saturation occurred after an initial cyclic hardening stage, but for high strain amplitude, saturation could not be reached. Cyclic stress-strain (CSS) curve showed the presence of three distinct regions with a short quasi-plateau region in the intermediate amplitude range. Quantitative fatigue damage was assessed by microscopic observations of surface cracks.     

Monotonic and Cyclic Deformations of Case‐Hardened Steels Including Residual Stress Effects

Abstract: Monotonic and cyclic deformations of case‐hardened steel specimens under axial loading were investigated experimentally and analytically. A finite element (FE) model for the case‐hardened specimens was constructed to study multiaxial stresses due to different plastic flow behaviour between the case and the core, as well as to evaluate residual stress relaxation and redistribution subsequent to cyclic loading. The multiaxial stress is shown to increase the effective stress on the surface, and, therefore, unfavourable to yielding or fatigue crack nucleation. The residual stresses are shown to relax or redistribute, even in the elastic‐behaving region, when any part of a case‐hardened specimen or component undergoes plastic deformation. Multi‐layer models were used to analyse and predict monotonic and cyclic deformation behaviours of the case‐hardened specimen based on the core and case material properties, and the results are compared with the experimental as well as FE model results. The predicted monotonic stress–strain curves were close to the experimental curves, but the predicted cyclic stress–strain curves were higher than the experimental curves.     

Modeling Strength Degradation of Fiber-Reinforced Ceramic-Matrix Composites Subjected to Cyclic Loading at Elevated Temperatures in Oxidative Environments

In this paper, the strength degradation of non-oxide and oxide/oxide fiber-reinforced ceramic-matrix composites (CMCs) subjected to cyclic loading at elevated temperatures in oxidative environments has been investigated. Considering damage mechanisms of matrix cracking, interface debonding, interface wear, interface oxidation and fibers fracture, the composite residual strength model has been established by combining the micro stress field of the damaged composites, the damage models, and the fracture criterion. The relationships between the composite residual strength, fatigue peak stress, interface debonding, fibers failure and cycle number have been established. The effects of peak stress level, initial and steady-state interface shear stress, fiber Weibull modulus and fiber strength, and testing temperature on the degradation of composite strength and fibers failure have been investigated. The evolution of residual strength versus cycle number curves of non-oxide and oxide/oxide CMCs under cyclic loading at elevated temperatures in oxidative environments have been predicted.     

Investigation into Z-Pin Reinforced Composite Skin/Stiffener Debond under Monotonic and Cyclic Bending

Skin/stiffener debonding has been a longstanding concern for the users of stiffened composite panels in long-term service. Z-pinning technology is an emerging solution to reinforce the composite assembly joints. This work experimentally characterizes the progressive debonding of Z-pinned skin/stiffener interface with the skin under static bend loading. The three-stage failure process is identified as: flange edge debonding, pin/laminate debonding, and ultimate structural failure. Three different distribution patterns were compared in terms of the static debonding properties revealed the affirmative fact that locating pins in high normal stress regions, that is close to the flange edges in skin/stiffener structures, is more beneficial to utilize the full potential of Z-pinning reinforcement. The unit strip FE model was developed and demonstrated effective to analysis the effect of Z-pin distribution on the ultimate debond load. On the other hand, the evolution of fatigue cracks at Z-pinned skin/flange interface was investigated with a series of displacement-controlled fatigue bending tests and microscopic observations. Results show that Z-pinning postpones crack initiations at low displacement levels, and the remarkable crack-arresting function of pins enables the structure a prolonged fatigue life. However, pins become less effective when the maximum displacement exceeds the crack initiation level due to gradually pullout of pins.     

Plasticity of Additionally Hardened Materials under Cyclic Loading

Strength of Materials - Mathematical simulation of elastoplastic deformation of additionally isotropically hardened materials under proportional and nonproportional cyclic loadings is examined. A...     

Kinetics of Fatigue Cracks under Cyclic Thermomechanical Loading

We describe some results of investigations into processes accompanying the growth of fatigue cracks under cyclic thermal and thermomechanical loading of structural elements made of heat-resistant alloys. On the basis of experimental data on the kinetics of damage of materials and the results of numerical simulation of their thermostressed state under loads reproducing service conditions, we analyze the conditions of propagation of fatigue cracks by using methods of fracture mechanics. In addition, we present recommendations concerning the evaluation of the endurance of structural elements like blades of gas-turbine units.     

Modeling the Loading and Unloading of Drugs into Nanotubes

One of the most promising applications of nanotechnology is that of drug delivery, and in particular the targeted delivery of drugs using nanotubes. Functionalized nanotubes might be able to target specific cells, become ingested, and then release their contents in response to a chemical trigger. This will have significant implications for the future treatment of patients, particularly those suffering from cancer, for whom presently the nonspecific nature of chemotherapy often kills healthy normal cells. Research to date has largely been through experiments investigating toxicity, biocompatibility, solubility, functionalization, and cellular uptake. More recently, the loading and unloading of molecular cargo has gained momentum from both experimental and theoretical investigations. This Review focuses on the loading and unloading of molecular cargo and highlights recent theoretical investigations, which to date have received very little attention in the review literature. The development of nanotube drug‐delivery capsules is of vital concern for the improvement of medical treatment, and mathematical modeling tends to facilitate such development and provides a quicker route to applications of the technology. This Review highlights the latest progress in terms of theoretical investigations and provides a focus for the development of the next generation of medical therapeutics.

     

Failure of Magnesium Sheets Under Monotonic Loading: 3D Examination of Fracture Mode and Mechanisms

Damage evolution in a commercial magnesium sheet alloy (Mg-3Al-1Zn-0.3Mn) at room temperature is investigated. Kahn tear tests were performed to characterize the crack extension behaviour. Scanning electron microscopy of the fracture surfaces revealed flat inclined areas and the absence of cracked particles and dimples. Post-mortem synchrotron tomography of a stopped crack was used to further identify the predominant damage mechanism in the specimen’s ligament. Nucleation of submicrometre-voids, a micro-void sheeting mechanism and the absence of classical void growth could be identified.     

Crack-Tip Stress-Strain Fields During Cyclic Loading and Effect of Overload

Finite-deformation elastoplastic analysis of a plane-strain crack subjected to mode I cyclic loading under small scale yielding was performed. The influence of the load range, load ratio and overload on the crack tip stress-strain field is presented. Two independent parameters of cyclic loading, such as ΔK and K _max, both substantially affect the near tip evolutions of cyclic stresses and plastic strains, in agreement with typical experimental trends of fatigue cracking. This implies that the behaviour of cracks is governed by stress and strain fields ahead of the tip, via their control over the key process variables (damage accumulation and rupture, i.e., bond-breaking), so that the coupled process becomes a two-parameter one in terms of fracture mechanics variables ΔK and K _max.     

Numerical Modeling of Casting Processes

Recent progress on work related to numerical modeling of casting processes at the Industrial Materials Institute (IMI) is presented. Depending on the type of casting process involved, two different modeling approaches are used. The first, applied to simulate laminar or turbulent flow in the cavity of thin wall castings, is based on a 2D shell element model. This has the advantage of being computationally efficient from the CPU standpoint while, at the same time, provides a reasonably accurate solution to the problem. In the second approach, a 3D finite element method is used for parts that are thick (such as in low pressure or gravity casting), or where the problem is associated with both the part and mold (such as in heat transfer calculations). Whatever the technique chosen, in performing numerical modeling, the foundry hopes to use the results to optimize die and part design, as well as to reduce manufacturing costs. By being able to predict filing, solidification, stresses and shrinkage, a good idea of product quality and performance can often be obtained at the initial stage of the product development cycle.Examples of simulations conducted using an experimental die, an automotive housing and a wheel in an aluminum alloy are given.     

In-situ SEM Observation of Monotonic and Cyclic Deformed Structure in Ti-2Al-2.5Zr Alloy

The SEM observation in situ of monotonic and cyclic deformed structure in Ti-2Al-2.5Zr alloy was performed. The regularity of slippage, crack nucleation, propagation and the typical dislocation configuration were also investigated. The twin and twist play an important role in maintaining homogeneous deformation in the final plastic deformation stage.