Stress Distribution In Materials Research Articles

Numerical analysis of flexural behaviour of UHPC-CFTS columns as enclosure supports for electrical substations

Abstract This study establishes a finite element analysis model of ultra-high-performance concrete (UHPC) encased concrete filled steel tube (CFST) composite columns under combined compression and bending. Appropriate constitutive models and element types are selected as the basis. The finite element model simulates the test results of steel-concrete composite columns, and the applicability of the model is verified by comparison with existing test data of UHPC encased CFSTs. On the basis of demonstrating model reliability, the full-range load-deformation curves of UHPC encased CFSTs with different concrete strengths under compression-bending are compared. The failure modes and material stress distributions are analyzed to elucidate the influence mechanism of the UHPC on the flexural performance of UHPC encased CFSTs under combined compression and bending. The results show that compared to normal concrete, UHPC can effectively improve the flexural capacity of UHPC encased CFST columns. Owing to the addition of steel fibers, the failure mode of UHPC encased CFSTs under combined compression and bending is more integral compared to normal concrete. The research results of this study can provide references for the performance evaluation and design of UHPC encased CFSTs in the structural enclosures for electrical equipment in high/low voltage substations.

Constructing stress-release layer on Si nanoparticles for high-performance lithium storage

Tailing structures of silicon anode to alleviate the mechanical stress has an important significance in the development of lithium-ion batteries (LIBs). Herein, the stress-released layer of N-doped cubic carbon on the surface of Si nanoparticles (Si@NCC) is explored to stabilize the electrode. Endowed with the unique superiority, the Si@NCC electrode delivers an impressive lithium storage performance with high specific capacity of 630 mAh/g at 0.1 A/g, excellent cycling stability (72.0 % capacity retention after 100 cycles at 0.1 A/g) and good rate capability (375 mAh/g at 2 A/g). It has been demonstrated that the N-doped cubic carbon shell with high conductivity can effectively limit the expansion and agglomeration of Si nanoparticles. Besides, the COMSOL simulations of the stress distributions in materials confirm that the N-doped cubic carbon layer could remarkably decrease the stress originated from the volume expansion of Si nanoparticles during the lithiation. Therefore, this work provides ideas for the mechanical effect of Si-based anodes for lithium storage and sheds lights on the designing advanced materials toward high-performance energy storage devices.

Making stress visible: A method to quantify local stress distribution in metals using digital image correlation method

Stress (force) induces the deformation of materials. Stress distribution in materials is generally heterogeneous depending on their shapes and microstructures, which governs their global deformation and failure, and sometimes stress concentration induces serious incidents in society. However, it has been challenging to experimentally quantify stress distributions in materials in macro- and micro-scales by now. Here, we newly propose and establish a simple but promising method to quantify local stress distributions in materials by applying the digital image correlation (DIC) technique, which is applicable to all length scales. We expect that the newly developed method would become the first step to give an impact on fundamentally understanding the deformation and fracture of materials in various scales as well as on practically reducing risks in structural components.

High-Speed Stress Field Measurement In A Soft Substrate During Droplet Impact

In this study, we utilized high-speed photoelastic tomography to quantify dynamic stress fields within a soft substrate during droplet impact. This manuscript details the measurement technique, which employs a high-speed polarization camera and the principles of photoelastic tomography. Our method successfully enabled the quantitative measurement of dynamic stress fields in a soft substrate during droplet impact. Additionally, we conducted an analysis of the impact force derived through the spatial integration of the measured stress field. The discussion explored the interplay between the maximum impact force, droplet viscosity, and substrate elasticity. Our findings indicate that the maximum impact force 𝐹max can be expressed as a function with a self-similar variable of 𝑅𝑒 / 𝐶𝑎^2 , where 𝑅𝑒 is Reynolds number representing the droplet inertial force and droplet viscous force and 𝐶𝑎 is Cauchy number representing the ratio of the droplet inertial force and substrate elastic force. This combination, 𝑅𝑒 / 𝐶𝑎^2 , represents the relationship between the relaxation time of droplet and substrate deformation ( 𝜂/ 𝐸), the contact time of the droplet (𝑅 / 𝑉), and the ratio of substrate elastic force to droplet inertial force. Consequently, the maximum impact force 𝑅𝑒 / 𝐶𝑎^2 is determined by the balance between the relaxation and contact times. We believe that our developed method will significantly enhance the understanding of droplet impact phenomena. Furthermore, it holds potential for broader applications in various engineering processes, such as analyzing stress distribution in materials caused by liquid jet impact and studying cavitation bubbles in viscoelastic materials. This method's ability to provide detailed quantitative measurements of dynamic stress fields offers a valuable tool for future research and technological advancements in related fields.

Thermomechanical-induced cracking model for ceramic matrix composite laminates subjected to thermal gradients and transients

Regarding the potential damage and failure issues that may occur in high-temperature transient environments during the service process of ceramic matrix composite laminates, the present work proposes a multi-layer thermomechanical induced crack initiation model for ceramic matrix composite laminates subjected to thermal gradients and transients. This model can determine the history of temperature, deformation, and stress distribution within each layer of the material, as well as the steady-state energy release rate of all possible crack locations. Then the influence of bending constraints on material stress distribution and energy release rate is investigated, finding that maximum stress and energy release rate values are significantly lower without bending constraints compared to those under bending constraints. Furthermore, the study explores the impact of material structural parameters and boundary conditions on the energy release rate of ceramic matrix composite laminates, providing direct insights for designing laboratory tests and evaluating the lifespan of these materials under in-service conditions.

Spatial Constitutive Modeling of AA7050-T7451 with Anisotropic Stress Transformation.

The mechanical properties of anisotropic materials are generally characterized based on the orthotropy or transverse isotropy. However, the two-dimensional plane stress problems cannot comprehensively characterize the anisotropy of materials. In this study, based on the theory of elasticity and the transformation of the three-dimensional space coordinate system, combined with the projection relationship of the Cauchy stress tensor of an arbitrary section, the transformation relationship of the elastic modulus, shear modulus, and stress–strain between the orthogonal and load coordinate systems are obtained. The orthotropic Johnson-Cook (JC) constitutive model of AA7050-T7451 aluminum alloy is modified by fitting, and the constitutive relationship at any spatial angle is theoretically calculated by combining the obtained spatial coordinate transformation matrix. The generated spatial constitutive model is verified and modified through experiments. The results demonstrate that the theoretical mechanical properties and the modified spatial constitutive model can accurately reflect the effect of the spatial angle on the material stress distribution.

Effect of Transversely Isotropic Elasticity on Elastohydrodynamic Lubrication of Point Contacts.

Fiber-reinforced materials or 3D printed parts feature transversely isotropic elasticity. Although its influence on pressures, shapes, and sizes has been studied extensively for dry contacts, the transferability to lubricated contacts is fragmented. This numerical study investigates how the content and orientation of short fibers in fiber-reinforced polymers (FRP) affect elastohydrodynamic lubrication (EHL) of point contacts. Material properties are modeled with Tandon-Weng homogenization. For EHL modeling, a fully-coupled approach based on finite element discretization is used. Results on hydrodynamic pressure and film thickness as well as material stress distribution are analyzed and compared to common approximations using the effective contact moduli. It is shown that the combination of fiber content and orientation defines the effective contact stiffness that determines the contact shape, size, and film thickness. Furthermore, the contact regime can change if a contact-specific stiffness threshold is reached.

Material removal mechanism and penetration depth modeling of CF/PEEK composites under nano-scratching

In order to investigate the material removal mechanism of carbon fiber-reinforced thermoplastics (CFRTP), nanoscratching experiments of carbon fiber-reinforced polyetheretherketone (CF/PEEK), as a typical kind of thermoplastic composite, were performed along various feed directions of the indenter and fiber orientations. Material removal mechanism was researched based on surface and subsurface morphological features. Experimental results indicated that chips were easily attached to the sample surface and difficult to remove, while chips containing much resin tended to accumulate and were tough to break. In addition, under the radial load, it was often observed that the interface remained still well, even though the breaking occurred inside the fibers during the scratching process. And under the axial load, there was crack deflection near the resin which inhibited the cracks expansion between the fibers. Furthermore, a penetration depth modeling to the normal load for CF/PEEK nanoscratching was developed, taking into account the impacts of elastic recovery, anisotropy, heterogeneity and stress distribution of material. Experimental validations showed that the prediction results evaluated by theoretical model was close to the actual results.

A Review on Effect of Stress and Strain Distribution on the AA5083 With Respect to Different Channel Angle of ECAP

The focus of this study was on the effect of channel angle on stress distribution in the material aluminum alloy 5083. The mechanical properties of a mate- rial are related to the grain size. Equal channel angular pressing (ECAP) is a method for deforming materials in such a way that a strong mechanical prop- erties material is formed while the dimensions of the work piece stay fixed in order to make ultra-fine-grained materials. One of the parameters of ECAP is the channel angle. It’s crucial to understand the impact of a die channel angle on material stress distribution before designing one. When the work piece passes through the channel angle, the die channel angle is built differently to see the effect of stress distribution. At the place where the die’s channels angle intersected, the grain structure was evaluated. The result of the influence of die channel angle on stress distribution is shown in this study’s analysis. It is well established that the channel angle has an impact on mechanical behaviour. The inhomogeneity index (Ci)and standard deviation (S.D.) are two approaches for assessing strain homogeneity. Ciis demonstrated to be an ineffective tool for analysing strain distribution homogeneity. Furthermore, it is advised that constructing Equal Channel Angular Pressing die geometry to obtain the best strain circulation homogeneity rather also the best efficient strain consequence is preferable.

Investigations on cold-forming effect of cold-drawn duplex stainless steel tubular sections

The cold-drawing process is currently a significant way of manufacturing cold-formed structural tubular sections at room temperature. Furthermore, cold-drawing is more suitable for forming thick-walled sections with large dimensions than cold-rolling. Plastic deformation experienced during section forming causes increases in the mechanical properties and it also induces residual stresses in the cold-formed cross sections. This paper experimentally examined residual and material stress distributions in two types of cold-drawn tubular sections - three Circular Hollow Sections (CHS) and three Square Hollow Sections (SHS), and material-duplex (S22053) stainless steel. Based on the experimental findings, strength enhancement in CHS was not obvious owing to annealing treatment, removing cold work and increasing ductility. In this case, transverse bending residual stresses in CHS were only considered due to cold-forming effect. The residual stress distribution patterns including longitudinal and transverse stresses and predictive models for enhanced strength of the flat face of cold-drawn duplex stainless steel square hollow sections were developed. Comparisons of the predictions and the test data show that the proposed models were in good accuracy.

Numerical study of microstructural effects on chip formation in high speed cutting of ductile iron with discrete element method

Microstructural deformation and fracture process is important for chip formation and finished surface quality during metal cutting. In this paper, discrete element method (DEM) is introduced to establish a heterogeneous material model for cutting simulation to understand the microstructural deformation and fracture behaviors. A typical heterogeneous engineering material, ISO 450-10 ductile iron, was selected for modeling and experiments. Graphite nodules and ferrite grains were modeled respectively for studying their deformation behaviors. Cutting force and chip morphology obtained by simulation were compared with the experimental results. It shows that lamellar structure and unequal segments form at the chip free surface, which was also observed by optical microscope (OM) and scanning electron microscopy (SEM). The deformed degree of graphite nodules is much higher than that of ferrite grains. In addition, cracks are prone to produce and the chip size becomes smaller as the cutting speed increases. The velocity field and stress distribution of material near the rake face were investigated and the relationship between stress and cutting speed was further discussed. The velocity fluctuation of discrete particles in heterogeneous model is more obvious due to the microstructures compared with that in homogeneous model. Furthermore, the stress of material changes significantly with the increase of cutting speed since velocity vortexes may occur, resulting in the occurrence of the fracture. The results demonstrate that the influences of microstructure on crack initiation and chip formation are more significant at high cutting speeds.

T-scaling method for stress distribution scaling under small-scale yielding and its application to the prediction of fracture toughness temperature dependence

In this paper, a new method for scaling the crack-tip stress distribution under small-scale yielding conditions is proposed and named the T-scaling method. This method enables identification of the different stress distributions for materials with different tensile properties but identical load in terms of K or J. Then, by assuming that the temperature dependence of a material is represented by the stress-strain relationship temperature dependence, a method to predict the fracture load at an arbitrary temperature from the already known fracture load at a reference temperature is proposed. This method is combined with the T-scaling method and the knowledge that the “fracture stress for slip induced cleavage fracture is temperature independent.” Once the fracture load is assumed, the fracture toughness Jc at the temperature under consideration can be evaluated by running elastic-plastic finite element analysis. Finally, the above-mentioned framework for predicting the Jc temperature dependence of a material in the ductile-to-brittle temperature region was validated for 0.55% carbon steel JIS S55C and reactor pressure vessel steel A533B. The proposed framework seems to be able to solve the problem faced by the master curve in the relatively high temperature region by requiring only tensile tests.

小規模降伏条件下応力分布スケーリング法の提案と破壊靭性値の温度依存性予測への適用

In this paper, a new method for scaling the crack tip stress distribution under small scale yielding condition was proposed and named as T-scaling method. This method enables to identify the different stress distributions for materials with different tensile properties but identical load in terms of K or J. Then by assuming that the temperature dependence of a material is represented as the stress-strain relationship temperature dependence, a method to predict the fracture load at an arbitrary temperature from the already known fracture load at a reference temperature was proposed. This method combined the T-scaling method and the knowledge “fracture stress for slip induced cleavage fracture is temperature independent.” Once the fracture load is predicted, fracture toughness Jc at the temperature under consideration can be evaluated by running elastic-plastic finite element analysis. Finally, the above-mentioned framework to predict the Jc temperature dependency of a material in the ductile-to-brittle temperature distribution was validated for 0.55% carbon steel JIS S55C. The proposed framework seems to have a possibility to solve the problem the master curve is facing in the relatively higher temperature region, by requiring only tensile tests.

Defect-Tolerant Bioinspired Hierarchical Composites: Simulation and Experiment.

Defect tolerance, the capacity of a material to maintain strength even under the presence of cracks or flaws, is one of the essential demands in the design of composite materials, as manufacturing induced defects, or those generated during operation, can lead to catastrophic failure and dramatically reduce the mechanical performance. In this paper, we combine computational modeling and advanced multimaterial 3D printing to examine the mechanics of several different classes of defect-tolerant bioinspired hierarchical composites, built from two base materials with contrasting mechanical properties (stiff and soft). We find that in contrast to the brittle base constituents of the composites, the existence of a hierarchical architecture leads to superior defect-tolerant properties. We show that composites with more hierarchical levels dramatically improve the defect tolerance of the material. We also examine the effect of adding both self-similar and dissimilar hierarchical levels to the materials architecture, and show that the geometries with multiple hierarchical levels can retain a significant portion of their fracture strength in the presence of either large edge cracklike flaws or multiple small distributed defects in the material. We compare the stress distributions in materials with different numbers of hierarchies in both simulation and experiment and find a more uniform stress distribution in the uncracked region of materials with higher hierarchy levels. These results provide micromechanical insights into the origin of the higher defect tolerance observed in simulation and experiment.

Eshelby’s tensor and its connection to ellipsoidal cavity problems with application to 2D transformation problems in orthotropic materials

The relationship between Eshelby’s tensor and ellipsoidal cavity problems is established and discussed. With this connection, explicit expressions of Eshelby’s tensor are derived for orthotropic materials under plane strain condition and under anti-plane condition separately. Comparisons are made with an earlier form of Eshelby’s tensor, and components that were not previously published are explicitly given. As an application of the newly derived Eshelby’s tensor, elliptic inclusion problems with purely dilatational eigenstrains in orthotropic materials are solved. Stress distributions in materials of different symmetric classes are studied and discussed.

Study on Mould Structure of Differential Temperature Drawing Process for Magnesium Alloy

Magnesium alloy, differential temperature drawing, mould structure, surface roughness Abstract. To improve the formability of magnesium alloy sheet, the differential temperature drawing process was presented, and the mould structure of differential temperature drawing process for magnesium alloy was well-designed and fabricated by analyzing the friction and the stress distribution of material in drawing process. With the blank heated to 200-235°C at the flange by inserting heating coils and thermocouples in die and binder and the drawn cup cooled by injecting cooling water into die and punch, the differential temperature drawing process of magnesium alloy sheet was performed successfully and the value of surface roughness Ra1.6um was adopted for punch, Ra0.4um was adopted for die and binder. The result shows that by using the designed mould, the deep drawing performance of AZ31B magnesium alloy can be enhanced obviously and the value of LDR can be increased form 2.1 to 3.05.

A Review of Patented Methodologies in Instrumented Indentation Residual Stress Measurements

Quantification of residual stress distribution in materials is useful in the development, applications and quality control of engineering materials. Several residual stress measurement techniques are already well established for characterizing different engineering materials, while others remain largely unexplored. Yet for commercial success, the residual stress measurement methodologies must not only be efficacious but also cost-effective, introducing a potential dichotomy between the need for sophistication and ease of production. As reviewed in this article, there are encouraging results in developing patented methodologies in elasto-plastic (crack-free) instrumented indentation residual stress measurement of materials. Recent developments in instrumented indentation based residual stress measurement are likely to help reconcile the industrial and commercial pressure on improving materials performance and quality control. Keywords: Deformation, hardness, indentation, patents, residual stress, Young's modulus, instrumentation, commercial pressure, industrial pressure, force-displacement, thermal contraction

Computation and asymptotic analysis in the impact problem

Non-linear numerical method is applied to solve the viscous-elastic-plastic material impact problem. The finite element simulation agrees with the celebrated European crash safety analysis. The complex material stress distribution in the large deformation has been obtained, when the impact happens. Also the posteriorestimate solver and asymptotic analysis have been used for the sensitive pre-stage deformation before the impact happening. This part of simulation is very interesting for the passive safety in automotive protection devices. It is an important part of the mathematical modelling.

The Use of Moiré Patterns in TEM Images to Measure Precipitate Composition in Al-Si-Ge Alloys

Moiré patterns are commonly formed in multiphase system when diffracting planes of similar spacing and orientation lead to interference effects. They can be used experimentally to evaluate the stress distribution in materials [1], to analyze orientation relationships and latttice strain in diffraction contrast microscopy, or, combined with the related geometrical phase technique, to analyze displacements in high resolution lattice images [2,3]. The interpretation of moiré fringes is often not straightforward due to the elastic interaction between the crystals at the interface and the dynamical nature of electron diffraction [4]. However, if the two lattices are fully relaxed, or if a small precipitate crystal is embedded in a large matrix, moiré patterns can give a simple and direct measure of orientation and lattice constants. in the present work, the moiré technique has been applied to the quantitative analysis of lath-shaped Ge or Ge-Si precipitates in Al with the aim to determine the composition (the Si:Ge ratio) from the lattice parameter indicated by the moiré fringes.