Influence Of Material Anisotropy Research Articles

Influence of material anisotropy on the mechanics of surface damage

The problem of multiple cracks originating at free surface (surface damage) in an anisotropic material is considered. We focus on the effect of material anisotropy on the mechanics of crack interactions – in particular, on the suppressing effect of interactions on crack nucleation and growth under the tensile loading (stress shielding). Importantly, this effect may change to the opposite one of enhancement, under the shear loading. These effects strongly depend on the material anisotropy. Calculations were performed for the orthotropic materials and the effect of anisotropy was examined by case studies of specific configurations that included comparison with the case of the isotropic material.

A two-stage based model for partially-buried pile group response in cross-anisotropic saturated media adjacent to moving harmonic loads

The pile foundations are frequently affected by adjacent traffic loads except for general active loads. However, the dynamic responses of the pile groups under moving loads have been rarely reported before. In addition, the influence of material anisotropy is often neglected. In this paper, a three-dimensional (3D) analytical model for the dynamic analysis of partially buried pile groups in stratified saturated cross-anisotropic media under adjacent moving harmonic loadings is developed. Specifically, a 3D Bernoulli–Euler beam theory is adopted to simulate the monopile and then superimposed into the finite element (FE) formulation for the partially embedded pile groups. Subsequently, the basic solutions of layered saturated cross-anisotropic soils are derived by the analytical layer-element approach (ALEA). By combination with ALEA, the two-stage based boundary element (BE) equations for the pile-soil interface are obtained. Finally, by coupling the FE and BE formulations, the dynamical response equation of pile-soil is established. Based on the verification of the accuracy of the proposed methodology by comparisons with existing solutions and FE results from ABAQUS, the impacts of material anisotropy, pile buried length, loading velocity, and pile stiffness on the time-domain dynamic behavior of pile groups are analyzed. The results show that increasing the pile-buried ratio or pile stiffness reduces the magnitude of the dynamic response. Moreover, with the increase of material anisotropic parameters, the peak pile response decreases. And the peak dynamic response first increases and then reduces as the loading velocity increases.

Quantification of the influence of anisotropic plastic yielding on cold rolling force

Anisotropic mechanical properties in sheet material are of high importance, in particular for material to be used in stamping or deep drawing applications. The cold rolling process has a marked influence on the degree of anisotropy in the final product. However, the influence of material anisotropy on the cold rolling process itself has so far not been rigorously investigated. In this work, the degree of normal anisotropy is determined for two low-carbon steel grades after various degree of cold rolling reduction, both by X-ray diffraction as well as by tensile testing. The experimental work shows that material with high cold rolling reduction has non-negligible anisotropic properties; as a consequence the rolling force is seriously overestimated by cold rolling models with an isotropic yield criterion. It is therefore proposed to use the Hill48 yield criterion (instead of the von Mises criterion) in cold rolling models, this criterion takes anisotropic material behaviour into account. A comparison of cold rolling experiments with model predictions confirms that including the Hill48 yield criterion significantly improves the accuracy of a cold rolling model.

Influence of material anisotropy on void coalescence by necking for face-centered cubic single crystals

This paper presents the coalescence of microvoids embedded in an anisotropic copper single crystal using a micromechanics approach. Crystal plasticity framework was used to account for the anisotropy arising from the orientation and slip. A full 3D representative volume element (RVE) with void was considered to circumvent spurious loading. The constant load path parameters were enforced on the RVE using multi-point constraints. Various loading conditions that lead to necking were studied. The key finding from the present study is the interplay of the load path parameters (triaxiality and Lode parameter), material anisotropy, and initial void volume fraction on the void coalescence. It is noticed that at high triaxiality, the ductile failure mechanism is dominated by the necking mechanism, and at medium to low triaxiality, the ductile failure mode is a combination of shearing and necking mechanisms. It was observed that non-homogenous crystallographic slip manifests the material anisotropic effects in void cell RVE across various crystallographic orientations. The crystal orientation [110] exhibited higher shearing than the orientation [100] and [111]. Further, material anisotropy significantly affected void morphology but not the void coalescence strains at high triaxial values.

Reduction in Crosstalk between Integrated Anisotropic Optical Waveguides

The minimization of waveguide crosstalk is a long-standing challenge for optical engineers. Nowadays, the most popular technique to suppress crosstalk is anisotropic nanostructures, realized as subwavelength stripes between waveguides. However, the influence of material anisotropy on the efficiency of such structures remains unknown. In this work, we consider MoS2 waveguides separated by MoS2 stripes because this material has the record value of optical anisotropy. We discover that the use of MoS2 instead of Si results in a several-orders-of-magnitude-larger crosstalk distance. Therefore, we envision that by combining the extraordinary material properties with the known crosstalk-suppression methods, one can make the integration density of photonic devices close to electronics.

Influence of Material Anisotropy on the Interaction of a Crack with a Free Boundary

Influence of Material Anisotropy on the Interaction of a Crack with a Free Boundary

Effect of Initial Predeformation on the Plastic Properties of Rolled Sheets of AISI 304L Austenitic Steel.

This paper presents research on the influence of material anisotropy caused by the technological process of its manufacturing on the plastic properties of the material. In the experimental study, samples cut from an AISI 304L rolled sheet in the rolling direction, transverse, and at a 45° angle to the rolling direction were predeformed by axial deformation at 18 and 30%. The principal specimens extracted from the pre-deformed plates, cut in the longitudinal, transverse, and 45° angle directions, were subjected to tensile loading until failure. The data thus obtained allowed for the analysis of the plastic flow mechanism using the author’s calculation procedure. The CR coefficient analysis provided information on the state of plastic anisotropy caused by the pre-deformation. For the specimens predeformed in the rolling direction, plastic flow isotropy was observed at a strain of 35%. For the specimens predeformed in the transverse direction—the plastic anisotropy is completely removed at a strain of 33%. For the specimens predeformed at 45 degrees to the rolling direction, it was found that the strain completely removed the plastic anisotropy induced by rolling. The calculations provided information that due to an abrupt change in the strain path, a strong reconfiguration of the plastic flow mechanism occurs, causing the removal of anisotropy generated by rolling.

Additive manufacturing with fibre-reinforcement – design guidelines and investigation into the influence of infill patterns

PurposeFibre-reinforced additive manufacturing (FRAM) with short and continuous fibres yields light and stiff parts and thus increasing industry acceptance. High material anisotropy and specific manufacturing constraints shift the focus towards design for AM (DfAM), particularly on toolpath strategies. Assessing the design-property-processing relations of infill patterns is fundamental to establishing design guidelines for FRAM.Design/methodology/approachSubject to the DfAM factors performance, economy and manufacturability, the efficacy of two conventional infill patterns (grid and concentric) was compared with two custom strategies derived from the medial axis transformation (MAT) and guided by the principal stresses (MPS). The recorded stiffness and strength, the required CPU and print time, and the degree of path undulation and effective fibre utilisation (minimum printable fibre length) associated with each pattern, served as assessment indices for different case studies. Moreover, the influence of material anisotropy was examined, and a stiffness-alignment index was introduced to predict a pattern’s performance.FindingsThe highest stiffnesses and strengths were recorded for the MPS infill, emphasising the need for tailoring print paths rather than using fixed patterns. In contrast to the grid infill, the concentric infill offered short print times and reasonable utilisation of continuous fibres. The MAT-based infill yielded an excellent compromise between the three DfAM factors and experimentally resulted in the best performance.Originality/valueThis constitutes the first comprehensive investigation into infill patterns under DfAM consideration for FRAM, facilitating design and processing choices.

Scattering of plane waves by a 3D canyon in a transversely isotropic fluid-saturated layered half-space

Scattering of plane waves by a three-dimensional (3D) irregularity in a transversely isotropic (TI) fluid-saturated layered half-space is investigated for the first time. The derived exact stiffness matrix is applied to solve the dynamic response of free fields. The scattered fields, which arise from the presence of canyon irregularity, are described by applying dynamic Green's functions for uniformly distributed loads and pore pressure acting on an inclined plane, that is, the special indirect boundary element method (IBEM). The accuracy of the proposed method is verified via the comparison between the calculated results and those of published literature. By taking a semi-spherical canyon cut in a homogeneous, single-layered, and three-layered TI saturated half-space as examples, the influences of material anisotropy, boundary drainage condition, and sedimentary sequence on dynamic response are investigated. The results show that the material anisotropy and boundary drainage conditions all have a significant impact on the seismic responses, which is highly dependent on the waves type, incident angle, and frequency. For the layered medium, the displacement amplification is affected by the soil layer properties and sedimentary sequence.

Influence of the material anisotropy in the estimation of the yield strength with the Small Punch Test

The Small Punch Test (SPT) was developed in the 80’s as an alternative miniature test for the characterization of mechanical properties in the nuclear industry. One of the key aspects that materials must fulfill to be used with this miniature test is that of homogeneity and isotropy. The origin of the isotropy requirement comes from the fact that the estimation of mechanical properties using the SPT requires empirical correlations with standard tests, which generally show uniaxial stress fields. By contrast, the SPT shows a multiaxial stress field. There are few publications related with the influence of material anisotropy in the yield strength estimation using the SPT, and most of them are empirical studies. This research was intended to address, with a systematic finite element analysis, the influence that different anisotropy combinations could show in the yield strength estimation using the SPT. Thirty-six anisotropic hypothetical materials were evaluated with SPT simulations using the Hill’48 yield criterion. The yield strength of each material was estimated with the SPT using four correlation methods: Mao’s, CEN’s, the t/10 offset, and the optimized t/10. This study concluded that the SPT was not an appropriate test to evaluate or quantify the material anisotropy, but it was a valuable experimental test to estimate a mean yield strength of the six yielding stress components of the anisotropic material.

Forming Limit Prediction of Anisotropic Aluminum Magnesium Alloy Sheet AA5052-H32 Using Micromechanical Damage Model

This paper focuses on the implementation and applicable evaluation of a modified Gurson–Tvergaard–Needleman (GTN) damage model for predicting forming limit diagram of anisotropic aluminum alloy sheet, in which its elasto-plastic behavior is assumed to obey a non-quadratic anisotropic yield criterion. The original porous ductile material model is heuristically enhanced to suit anisotropy of sheet metal, and then, it is implemented via a user material subroutine using finite element codes of ABAQUS/Explicit software package. The material damage model is calibrated and applied to predict forming limit diagram of commercial aluminum alloy sheet AA5052-H32 via the Nakajima drawing tests under plane stress condition. To obtain various strain paths, the Nakajima tests are conducted for seven specimens, which are designed in accordance with standard ISO 12004-2-2008. The influence of material anisotropy on the predicted forming limit is also considered and discussed. The numerical simulation results obtained from the proposed damage model showed a good agreement with those of the experimental data.

Influence of material anisotropy on fatigue crack growth in C–Mn steels of existing structures

AbstractRolled steel plates and sections are often applied in structures in such a way that the principal load direction corresponds with the rolling direction. Examples are beams, arches, or pylons of bridges, supporting beams of ship decks, and the main elements of crane structures. However, some types of structure are subjected to a multiaxial stress state or are loaded with the main load direction perpendicular to rolling. The orientation may influence the mechanical properties. This paper studies the influence of anisotropy observed in the microstructure of rolled C–Mn steels on the tensile properties, Charpy impact values and particularly the fatigue crack growth rates. The influence of anisotropy is determined through tests performed at different orientations with respect to the rolling direction, namely, L‐T, T‐L and T‐S orientations. Samples were taken from structures that were constructed between 25 and 50 years ago from steel grades Fe510C or St52.3 (modern equivalences S355J2 or S355N). The orientation appears to have a statistically relevant influence on Charpy impact value and fatigue crack growth rate. The anisotropy ratio, defined as the ratio between the mechanical property in a certain orientation with that of the L‐T orientation, ranged between 0.30 and 0.53 for Charpy impact values. The anisotropy ratios appear correlated with the absolute Charpy value, with a correlation coefficient of ρ = −0.8. The anisotropy ratios of the crack growth in T‐L and T‐S orientations were 1.19 and 0.43, respectively. Anisotropy ratios for crack growth appear uncorrelated with anisotropy ratios for Charpy impact. The observed anisotropy may partially explain the difference between uniaxial and multiaxial fatigue crack growth as determined by others.

Anisotropy-Related Machining Characteristics in Ultra-Precision Diamond Cutting of Crystalline Copper

Deformation behavior at grain levels greatly affects the machining characteristics of crystalline materials. In the present work, we investigate the influence of material anisotropy on ultra-precision diamond cutting of single crystalline and polycrystalline copper by experiments and crystal plasticity finite element simulations. Specifically,diamond turning and in situ SEM orthogonal cutting experiments are carried out to provide direct experimental evidence of the material anisotropy-dependent cutting results in terms of machined surface morphology and chip profile. Corresponding numerical simulations with the analysis of built stress further validate experimental results and reveal the mechanisms governing the material anisotropy influence.The above findings provide insight into the fabrication of ultra-smooth surfaces of polycrystalline metals by ultra-precision diamond turning.

Phase field study the effects of interfacial energy anisotropy on the thermal migration of voids

While it is well known that inclusions (gaseous, fluid or solid) in a solid matrix would migrate under the driving force of a temperature gradient and the inclusion morphology is strongly affected by the material anisotropy, the influence of material anisotropy on the thermal migration of inclusions is still not clear. Via including an interfacial energy anisotropy into a phase field model of void migration driven by a temperature gradient, here we show that the interfacial energy anisotropy brings nontrivial effects on the void migration behavior. On the one hand, the void deformation during migration depends on the orientation of the anisotropy. On the other hand, a transverse velocity of the void appears if there is a misalignment between the symmetry axis of the anisotropy and the global temperature gradient direction. Such a transverse motion is due to the fact that the thermal diffusion flow becomes asymmetrically distributed around the void surface if the temperature gradient direction does not coincide with the symmetry axis of the anisotropy. The effects of the void size, the anisotropy parameter, and the thermal conductivity difference between the void and the matrix are discussed.

Residual ultimate strength of seamless metallic pipelines under a bending moment-a numerical investigation

Numerical investigation is conducted in this paper on both intact and dented seamless metallic pipelines (diameter-to-thickness ratio D/t around 21), deploying nonlinear finite element method (FEM). A full numerical model is developed, capable of predicting the residual ultimate strength of pipes in terms of bending capacity (Mcr) and critical curvature (κcr). The simulation results are validated through test results by using the measured material properties and specimen geometry. An extensive parametric investigation is conducted on the influences of material anisotropy, initial imperfection, friction of the test set-up and dent parameters. It is found that the structural response is quite sensitive to the frictions that have been introduced by the test configuration. For a pipe with a considerable dent size, the effect of manufacturing induced initial imperfection is insignificant and can be neglected in the FEM simulation. The material yield stress in the pipe longitudinal direction dominates the bending capacity of structures. In the end, formulas are proposed to predict the residual ultimate strength of dented metallic pipes under pure bending moment, which can be used for practical purposes. A satisfying fit is obtained through the comparison between the formulas and FEM methods.

Prediction of fracture initiation in square cup drawing of DP980 using an anisotropic ductile fracture criterion

This paper deals with the prediction of fracture initiation in square cup drawing of DP980 steel sheet with the thickness of 1.2 mm. In an attempt to consider the influence of material anisotropy on the fracture initiation, an uncoupled anisotropic ductile fracture criterion is developed based on the Lou—Huh ductile fracture criterion. Tensile tests are carried out at different loading directions of 0°, 45°, and 90° to the rolling direction of the sheet using various specimen geometries including pure shear, dog-bone, and flat grooved specimens so as to calibrate the parameters of the proposed fracture criterion. Equivalent plastic strain distribution on the specimen surface is computed using Digital Image Correlation (DIC) method until surface crack initiates. The proposed fracture criterion is implemented into the commercial finite element code ABAQUS/Explicit by developing the Vectorized User-defined MATerial (VUMAT) subroutine which features the non-associated flow rule. Simulation results of the square cup drawing test clearly show that the proposed fracture criterion is capable of predicting the fracture initiation with sufficient accuracy considering the material anisotropy.

Nonlinear quasi-static finite element simulations predict in vitro strength of human proximal femora assessed in a dynamic sideways fall setup

Osteoporotic proximal femur fractures are caused by low energy trauma, typically when falling on the hip from standing height. Finite element simulations, widely used to predict the fracture load of femora in fall, usually include neither mass-related inertial effects, nor the viscous part of bone׳s material behavior. The aim of this study was to elucidate if quasi-static non-linear homogenized finite element analyses can predict in vitro mechanical properties of proximal femora assessed in dynamic drop tower experiments. The case-specific numerical models of 13 femora predicted the strength (R2=0.84, SEE=540N, 16.2%), stiffness (R2=0.82, SEE=233N/mm, 18.0%) and fracture energy (R2=0.72, SEE=3.85J, 39.6%); and provided fair qualitative matches with the fracture patterns. The influence of material anisotropy was negligible for all predictions. These results suggest that quasi-static homogenized finite element analysis may be used to predict mechanical properties of proximal femora in the dynamic sideways fall situation.

The influence of material anisotropy and spiral welding on tensile strain capacity of spiral welded pipes

The longitudinal strain capacity of spiral welded pipelines displays to some extents unexplained behaviour. Therefore, they are not (yet) used extensively in offshore applications and harsh conditions, demanding a strain based design. An important factor that influences the tensile strain capacity is the quantity of anisotropy in terms of strength and toughness. Starting from an anisotropic hot rolled highstrength steel skelp, the process of helical forming and post-treating of the pipe adds heterogeneity and changes the level of anisotropy of the product. A parameter that should be examined with respect to anisotropy is the crack driving force, a measure for the toughness of the pipeline steel. Additional to the mode I loading (opening of the crack), the mode III component drives the in-plane shear motion of a crack in the spiral weld when the pipe is subjected to longitudinal deformation. This action, not present inlongitudinal welded pipes, shows a decreasing contribution with increasing plasticity. FE simulations have demonstrated a rise of crack driving force in anisotropic cases with respect to an isotropic reference. However, exact data and variation of various parameters, along with experimental testing need to be conducted. The outcome analysis of such simulations and tests can validate existing models, or help create a better understanding of anisotropic and heterogenic influences on the tensile strain capacity of spiral welded pipes.

Analysis of variance of tensile tests from spiral welded carbon steel tubes

Thick tubular carbon steel members are commonly used in combination with sheet piles in large retaining walls where they provide the necessary bending stiffness. A current international research project aims to provide safe and efficient design rules for such ‘Combitubes’. These tubes are usually manufactured by continuous spiral welding from a carbon steel coil. One of the key concerns is the possible influence of material anisotropy on the bending resistance of the resulting fabricated tube. Standard tensile tests were performed on several specimens extracted from such tubes, exploring the stress–strain behaviour in different orientations relative to the tube axes and the spiral directions. An analysis of variance (ANOVA) was then carried out to compare the mean values of properties deduced from these tests. This short paper offers statistical evidence that supports the view that an isotropic treatment may be acceptable for computational analyses and design of spiral welded steel tubes. It also illustrates how a standard statistical method may be applied to attempt such a validation, even though the data set may be too small for a rigorous statistical verification.

Materials Diagnostics: Non-Destructive Identification of Degraded Areas of Microstructure

The influence of material anisotropy on the exploitation performance of structural elements is recognized still insufficiently. The state seems to be the more evident if we consider that each type of materials inhomogeneity is not neutral in relation to its properties. In this field, carefully selected characteristics – the kind of microstructure diagnostics – delivers valuable data for the identification and quantification of desired material parameters deciding its usability. A separate problem is a spatial distribution of the parameters, which is an important feature of advanced, multi-functional materials with gradient-or/and layered structure. Further stages of the microstructure diagnostics covering the prediction of material behaviour in exploitation conditions and the estimation of the time of safe exploitation are still challenging research problems.The enumerated aspects of materials diagnostics require experimental data registered for the representative sample and suitable methods of data processing. Laboratory techniques and modelling procedures utilized in contemporary materials engineering deliver a wide range of computer-aided methodology, enabling one to obtain valuable characteristics of material, including crystallographic texture, residual stresses, phase composition, and crystallite size. In addition to methodological, experimental conditions play an important role in the outlined microstructure diagnostics. Both aspects are evident in the case of the identification of a subtle field of stresses resisted in the near-surface layer or in coating-substrate interface where a non-destructive way of examination is demanded. This work presents a selected non-destructive investigation of degraded areas of materials, recognized as critical from the viewpoint of the behaviour of a specific structural element in exploitation conditions.