Maximum Shear Stress Distribution Research Articles

Rolling Contact Fatigue Behaviors of 20CrNi2Mo Steel by a New Carbon and Nitrogen Composite Infiltration Process

ABSTRACTIn this paper, a new type of composite infiltration process was adopted for 20CrNi2Mo steel. Rolling contact fatigue (RCF) tests were carried out on the specimens treated with carburizing (C) and composite infiltration with carburizing and nitriding (C‐N). The results showed that after C and C‐N treatments were performed, the surface microhardness was increased by 78% and 114%, respectively, and the maximum CRS were −220 and −530 MPa. Moreover, the residual austenite volume fraction was controlled to approximately 10% for each treated sample. The fatigue limit of the C‐N sample was 11.3% higher than that of the C sample. The fatigue failure mechanisms are caused by the maximum shear stress distribution and surface roughness. The surface layer of the C‐N sample with higher hardness and more compressive residual stress inhibited the initiation of fatigue cracks, and the appropriate residual austenite in the carbon‐nitrogen infiltrated layer inhibited the propagation of fatigue cracks.

A New Method for Measuring Stress Inside Movable Element in Contact

Subsurface stress plays an important role in the damage of a movable contact element, but subsurface stresses are usually obtained with numerical calculation according to the theory of contact mechanics. In the present paper, a new method to measure the subsurface stress of the movable element is proposed with using photoelastic technology. Although the technology has been widely used in measuring the stress in the static state, it is seldom used in a moving body because the observed point is moving. After the experimental tester is introduced in detail, the principles of the photoelastic technology are presented. The tester is designed to be able to working in three conditions, the static, the rolling, and the sliding, in the line or surface contacts. The experimental results, that is, the interference fringes, of the three states are then presented in different loads and rotational speeds. Because the fringe figure indicates the maximum shear stress distribution in the body of the moving element, we can find what the real stress distribution in the rolling or sliding element is alike.

A higher-order morphoelastic beam model for tubes and filaments subjected to biological growth

Slender structures, in which width and thickness are much smaller than the length, are common in the natural world, such as wheat straws, bean sprouts, and biofilaments. Due to biological growth, these structures exhibit diverse morphological profiles with curling hairs, curling leaves, and twining plants as some examples. Accurate prediction of growth induced instabilities and corresponding shear deformation require a higher-order morphoelastic beam theory for growing tubes and filaments, for which we present a theory here. In the theory, the deformation gradient is decomposed into elastic deformation and growth using multiplicative decomposition. Appropriate assumptions for slender structures with circular cross-section are introduced and the displacement field and constitutive relations are derived from three-dimensional morphoelasticity. Corresponding variational principle is established and equilibrium equations are obtained. Our higher-order beam with growth theory can model growth-induced instability and shear deformation of growing tubes and filaments with circular cross-sections. Importantly, it can predict shear stress distribution and locations of maximum transverse shear stress in the circular cross-section. The shear stress, critical growth and post-buckling predictions of our proposed model and analytical solutions were validated by comparing its predictions against results from three-dimensional finite element simulations. Growth-induced instability and corresponding shear stress distributions were analyzed and the results are discussed. Our model can provide improved prediction for critical growth induced instabilities which are overestimated if the shear deformation is not considered.

Whole-Field Stress Sensing and Multiscale Mechanics for Developing Cement-Based Composites Containing Recycled Municipal Granular Wastes

Worldwide, there is a growing level of interest to develop sustainable cement-based products and processes in which the usage of natural resources such as sand and limestone are reduced from the current levels. One of the ways to achieve this is by replacing them with suitable inclusions of recycled granular materials from municipal wastes where possible. However, to understand the effects of such inclusions in concrete structures, research advancements are needed to sense and characterise the distribution of stresses (/strains) at the local scale and to establish their links with the fracture and bulk strength characteristics under external loading environments, which is the focus here. In this research, polyethylene (PE)-based granular materials derived from municipal wastes and fly ash obtained from the incineration of municipal solid wastes are used together as secondary raw materials in preparing the concrete mixtures. Photo stress analysis (PSA) is performed here, making non-contact and whole-field digital measurements of maximum shear stress distribution and the directions of the principal stresses at any point of interest on the surface of the samples under external loading. Their links with the fracture toughness and flexural strength of the samples cured at different times are presented. The novel PSA-based stresssensing helps to establish new understandings of the strength characteristics of composites across scales in the applications involving recycling and reusing conventional wastes and possibly in otherengineering applications in the future.

Effect of Behavior Patch and Aging Adhesive Exposed with Temperature in Modeling of a Damaged and Repaired Plate in Aluminum (2024-T3)

This work consists of the study is to analysis by the finite element method the effect of the ageing of the adhesive exposed simultaneously to the temperature and water on the degradation of its mechanical properties and consequently on the transfer of loads from the plate to patch. The stress intensity factor was evaluated according to immersion time and temperature. Several parameters have been taken into consideration, namely the properties of the composite patch, temperature, water absorption, rate and length of crack, the distribution of maximum shear stresses in the adhesive and peel in the patch were also analyzed.

Contact surface roughness analysis of pile and soil using ABS 3D printing materials

It is more difficult to measure the side resistance of the soil-structure contact surface during the pile pulling process. Only overcome the side resistance can be pulled out smoothly on the pile. Three kinds of test specimens were printed out by 3D printing equipment of the Acrylonitrile Butadiene Styrene (ABS) material to simulate the roughness of the soil-structure interface. The basic physical properties of two types of soil under the geological conditions of the pile to be pulled are tested through the geotechnical test, and the soil-structure constitutive theory and the roughness theory are introduced. The distribution of maximum shear stress at the contact surface is obtained by direct shear tests on the test specimens with different roughness, and the shear stage is analyzed with the contact surface. The results demonstrate that the mechanical properties of yellow clay are better than black clay for the two types of soil on the pile side. The shear stress changes with the increase of roughness and normal load during the direct shear process, which the maximum values of the two types of soil are at 60% of roughness and 300 kPa of normal load.

Modeling of photoelastic imaging of mechanical stresses in transparent solids mimicking kidney stones.

Theoretical and numerical models were developed to calculate the polariscopic integrated light intensity that forms a projection of the dynamic stress within an axisymmetric elastic object. Although the model is general, this paper addressed its application to measurements of stresses in model kidney stones from a burst wave lithotripter for stone fragmentation. The stress was calculated using linear elastic equations, and the light propagation was modeled in the instantaneous case by integrating over the volume of the stone. The numerical model was written in finite differences. The resulting images agreed well with measured images. The measured images corresponded to the maximum shear stress distribution, although other stresses were also plotted. Comparison of the modeled and observed polariscope images enabled refinement of the photoelastic constant by minimizing the error between the calculated and measured fields. These results enable quantification of the stress within the polariscope images, determination of material properties, and the modes and mechanisms of stress production within a kidney stone. Such a model may help in interpreting elastic waves in structures, such as stones, toward improving lithotripsy procedures.

Mechanical effects of residual bone mass, a maxillofacial prosthesis, and a reconstruction plate on the mandible after marginal resection.

In this study, analytic models were used to simulate marginal resection in the area of the second premolar to the second molar region, and the mechanical effects on the mandible of residual bone mass, a maxillofacial prosthesis, and a reconstruction plate were evaluated by three-dimensional finite element analysis. As residual bone mass decreased, maximum principal stress increased near the anterior ramus of the mandible, and maximum shear stress increased at the anterior buccal region of the resected area. In the mandible with a maxillofacial prosthesis, the maximum principal stress distribution at the anterior ramus was lower, and the distribution of maximum shear stress at the anterior buccal region of the resected area was higher. When a reconstruction plate was used, maximum principal stress and maximum shear stress were lower. Thus, lower residual bone mass was associated with increased mandible deflection and torsion. In addition, presence of a maxillofacial prosthesis decreased deflection but increased torsion, and presence of a reconstruction plate decreased deflection and greatly decreased torsion. These findings suggest that decreased residual bone mass and maxillofacial prostheses increase fracture risk; however, presence of a reconstruction plate was effective in decreasing torsional stress, thereby reducing fracture risk in the mandible.

Multidisciplinary Design Optimization of the Composite Cooling Structure for Nickel-based Alloy Turbine Blade

Abstract A designed method, multidisciplinary coupling computation and multiobjective optimization, has been established for the composite cooling structure of heavy gas turbine blade manufactured with a directionally solidified Ni-based superalloy. The method combines the one-dimensional fluid network gas-thermal coupling computation, three-dimensional flow field coupled with solid stress field, and anisotropic stress calculation based on finite deformation crystal slip. The temperature, flow field, Von-Mises stress and maximum resolved shear stress of the blade before and after optimization were analyzed. The results show that the optimized blade has lower maximum blade temperature, a more uniform temperature distribution, a lower flow resistance of the coolant channel at the leading edge than that of the original blade. The maximum Von-Mises stress of the optimized blade increases by 10.05 % more than the original blade. The maximum shear stress on the suction side and the pressure surface of the optimized blade are improved and slightly deteriorated compared with that of the original blade, respectively. The corresponding relationship of the maximum shear stress distribution with the local temperature gradient reveals further space for the improvement of the composite cooling structure. This paper has a particular guiding significance for the cooling structure design of the turbine blade.

Fill Factor Effects in Highly-Viscous Non-Isothermal Rubber Mixing Simulations

Abstract A finite volume technique in a commercial computational fluid dynamics (CFD) code is employed in this study to simulate transient, incompressible, non-Newtonian and non-isothermal rubber mixing. The simulation processes are conducted in a two-dimensional(2D) domain, where a mixing chamber partially-filled with rubber is equipped with a pair of two-wing non-intermeshing counter-rotating rotors. The main objective is to assess the effect of different fill factors of rubber on dispersive and distributive mixing characteristics by simulating 15 revolutions of the rotors rotating at 20 min−1. 50%, 60%, 70%, 75%, 80% and 90% are the six different fill factors chosen for the study. An Eulerian multiphase method has been applied to solve for the two different phases, rubber and air. The non-Newtonian property of rubber is handled using the shear rate dependent Carreau-Yasuda model, along with an Arrhenius function to include the temperature dependency. In addition to the governing equations related to the conservation of mass, momentum and energy, the volume of fluid (VOF) method is chosen to track the interface between air and rubber. With regard to the results, flow patterns, thermal distributions, viscosity behavior and volume fraction are analyzed for the different fill factors. In addition, dispersive and distributive mixing behavior is also assessed in detail using Lagrangian statistics, such as mixing index, cumulative distribution of maximum shear stress, cluster distribution index (CDI), scale of segregation (SOS) and length of stretch (LOS), calculated from massless particles. Both the Eulerian and Lagrangian results showed that fill factors between 70% and 80% presented the most reasonable and efficient mixing scenario, and also exhibited the best dispersive and distributive mixing characteristics combined.

Three-Dimensional, Non-Isothermal Simulations of the Effect of Speed Ratio in Partially-Filled Rubber Mixing

Abstract Three-dimensional, transient, non-isothermal calculations have been carried out using a commercial computational fluid dynamics (CFD) software in a two-wing rotor-equipped chamber partially-filled (75% fill factor) with rubber, to analyze the mixing efficiency for three different rotor speed ratios of 1, 1.125 and 1.5. The moving mesh technique has been used to incorporate the motion of the rotors. The Eulerian based volume of fluid (VOF) method has been used to track the interface between the two fluids, which are rubber and air. To assign the highly viscous and non-Newtonian properties of rubber, the Carreau-Yasuda model along with an exact Arrhenius formulation that accounts for the shear and temperature dependent viscosity, has been used here. Governing equations including the continuity, momentum and energy equations have been solved to characterize the flow field and various mixing parameters. Eulerian-based fields such as velocity magnitude, viscous heat generation, and average temperature and viscosity are compared between cases with different speed ratios. Dispersive and distributive mixing behaviour are assessed through a Lagrangian approach that tracks the paths of a set of massless particles. Statistical quantities such as cumulative distribution of maximum shear stress, cluster distribution index, and axial and inter-chamber particle transfer rates are calculated and presented as well. Results showed that the speed ratio of 1.5 displayed the best dispersive and distributive mixing characteristics in comparison to the other cases.

Rheological Property Criteria for Buildable 3D Printing Concrete.

Fresh concrete used in 3D printing should ensure adequate yield stress, otherwise the printed concrete layer may suffer intolerable deformation or collapse during the printing process. In response to this issue, an analytical study was carried out to derive the initial yield stress and hardening coefficient of fresh concrete suitable for 3D printing. The maximum shear stress distribution of fresh concrete was calculated using a stress transformation equation derived from the equilibrium condition of forces. In addition, the elapsed time experienced by fresh concrete during the printing processes was estimated and was then substituted into the elapsed time-yield stress function to calculate the yield stress distribution. Based on these results, an algorithm capable of deriving both the initial yield stress and the hardening coefficient required for printing fresh concrete up to the target height was proposed and computational fluid dynamics (CFD) analyses were performed to verify the accuracy of the proposed model.

NON-ISOTHERMAL EFFECTS IN PARTIALLY FILLED RUBBER MIXING SIMULATIONS OF MANUFACTURING PROCESSES

ABSTRACT A finite volume technique is used to analyze the isothermal and non-isothermal flow behavior for the rubber mixing process in a two-dimensional, partially filled (75%) internal mixer, which consists of two counterrotating rotors rotating at 20 rpm. In order to capture the interface between air and rubber, an Eulerian multiphase model called volume of fluid (VOF) has been employed here. The transient flow behavior was accomplished by a sliding mesh technique, and the highly viscous, non-Newtonian properties of the rubber have been characterized using the Bird–Carreau model. Most of the previous computational fluid dynamic (CFD)-based investigations of rubber mixing assumed isothermal flow, and consequently negligible viscous heat generation, temperature rise, and viscosity drop associated with heat generation. Hence, a non-isothermal simulation is carried out, and results are compared with those of an equivalent isothermal simulation. In addition, dispersive and distributive mixing characteristics are assessed using statistics calculated from particle tracks generated by a set of massless and neutral particles that have been injected in the simulation. For this purpose, quantities such as the cumulative distribution of maximum shear stress, length of stretch, and cluster distribution index are calculated and compared between isothermal and non-isothermal conditions. Results showed a significant difference between the isothermal and non-isothermal simulations, thus making the isothermal assumption critical. Also, the non-isothermal simulation predicted better mixing during the entire mixing cycle.

Thermal stress simulation of optimized SiC single crystal growth crucible structure

In order to reduce the dislocation density of SiC single crystal grown by PVT method, the thermal field was simulated based on finite element analysis. In this paper, VR-PVT SiC software was used to simulate the internal temperature gradient and thermal stress evolution caused by the different crucible structure. The change of crucible lid and sidewall structures has a better influence on radial temperature gradient and axial temperature gradient, respectively. Modified structure is a combination of these structures which improves both axial and radial temperature gradient. It reduces the maximum stress from 1.85 MPa to 1.58 MPa. The maximum shear stress and dislocation density distribution are shifted to the edge of the crystal. The optimization has only changed the external structure, so there is no conflict with the internal design.

Jagged cracking in the heat-affected zone of weld overlay on coke drum cladding

Abstract Jagged cracks were observed in SA240 Type 405 stainless steel cladding of Inconel 625 overlay repaired coke drums. It is found that intergranular cracking is the dominant fracture mode in the fine-grained heat-affected zone (FGHAZ) of the boat specimens. The sensitization effect from the operation and welding thermal cycles leads to the depletion of Cr with the preferential precipitation of Cr-rich M23C6 carbides along the grain boundaries. The cladding FGHAZ has the largest frequency of grain boundaries with higher local strain levels and the highest fraction of grain boundary Cr-rich M23C6 carbides. Thermal stress distributions predicted by finite element analysis clearly show the maximum shear stress to exhibit the typical “jagged” pattern near the cracked regions. Thermal expansion coefficient and strength mismatch among the shell base metal, cladding, and overlay is believed to have caused the unique jagged maximum shear stress distribution in the cladding HAZ of Inconel 625 overlay. The magnitude of this thermal stress can reach the yield strength of the cladding at 900 °F (482 °C) service temperature, therefore, provides the driving force for the jagged cracking formation in the sensitized HAZ.

Stability influence factors analysis and construction of a deep beam anchorage structure in roadway roof

Deep beam anchorage structures based on spatial distribution analysis of the cable prestressed field have been proposed for roadway roof support. Stability and other factors that influence deep beam structures are studied in this paper using mechanical calculations, numerical analysis and field measurements. A mechanical model of deep beam structure subjected to multiple loading is established, including analysis of roof support in the return airway of S1203 working face in the Yuwu coal mine, China. The expression of maximum shear stress in the deep beam structure is deduced according to the stress superposition criterion. It is found that the primary factors affecting deep beam structure stability are deep beam thickness, cable pre-tension and cable spacing. The variation of maximum shear stress distribution and prestressed field diffusion effects according to various factors are analyzed using Matlab® and FLAC3D™ software, and practical support parameters of the S1203 return airway roof are determined. According to the observations of rock pressure, there is no evidence of roof separation, and the maximum values of roof subsidence and convergence of wall rock are 72 and 48 mm, respectively. The results show that the proposed roof support design with a deep beam structure is feasible and achieves effective control of the roadway roof.

Photonics and fracture toughness of heterogeneous composite materials

Fracture toughness measures the resistance of a material to fracture. This fundamental property is used in diverse engineering designs including mechanical, civil, materials, electronics and chemical engineering applications. In spite of the advancements made in the past 40 years, the evaluation of this remains challenging for extremely heterogeneous materials such as composite concretes. By taking advantage of the optical properties of a thin birefringent coating on the surface of opaque, notched composite concrete beams, here we sense the evolution of the maximum shear stress distribution on the beams under loading. The location of the maximum deviator stress is tracked ahead of the crack tip on the experimental concrete samples under the ultimate load, and hence the effective crack length is characterised. Using this, the fracture toughness of a number of heterogeneous composite beams is evaluated and the results compare favourably well with other conventional methods using combined experimental and numerical/analytical approaches. Finally a new model, correlating the optically measured shear stress concentration factor and flexural strength with the fracture toughness of concretes is proposed. The current photonics-based study could be vital in evaluating the fracture toughness of even opaque and complex heterogeneous materials more effectively in future.

Numerical simulations of partially‐filled rubber mixing in a 2‐wing rotor‐equipped chamber

ABSTRACTPartially filled internal batch mixers are used for mixing of rubber compounds in the polymer industry. The use of mixing in such mixers equipped with a rotor is critical to the process itself, and hence, understanding of mixing is important in terms of evaluating how various operating parameters such as rpm, fill factor, and ram pressure affect distribution and dispersion of materials. The objective of the current study is to gain valuable insights on the influence of fill factor, which is the volume of the material relative to the volume of the chamber. Two‐dimensional (2D) computational fluid dynamics (CFD) simulations of rubber mixing in a 2‐wing rotor‐equipped chamber are presented here, for the first time, for fully‐filled/100% and partially‐filled/75% chambers. The volume‐of‐fluid (VOF) technique is employed to capture the interface between the rubber and air in partially filled isothermal simulations. Flow patterns are visualized to analyze the material movement. Massless particles are injected and various statistics are calculated from their positions in order to compare dispersive and distributive mixing characteristics between the fully‐filled and partially‐filled cases. Specifically, quantities such as mixing index and the maximum shear stress distribution history of particles are analyzed to obtain information about dispersive mixing, while length of stretch and cluster distribution index, also calculated from particles, are presented to investigate distributive mixing capabilities. All the results consistently demonstrated the superior effectiveness of partially‐filled mixing chambers in terms of their dispersive and distributive mixing characteristics in comparison to fully‐filled chambers. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44250.

Shear stress distribution within narrowly constrained structured grains and granulated powder beds

An experimental study is presented here to understand the stress transmission characteristics under different geometrical arrangements of particulates inside a narrow chamber subjected to axial compression loading. The multi-grain systems considered here are face-centred, simple cubic and poly-dispersed structures, as well as inclusions embedded inside seeded, unseeded and cohesive powder bed of Durcal (calcium carbonate). The distribution of the maximum shear stress, direction of the major principal stress and shear stress concentration factor were obtained using photo stress analysis tomography (PSAT). The results show that the maximum shear stress distribution in the simple cubic structure is chain-like and self-repetitive, i.e., a single grain behaviour is representative of the whole system. This is not the case in the case of other granular packing. In the case of the inclusion surrounded by powder media, the maximum shear stress distribution in the inclusion occurs through ring-like structures, which are different from those observed in the structured granular packing. This tendency increases for an increase in the cohesivity of the surrounding particulates. In the granular systems, the direction of the major principal stress is mostly orthogonal to the direction of loading except in some particles in the random granular packing. In the case of inclusion surrounded by Durcal particulates, the directional of the major principal stress acts along the direction of the axial loading except in the ring region where this tends to be oblique to the direction of axial loading. Estimates of the shear stress concentration factor (k) show that, k tends to be independent of the structural arrangement of granular packing at higher load levels. In the case of inclusion surrounded by powder bed, k for the seeded granulated particulate bed is mostly independent of the external load levels. In the case of unseeded particulate (granulated) bed, a fluctuation in k is observed with the loading level. This suggests that the seeded granules could distribute stresses in a stable manner without much change in the nature of shear stress-transmitting fabric of the particulate contacts under external loading. An increase in the cohesion of particulate bed results in more plastic deformation as shown by the differential shear stress concentration factor. The results reported in this study show the usefulness of optical stress analysis to shed some scientific lights on unravelling some of the complexities of particulate systems under different structural arrangements of grains and surrounding conditions of the inclusions in particulate media.

Micromechanical analysis of inclusions in particulate media using digital photo stress analysis tomography

An experimental study aimed at sensing the stress distribution characteristics of inclusions inside particulate assemblies subjected to axial compaction is presented. The particulate assemblies are made of powders and grains, in which photoelastic inclusions are embedded along the central axis of the assemblies at different elevations. Digital photo stress analysis tomography is used to obtain the contours of maximum shear-stress distribution and the direction of major principal stress within the inclusions under the external loading. Using this, an analysis is performed for understanding the implications of using Hertz theory based on discrete element modeling for simulating stresses in relatively big inclusions surrounded by particulates. In the case of the inclusions surrounded by the grains, the location at which the peak value in maximum shear stresses occurs within the inclusions deviates from that of Hertzian analysis. This effect is dominant in the case of inclusions residing close to the loading surface. Unlike granular materials, shear-stress distribution characteristics of inclusions in powder surroundings tend to display continuum-like behavior under external compression and points to the need for a deeper understanding of the effects of the surrounding materials in particulate beds with inclusions.