Maximum Stress Concentration Research Articles

Fracture Characteristics and Analysis in Dissimilar Cu-Al Alloy Joints Formed via Electromagnetic Pulse Welding.

The aim of this study was to identify and analyze the fatigue fracture characteristics of dissimilar Al 6061 to Cu (UNS C11000) lap joints made with ultrafast electromagnetic pulse welding (EMPW) via fractography, stress analysis and finite element simulation. It was observed that EMPW generated an annular (or ring-shaped) bonding area, with weld zones and a central non-weld zone when viewed from the cross section. Two types of failure modes occurred in relation to the cyclic loading levels: base metal fracture or transverse through-thickness (TTT) crack growth at a higher loading level, and joint interfacial failure at a lower loading level. In the interfacial failure, fatigue crack initiated from the outer edge of annular welding area, and propagated to form an approximate elliptical boundary. Fatigue crack propagation was characterized by fatigue striations existing in discrete areas on the fracture surface. This was attributed to a coupled role of shear and normal stresses present in a tensile lap shear sample due to the bending moment caused by the inherent misalignment. The final rapid fracture started from elliptical boundary with elongated shear dimples. Both theoretical stress analysis and finite element model revealed the maximum stress and stress concentration along the outer edge, where fatigue crack initiation occurred.

Evaluating Damage Accumulated in Car Wheelset Axle Journals by the Ultrasonic Method Using Rayleigh and Head Waves

We propose a method and facility for measuring the speed of Rayleigh and head waves in order to study the loss of structure in the metal of the surface layer of car wheelset axle journals resulting from long-term operation. It has been discovered that the transit times of surface and head waves near the end and the fillet transition to the pre–wheel-seat part of the axle journal differ, a fact that indicates the presence of microdefects in the surface area of the fillet transition of axle journals accumulated after long-term operation. A criterion is proposed for assessing damage accumulated in the zone of maximum stress concentration in the surface layer of the fillet of car wheelset axle journals.

Stress concentration around of pin-loaded hole in unidirectional multi-layered metallic matrix composite material

The objective of this study is to examine the stress concentration factor around a pin-loaded hole in a metallic matrix composite material, analytically and numerically. It is assumed that all unidirectional fibers lie in the metallic matrix while the shear stress in fibers is discarded. To generally derive the equilibrium equation for all fibers and the metallic matrix, the previous shear-lag theory had been improved and the extension in the metallic matrix was considered. Afterwards, the equilibrium equation was solved by the eigenvalue method while the displacement field and stress distribution around the pin-loaded hole were computed. Having calculated stress concentration factors and the displacement field in a unidirectional multi-layered composite material, we compared the analytical results with those numerical values from other references. Additionally, the effect of the pin’s diameter, as well as the edge-hole distance on maximum stress concentration factor was investigated. To recapitulate, it is seen that the modified shear-lag theory can simulate the mechanism of the load transfer between metallic matrices.

Finite-element analysis and optimization of the mechanical properties of polyetheretherketone (PEEK) clasps for removable partial dentures

PurposePolyetheretherketone (PEEK), a high-strength, aesthetic, and non-allergic thermoplastic polymer, recently became a candidate for replacing metallic components in dental prosthesis. However, as PEEK is flexible, the need for retention presents a key challenge in terms of its clinical application. In this study, clasps prepared using PEEK were optimized and evaluated to provide the mechanical properties required by dentures. MethodsSeventy-two three-dimensional rod-shape models, based on four thickness/width ratios, three base widths, and six taper ratios were created. These models were analyzed using finite-element methods to determine which modified clasp arm shape provided the most appropriate mechanical properties. Three shape-optimized PEEK specimens and one standard-shape Co–Cr alloy specimen were then fabricated. Constant-displacement fatigue testing was performed to calculate load values and deformations after ten years of clinical use. ResultsShape optimization indicated a maximum stress concentration that was consistently located at the base of the specimen, a correlation between mean load values and thickness that was greater than that with the width, and a correlation between taper ratio and mean load values. Fatigue testing showed that although PEEK exhibited significantly lower average load values than the Co–Cr alloy, these were sufficient for clinical use. All specimens exhibited significant deformation during the first period of cycling; however, there was no significant difference in the deformation between the two materials after fatigue testing. ConclusionsPEEK exerts fewer stresses on abutments compared to standard-alloy clasps, provides adequate retention, and satisfy aesthetic demands, indicating that PEEK presents a promising alternative to conventional metal clasps.

Waste rock filling in fully mechanized coal mining for goaf-side entry retaining in thin coal seam

A large amount of waste rock is generated during thin seam coal mining operations underground. The waste rock material stacked on surface also adds to the environmental pollution. So it is important to reduce the amount of waste rock by exploring gainful utilization methods. This paper deals with an investigation undertaken to develop an alternate gob filling material in laboratory and evaluating its efficiency numerically as well as in field. A coal–waste rock separation system and a roadway layout system were designed, and a new technique of fully-mechanized goaf-side entry retaining and goaf filling back hydraulic supports was proposed. These methods helped realize the goal of green mining, which was featured by waste rock consumption in nearby region without any need to be elevated to ground surface. This study demonstrated that the two proposed mining methods, namely, caving mining method and mining with filling method, differed in mechanical environments where roadside filling body was located, deformation, and failure scope. The maximum principal stress concentration degree near the roadside filling body for caving mining method was high with a maximum value of 42.5 MPa because of key rock blocks in overburden. As a result, the surrounding rock of roadside filling body was severely deformed with a maximum displacement of 1117 mm. The entire roadside filling body moved toward the inside roadway and experienced plastic failure. After goaf filling, filling bodies in goaf, roof and floor strata, and roadside were combined to form an entire withstanding deformation. The motion space of overburden rock was limited, the adjustment range of surrounding rock stress near the roadside filling body was narrowed, the maximum principal stress decreased to 29.5 MPa, and the main roof did not rupture. Accordingly, the deformation of surrounding rocks of the roadside filling body was small, the maximum displacement of roof and floor was 457 mm, and the roadside filling body did not experience plastic failure. The study results enrich goaf-side entry retaining theory in thin coal seam and mechanized filling technology and provide a theoretical foundation for thin coal seam mining with difficulty in waste rock treatment.

Convergent evolution inspired serrated structure for improving efficiency of soil imprinting and its mechanism investigation

Remarkable geometrical similarities are found in digging claws of soil burrowing animals, in spite of the fact that they evolved independently. Based on convergent evolution theory, this study innovatively proposed a bionic engineering perspective that focuses on general and analogous geometrical characteristics of soil animals. It was observed that soil animals with powerful burrowing ability have analogous serrated structures on their digging claws. Taking soil imprinting toothed wheel as the research object, the hypothesis that special serrated structures have the potential of reducing penetrating resistance from soil and enhancing digging efficiency for soil engaging component was investigated. The convergent evolution inspired bionic serrated structures were utilized for the design of cutting edge on toothed wheel. Then, a toothed wheel that mounted with the conventional tooth and a bionic tooth were manufactured and tested in the soil bin. Results showed that special bionic serrated structure could reduce the required draft force for toothed wheel; meanwhile increase the depth and volume of prepared micro-basin. It was found that the soil-penetrating mechanism of the bionic toothed wheel behaved as saw cutting that similar to the digging behavior of soil burrowing animals. Geometry of serrated structure has the ability to maximum stress concentrations in soil, thus increased the tendency of soil material to fail. These results indicate that the convergent evolution inspired bionic approach is novel and advantageous for the design of new soil engaging implements for working quality optimization and forward resistance reduction. Keywords: convergent evolution, bionic serrated structure, soil imprinting, soil-engaging component, bionic agricultural machinery DOI: 10.25165/j.ijabe.20191204.3638 Citation: Zhang Z H, Li Y, Tong J, Carr S. Convergent evolution inspired serrated structure for improving efficiency of soil imprinting and its mechanism investigation. Int J Agric & Biol Eng, 2019; 12(4): 16–26.

Investigation into the effect of lateral and longitudinal loads on railroad spike stress magnitude and location using finite element analysis

Multiple wide-gage derailments have recently been attributed to broken spikes in track constructed with premium elastic fastening systems. Premium fasteners on timber crossties were introduced into heavy axle load (HAL) freight service in North America over the past few decades and have gained popularity given they are thought to reduce maintenance costs, reduce rail-rollover risk, and they do not generally require rail anchors. However, given recent derailments and identification of failed spikes during field testing at higher rates than traditional fasteners, the University of Illinois at Urbana-Champaign is investigating the stress state of cut spikes in premium fasteners. This paper provides background on the broken spike problem and initial results from a validated finite element model that was developed to quantify the magnitude and location of spike stress concentrations as load magnitude, load direction, and crosstie species are varied. Results from this study indicate that the longitudinal loading, which is not generally present in traditional cut spike fasteners, is more detrimental to the performance of the spike than lateral loading. Further, the depth to the maximum stress concentration increases as the ratio of longitudinal to lateral load increases. Finally, as crosstie species is varied, the magnitude and depth of spike stress changes; these changes are more likely driven by changes in compressive and shear strengths, and then by modulus. Results from this work are presented in an effort to provide information which can be used to mitigate field failures by reducing the spike stresses in an effort to increase the overall safety of HAL freight rail networks and increase the life cycle of premium spike fastening systems.

Finite Element Analysis of Fatigue Crack of Square Bird-Beak X-joints Under Brace Axial Loading

This paper presents a numerical study of the fatigue crack propagation of square bird-beak hollow section welded X-joints. A pair of axial forces were applied at the brace ends, while the chord ends were free. Finite element modelling was done in ABAQUS while FRANC3D was used for the computation of stress intensity factor and crack propagation. The initial crack inserted at the site of maximum stress concentration. Paris’ law was used to compute the fatigue life. The results obtained from the finite element analysis compared with the experimental data, and the predicted crack growth was found to be in good agreement with the test observations. For such joints, the surface cracks length vs. fatigue crack growth curve proposed to ensure practicability in real applications.

Connection between strength and thermal conductivity of metal matrix composites with uniform distribution of graphite flakes

The paper focuses on the connection between thermal conductivity and overall strength of metal matrix composites on example of Al2024 and Mg-0.9Ca alloys reinforced with graphite flakes. We combine theoretical and experimental approaches to analyze the maximal stress concentration in such composites as a function of minimal distance between graphite flakes. The latter is linked to the volume fraction of the inhomogeneities, which governs overall thermal conductivity. Elimination of the volume fraction parameter leads to the explicit cross-property connection. This approach is possible if inhomogeneities in the material have the same shape and are uniformly distributed with no distinguishable clusters. The agreement between the theoretical predictions and experimental observations is very good.

Effect of Implant-Abutment Connection Type on Stress Distribution in Peri-Implant Bone and Abutment Micromovement: A Three-Dimensional Finite Element Analysis.

This study assessed the effect of implant-abutment connection type on stress distribution in peri-implant bone and abutment micromovement using finite-element analysis (FEA). Dimensions of three implant-abutment designs were measured by a three-dimensional scanner and transferred to SOLIDWORKS. An elemental model was designed using ABAQUS. Each implant was placed in bone at the crestal level. A 100-N load was applied at a 45° angle relative to the longitudinal axis of the implant in the buccolingual direction from the palatal toward the buccal and coronal parts of the abutment. Shear stress, von Mises stress, and micromovement of the abutment relative to the fixture were analyzed. Data were reported qualitatively and quantitatively using ABAQUS. The von Mises stress in all three samples decreased from the crest toward the apical area and was distributed homogenously. Maximum stress concentration was at the most coronal part of the implant body in the midbuccal area. In cancellous and cortical bone, stress decreased from the crest toward the palate and was at its maximum at the midbuccal point in the bone crest. Stress in cortical bone was more homogenous and in cancellous bone was higher. Shear stress was higher in the buccal than in the palatal area, and at its maximum shear stress and equal in the mesiobuccal and distobuccal areas. Micromovement was 4.25 μm in an Astra implant, 5.42 μm in a Intra-Lock implant, and 6.63 μm in an SPI implant. The distribution of von Mises and shear stress was the same in bone around the three implant connection types; however, abutment micomovement differed.

Comparison of Stress Patterns in Edentulous Mandibular Bone Around Two Implant Retained, Four Implant Retained Overdenture and All-On-Four Concept-A 3 Dimensional Finite Element Analysis

Recently the use of tilted implants has been considered as a preferable option in case of atrophic edentulous arches. The tilted longer implants can be of use to ward off the important anatomical structures while also permitting cantilever reduction. Since the load transfer mechanism of an implant can be altered significantly by the number of implants and its location in the edentulous ridge, the present study evaluates and compares the stress patterns in the edentulous mandibular bone around two implant retained, four implant retained over denture and all on four concepts under different loading conditions using finite element analysis. Purpose: The biomechanical behaviour of the ‘All-On-Four’ system was compared with that of the two implant-supported and four-implant supported mandibular overdenture using the three dimensional finite element method (FEM). Thereby evaluating the von Misses stresses induced on the implants under different loading simulations. Materials & Method: Three dimensional models representing mandible restored with ‘All-On-Four’, two implant-supported and four-implant-supported prosthesis were developed in the three dimensional design software and then transferred into FEM software. The models were then subjected to four different loading simulations (full mouth biting, canine disclusion, load on cantilever, load in the absence of cantilever). The maximum von Mises stresses were localized and quantified for comparison.1 Results: Among the three models, under all loading simulations, the maximum stress concentrations werealong the neck of the implant. The stress levels for full mouth loading simulation was highest for twoimplant supported overdenture design and the least for All-On-Four overdenture design. In all three designs,the least stress was when the implants were loaded in a lateral direction. The stress levels for cantilever andnon-cantilevered designs were nearly the samefor all the simulated designs. Conclusion: When tested under differentloading simulations, the three modelsshowed similar location and distribution ofstress patterns. Thus from the study it can beconcluded that the All-On-Four Concept is a clinically applicable treatment option for the atrophic edentulous ridges and induces least amount of stresseson the edentulous ridges. Therefore the overall longevity of the prosthesis is greatly enhanced.

Convergent evolution inspired serrated structure for improving efficiency of soil imprinting and its mechanism investigation

Remarkable geometrical similarities are found in digging claws of soil burrowing animals, in spite of the fact that they evolved independently. Based on convergent evolution theory, this study innovatively proposed a bionic engineering perspective that focuses on general and analogous geometrical characteristics of soil animals. It was observed that soil animals with powerful burrowing ability have analogous serrated structures on their digging claws. Taking soil imprinting toothed wheel as the research object, the hypothesis that special serrated structures have the potential of reducing penetrating resistance from soil and enhancing digging efficiency for soil engaging component was investigated. The convergent evolution inspired bionic serrated structures were utilized for the design of cutting edge on toothed wheel. Then, a toothed wheel that mounted with the conventional tooth and a bionic tooth were manufactured and tested in the soil bin. Results showed that special bionic serrated structure could reduce the required draft force for toothed wheel; meanwhile increase the depth and volume of prepared micro-basin. It was found that the soil-penetrating mechanism of the bionic toothed wheel behaved as saw cutting that similar to the digging behavior of soil burrowing animals. Geometry of serrated structure has the ability to maximum stress concentrations in soil, thus increased the tendency of soil material to fail. These results indicate that the convergent evolution inspired bionic approach is novel and advantageous for the design of new soil engaging implements for working quality optimization and forward resistance reduction. Keywords: convergent evolution, bionic serrated structure, soil imprinting, soil-engaging component, bionic agricultural machinery DOI: 10.25165/j.ijabe.20191204.3638 Citation: Zhang Z H, Li Y, Tong J, Carr S. Convergent evolution inspired serrated structure for improving efficiency of soil imprinting and its mechanism investigation. Int J Agric & Biol Eng, 2019; 12(4): 16–26.

A Stress concentration factor for interacting surface notch and subsurface hole

We propose a conservative method for the calculation of the maximum stress concentration factor (SCF) for an interacting notch-hole pair and for a double semi-circular notch (i.e., a notch that has an additional small semi-circular notch ahead of its tip). The method is based on a linearly elastic Airy stress function solution for a circular hole. The notch-hole and double notch configurations are aligned vertically with respect to uniform uniaxial (horizontal) stress. This means, a uniform horizontal tension is applied to a notch-hole pair that lie on a vertical axis. For the notch-hole pair, the maximum interacting SCFs are calculated for edge to edge gaps equal to hole sizes of 2.5a, 5a, 10a and 15a, where a is the hole radius. The analytical results are validated by 2-D finite element calculations. The presented simple approach provides good results with errors well below 10% in most cases compared to the detailed finite element analyses. Fatigue notch factors that can be thought of as the effective SCFs in fatigue analyses are determined. By using the simple approach, computationally costly finite element analysis can be avoided.

Discrete‐Continuum Duality of Architected Materials: Failure, Flaws, and Fracture

Abstract3D nano‐ and micro‐architected materials are resilient under compression; their susceptibility to flaws and fracture remain unexplored. This work reports the fabrication and tensile‐to‐failure response of hollow alumina nanolattices arranged into 5 µm octet‐truss unit cells. Some specimens contained through‐thickness center notches oriented at different angles to the loading direction, with a length‐over‐sample‐width ratio of 0.45. In situ tensile experiments reveal that for all orientations, failure initiates at the notch root, followed by instantaneous crack propagation along lattice planes orthogonal to extension. A tensile strength of 27.4 ± 0.7 MPa is highest for unnotched samples and decreases as notch orientation varies from 0° to 90° to its minimum, 7.2 ± 0.4 MPa; their specific tensile strength is ≈4 × higher than that for all other low‐density materials. Finite element simulations reproduce observed strengths and failure mechanisms: initial cracks always initiate at the nodal junctions with highest stress concentrations by tearing of alumina walls at the nodes. Subsequent crack propagation shifts maximum stress concentration to the nodes along lattice plane orthogonal to the loading direction. A modified analytical fracture model based on the effective notch length predicts tensile strengths consistent with experiments. These findings imply that continuum fracture mechanics can predict failure in nano‐architected materials, which helps develop advanced materials through informed architectural design.

Optimum design of perforated symmetric laminates using evolutionary algorithm

Here, analytical studies have been carried out to determine the optimal values of effective parameters on the stress concentration factor around a cutout using genetic algorithm. Optimum designs of single lamina as well as symmetric laminates with 4, 8 and 12 layers of graphite/epoxy and glass/epoxy plates containing a circular cutout with various sizes are presented. The work focuses on extending the analytical solution given by Greszczuk to determine the stress distribution in multilayered composite plates subjected to arbitrary in-plane loadings. This is achieved by introducing an arbitrary oriented uniaxial, biaxial and shear loading conditions into Greszczuk solution. In order to mimic as much as possible the real structural behavior, the finite-width correction factor given by Tan is used. Effective parameters on stress distribution around the circular cutout in composite plates considered as design variables include: load angle, fiber orientation, cutout size and stacking sequence of the laminate. The objective function in this study is the minimization of maximum stress concentration around the cutout which is calculated by the present analytical solution. The first ply failure load predicted using Tsai–Wu criterion is maximized for both single lamina and symmetric laminates. Also, the weight of the plates is minimized by increasing the hole size to width ratio. The results obtained by the present analytical solution compare favorably with those obtained using complex variable method. For laminated plate subjected to shear loading, the stress concentration factor decreased drastically by 48.79% compared to a single lamina. The failure load is also increased in most of the loading cases. The results also showed that the genetic algorithm code converges rapidly in most of the cases. The accuracy, quickness, low computational cost and the simplicity of the present solution encourage the designers to use it in practical applications.

Analysis of inclusion in thermoelectric materials: The thermal stress field and the effect of inclusion on thermoelectric properties

This paper analyses a two-dimensional problem in thermoelectric materials with an inclined elliptic inclusion. We have obtained the closed-form solutions of electric current density and temperature considering the inclusion's electrical and thermal permeability. Based on the derived thermoelectric field, the thermal stresses are given in the explicit form and the effect of inclusion on effective thermoelectric properties is investigated. The electrically impermeable and thermally impermeable inclusions will respectively cause maximum electric current concentration and heat concentration. The thermally impermeable and rigid inclusion will cause maximum stress concentration around the inclusion. Furthermore, we find that the effective electric conductivity (effective thermal conductivity) of the matrix-inclusion system is increased when the inclusion have higher electric conductivity (thermal conductivity) than the matrix. It is possible to enhance the effective figure of merit by inserting inclusions with specific electric conductivity and heat conductivity. It predicts a new way for the design of high-performance thermoelectric devices. The results in this paper can be directly used for reliability consideration in design and optimization of thermoelectric devices in engineering.

Parametric study and equations of the maximum SCF for concrete filled steel tubular T-joints under in-plane and out-of-plane bending

Due to being increasingly used in infrastructure, studying stress concentration in concrete-filled steel tubular joints is necessary. In this study, the variation of the maximum Stress Concentration Factor (SCFmax) with non-dimensional geometric parameters in steel circular hollow section brace welded to concrete-filled circular hollow section chord (CHS-to-CFCHS) T-joints under in-plane and out-of-plane bending moment has been investigated. A database of the maximum SCFs in CHS-to-CFCHS T-joints under in-plane and out-of-plane bending moment is developed based on three-dimensional (3D) finite element (FE) models. The 3D FE models developed using ABAQUS software, have been verified using experimental results. Graphs showing variation of the maximum SCF, in CHS-to-CFCHS T-joints, with non-dimensional geometric parameters have been produced and compared with those for non-filled empty T-joints. Parametric equations for predicting the maximum SCFs in CHS-to-CFCHS T-joints under in-plane and out-of-plane bending moment have been developed in a multiple nonlinear regression analysis. There is a good agreement between the maximum SCFs predicted by the parametric equations and those determined from the experiments.

Modelling of the tooth contact through one-layered mouthguard

The work deals with the modelling of the contact of the teeth with and without taking into account a single-layer mouthguard made of ethylene vinyl acetate (EVA). The problem is considered in an axisymmetric formulation with the contact interaction including a friction along the conjugate surfaces. An optimal finite element mesh with a gradient dense element distribution near to the contact areas was used. A series of numerical experiments for various values of indentation force (ranging from 50 to 500 N) was carried out, a significant drop in the intensity of stress in hard tissues of the teeth was established by more than 60% when using a mouthguard. In this case, the zone of maximum stress concentration is not of a local nature, as in contact without taking into account the mouthguard. The dependences of the maximum level of stress intensity for two variants of design schemes and the intensity of plastic deformations on the strength of indentation are obtained. The distributions of contact pressure and tangential stress are obtained, it is found that the maximum contact pressure for the model taking into account the mouthguard is 3 times less than in the model without taking into account the prototype structure.

Numerical simulation and analysis of thermal stress distributions for a planar solid oxide fuel cell stack with external manifold structure

A three-dimensional numerical model based on the finite element method (FEM) is constructed to calculate the thermal stress distribution in a planar solid oxide fuel cell (SOFC) stack with external manifold structure. The stack is composed of 5 units which include cell, metallic interconnect, seal and anode/cathode current collectors. The temperature profile is described according to measured temperature points in the stack. It can be clearly seen that the maximum stress concentration area appears at the corner of the components when the stack is heated from room temperature (RT) to 780 °C. The effects of stack components on maximum stress concentration have been investigated under the operation temperature, as well as the thermal stress simulation results. It is obvious that the coefficient of thermal expansion (CTE) mismatch between the interconnect and the seal plays an important role in determining the thermal stress distribution in the stack. However, different compressive loads have almost no effect on stress distribution, and the influence of glass-based seal depends on the elastic modulus. The simulation results can be applied for optimizing the structural design of the stack and minimizing the high stress concentration in components.

Numerical Inspection based on Quasi-Static Analysis using Rousselier Damage Model for Aluminium Wingbox Aircraft Structure

The present paper illustrates a modelling technique of void damage prediction using constitutive Rousselier damage model in wingbox aircraft structure. The high possibility of aluminium wingbox structure to deform during operating become a driving force in this study. The Rousselier model is implemented by the user-defined material subroutine UMAT in the ABAQUS / Standard. The wingbox is a part of a commercially-made commuter aircraft prototype, in which steady aerodynamic pressure is applied as the quasi-static, ranging from cruise load factor until the ultimate load factor. This analysis is divided into three assessments: load factor assessment, damage detection and implementation of Rousselier-UMAT-XFEM (RuX) model solution. The results indicate the maximum stress concentration occurs at the bottom-root part of the skin. The void volume fraction and the crack grow as the load factor increases to the ultimate load factor. A comparison with the literature is shown in some details.