Location Of Maximum Tensile Stress Research Articles

An ICME framework for short fiber reinforced ceramic matrix composites via direct ink writing

A manufacturing-driven ICME framework is proposed to model short fiber reinforced ceramic matrix composites (CMCs) via direct ink writing. Currently, there lacks efforts to investigate the effects of properties of short fiber reinforced CMCs due to fiber alignment variance. A multi-scale modeling approach is presented to use representative volume elements to capture the homogenized mechanical behavior at various fiber aspect ratios and volume ratios. The orthotropic material properties are mapped to model the printing process. A series of tensile tests simulations show that with 20∘ standard deviation in fiber alignment, the fracture plane has the maximum local tensile stress range at a printing angle of 30∘ and has the minimum local tensile stress range at 90 ∘ . When the standard deviation increases from 20∘ to 40∘, the average tensile strength across the fracture plane decreases by 2%, but the stress variations increase 27.6%.

Surface Roughness-Induced Stress Concentration

When a body is exposed to external forces large local stresses may occur at the surface because of surface roughness. Surface stress concentration is important for many application and in particular for fatigue due to pulsating external forces. For randomly rough surfaces, I calculate the probability distribution of surface stress in response to a uniform external tensile stress with the displacement vector field parallel to the rough surface. I present numerical simulation results for the stress distribution sigma (x,y) and show that in a typical case the maximum local tensile stress may be sim 10 times bigger than the applied stress. I discuss the role of the stress concentration on plastic deformation and surface crack generation and propagation.Graphical

FEM based parametric analysis for investigating effect of wheel base characteristics and axle configurations on flexural stresses in rigid pavements

The main advantages of rigid pavements are their durability and ability to hold their shapes when subject to heavy traffic and extreme weather conditions. Different vehicles have different wheel base characteristics and axle load configurations, due to which the above conditions structurally affect the performance of the rigid pavements in different ways. One of the main causes of critical defects in the rigid pavement is the development of flexural stress exceeding the critical level under different conditions. In rigid pavements the critical stresses are generated with the combination of wheel load stresses and curling stresses. In this paper, the investigation of the variation of flexural stress developed in jointed plain concrete pavements under different axle load configuration and wheelbase characteristics was done using FEM (Finite Element Method). In this paper, the modelling of the rigid pavement was carried out using KENPAVE software. In modelling, effect of both axle load and temperature difference is considered. For loading effect, axle configuration of SASW (Single Axle Single Wheel), SADW (Single Axle Dual Wheel), Tandem and Tridem axle was considered in modelling. To include the combined effect of base and subgrade an equivalent modulus of subgrade reaction was considered as per the IRC-58 code provisions. Parameters related to rigid pavement were taken according to the provisions of IRC code for modelling of base case. Parameters of pavement like thickness of pavement slab, equivalent modulus of subgrade reaction, temperature difference, modulus of elasticity and location of wheel load were changed from the base case and maximum tensile stress was calculated for each axle configurations. Based on the analysis of results for different thickness of pavement slab, equivalent modulus of subgrade reaction, temperature difference, modulus of elasticity and location of wheel load, the variation of magnitude and location of maximum tensile stress was reported for given properties of subgrade, base and axle configuration.

Thermal shock resistance of functionally graded materials with mixed-mode cracks

The thermal shock resistance of functionally graded materials (FGMs) is studied in the presence of periodic mixed-mode cracks as characterization of a typical damaging effect of thermal shock loading on FGMs. A methodology of assessing the thermal shock resistance of FGMs is proposed featuring consideration of both strength and fracture theories. The thermal shock resistance is modeled through three distinct failure criteria: (i) the maximum local tensile stress criterion (ii) the maximum thermal stress intensity factor criterion and (iii) the maximum hoop stress criterion. The finite-difference approximation of the transient temperature field is obtained firstly according to Fourier's law of heat conduction. The corresponding thermal stress field is then obtained through the finite element analysis of the mechanical problem involving thermal strain. With such a coupling between the finite element method (FEM) and finite difference method (FDM) resolving the thermomechanical response, the mixed-mode thermal stress intensity factors (TSIFs) are accordingly extracted through the interaction energy integral method (IEIM). Some typical examples of periodic mixed-mode cracks are presented with the influences of crack spacing, crack length and crack angle on the thermal shock resistance of FGMs studied. Furthermore, the distribution patterns of material properties in FGMs are discussed in terms of their effects on the thermal shock resistance. The results indicate that the proposed methodology provides an effective pathway to assessment of thermal shock resistance of FGMs showing great significance in design and fracture evaluation of such materials.

Stress and damage tolerance analysis of stiffened panel with passenger door cutout in airframe structure using FEA

It is very essential to design the airframe structure with minimum possible weight without compromising on the structural safety. Fuselage has many stress concentration areas. Passenger door cutout region is one among such critical regions. Current work includes stress and damage tolerance analysis of a critical region in the fuselage structure. The structure considered for the analysis includes a stiffened panel with a passenger door cutout and surrounding area with the presence of stiffening members. The present work also includes the damage tolerance analysis of the panel in presence of a crack emanating from the high stress location. The pressurization load case is one of the critical load cases considered for the design of the aircraft structure. The tensile loads at the edge of the panel corresponding to pressurization will be considered for the linear static analysis of the panel. A location of maximum tensile stress and its magnitude will be identified from the stress analysis. Stress intensity factor calculation is carried out for different incremental crack lengths for a crack emanating from the high stress location. Modified virtual crack closure integral method is used for stress intensity factor calculation.

Improving the fatigue performance of porous metallic biomaterials produced by Selective Laser Melting

Additive Manufacturing (AM) techniques such as Selective Laser Melting (SLM) are increasingly being used for producing customized porous metallic biomaterials. These biomaterials are regularly used for biomedical implants and hence a long lifetime is required. In this paper, a set of post-built surface and heat treatments is presented that can be used to significantly improve the fatigue life of porous SLM-Ti6Al4V samples. In addition, a novel and efficient analytical local stress method was developed to accurately quantify the influence of the post-built treatments on the fatigue life. Also numerical simulation techniques were used for validation. The developed methods and techniques can be applied to other types of porous biomaterials and hence provide new and useful tools for improving and predicting the fatigue life of porous biomaterials.

Investigating Stage Construction in High Concrete Arch Dams

Concrete arch dam is a complex geometric structure and designing such a structure requires experience and high knowledge. One of the important parameters in designing concrete arch dams is the tensile stress in arch concrete material. The static analysis results of high arch dam structure depend on structure analysis model, intensively. Stage construction is needed to be focused in modeling high arch dams. In this study, the necessity of considering stage construction in static analysis of dam structure is focused. Modeling stage construction uses Birth and Death technique of elements. Therefore, six stage construction models are provided including applying dam wall weight outright, two stage application including odd and even monoliths, 4-stage application, 8-stage application, 14 stage applications and 24 stage application. The applied structure analysis is finite element method, in this investigation. Increasing construction stages results in decreasing wall cumulative strain energy. Considering 8 and 14 stage constructions results in 2.6% and 1.3% errors in estimating strain energy. Finally, it is clear that considering stage construction results in decreasing maximum tensile stress and changing the location of maximum tensile stress, too. Dam designers can apply the provided methodology.

Thermal shock resistance of solids associated with hyperbolic heat conduction theory

The thermal shock resistance of solids is analysed for a plate subjected to a sudden temperature change under the framework of hyperbolic, non-Fourier heat conduction. The closed form solution for the temperature field and the associated thermal stress are obtained for the plate without cracking. The transient thermal stress intensity factors are obtained through a weight function method. The maximum thermal shock temperature that the plate can sustain without catastrophic failure is obtained according to the two distinct criteria: (i) maximum local tensile stress criterion and (ii) maximum stress intensity factor criterion. The difference between the non-Fourier solutions and the classical Fourier solution is discussed. The traditional Fourier heat conduction considerably overestimates the thermal shock resistance of the solid. This confirms the fact that introduction of the non-Fourier heat conduction model is essential in the evaluation of thermal shock resistance of solids.

Transverse fracture of canine teeth

The critical conditions to effect transverse fracture in canine teeth of carnivores in lateral loading are analyzed. The teeth are modeled as tapered coaxial beams with uniformly thin enamel coats. A stress analysis is first carried out using beam theory, and stress intensity factors for inward propagating cracks at the location of maximum tensile stress along the lingual face are then determined. The fracture begins as arrested channel cracks within the enamel, followed by stable penetration around the tooth and into the dentin to the point of failure. Two- and three-dimensional finite element models are used to evaluate the full fracture evolution. The analysis yields an explicit scaling relation for the critical fracture load in terms of characteristic tooth dimensions, notably tooth height and base radius. The role of enamel, ignored in previous ‘strength of materials’ analyses, is shown to be important in determining the precursor crack equilibrium prior to full fracture. Implications concerning allometry are briefly discussed.

Finite element analysis of a four-unit all-ceramic fixed partial denture

All-ceramic restorations are known to be prone to brittle fracture. However, a previously performed in vitro study indicates that four-unit fixed partial dentures (FPDs) with a zirconia framework are sufficiently strong to withstand occlusal forces in the posterior region. The aim of this study was to determine the stress distribution in such a four-unit FPD made of yttria-stabilized polycrystalline tetragonal zirconia (Y-TZP), under an occlusal load. A three-dimensional finite element model was constructed and a stress analysis performed with a force of 1630 N applied at the centre of the middle connector area. The location of maximum tensile stress according to finite element analysis coincided with the fracture origin of all 10 specimens fractured within the previous in vitro study. The maximum tensile stress in the area of the middle connector amounted to 633 MPa. It increased with the load being applied from the oral towards the buccal side (648 MPa) and decreased with the load being applied from the buccal towards the oral side (570 MPa). These stresses are of the same order as the flexural strength of Y-TZP, determined under standardized test conditions to be 600–1000 MPa. The model presented is intended to be used for further investigations, including thermally induced stresses during veneering.

Point load tests and strength measurements for brittle spheres

A multiaxial failure criterion for brittle materials is applied to a stress field analysis of a perfectly elastic sphere subjected to diametrically opposite normal forces that are uniformly distributed across small areas on the sphere's surface. Expressions are obtained for an intrinsic strength parameter of the material, as well as its unconfined compressive strength. An expression for the unconfined tensile strength is obtained by introducing an additional parameter accounting for the microstructural features of the material. The expressions indicate that failure initiates in the sphere where the ratio between the second deviatoric stress invariant and the first stress invariant is a maximum. Such a criterion does not coincide with the location of maximum tensile stress. The expressions are used to reinterpret published point load test results and predict unconfined compressive strengths. The configuration of the point load test as well as surface roughness and elastic properties of the pointer and samples are taken into account to establish the size of the area on which the point loads act. The predictions are in good agreement with measured values obtained directly using unconfined compressive strength tests. It is concluded that the point load test provides a more reliable estimate of the compressive strength than the tensile strength.

The fracture toughness of planar lattices: Imperfection sensitivity

The imperfection sensitivity of in-plane modulus and fracture toughness is explored for five morphologies of 2D lattice: the isotropic triangular, hexagonal and Kagome lattices, and the orthotropic 0 / 90 ∘ and ± 45 ∘ square lattices. The elastic lattices fail when the maximum local tensile stress at any point attains the tensile strength of the solid. The assumed imperfection comprises a random dispersion of the joint position from that of the perfect lattice. Finite element simulations reveal that the knockdown in stiffness and toughness are sensitive to the type of lattice: the Kagome and square lattices are the most imperfection sensitive. Analytical models are developed for the dependence of modes I and II fracture toughness of the 0 / 90 ∘ and ± 45 ∘ lattices upon relative density. These models explain why the mode II fracture toughness of the 0 / 90 ∘ lattice has an unusual functional dependence upon relative density.

Functionally Graded Materials Under Severe Thermal Environments

Thermal shock strengths of a plate of a functionally graded material (FGM) are analyzed when the plate is suddenly exposed to an environmental medium of different temperature. A finite element/mode superposition method is proposed to solve the time‐dependent temperature field. The admissible temperature jump that the material can sustain is studied using the stress‐based and fracture mechanics‐based criteria. The critical parameters governing the level of the transient thermal stress in the medium are identified. The strength of FGMs under transient thermal stresses is analyzed using both maximum local tensile stress and maximum stress intensity factor criteria.

Thermal Shock Strength of a Semi-infinite Piezoelectric Medium

This paper considers the mechanical problem of a semi-infinite piezoelectric medium under sudden thermal load. The medium contains an electrically conducting crack perpendicular to its surface. The transient stresses and electric fields in an uncracked medium are calculated first. Then, these stresses and electric fields are used as the crack surface traction and electric field loads with opposite signs to formulate the mixed boundary value problem. Numerical results for the stress and electric field intensity factors are calculated as a function of normalized time and crack size. Crack propagation behavior is discussed. The parameters that control the transient thermal stress and electric fields are also identified. The maximum thermal shock strength that the material can sustain without catastrophic failure is established according to two distinct criteria: (i) maximum local tensile stress equals the tensile strength of the medium, and (ii) maximum stress intensity factor for the preexisting representative crack equals the fracture toughness of the medium. The results show that the influence of the piezoelectric effects on the thermal stress intensity factor is insignificant.

Thermal shock resistance of functionally graded materials

Transient temperature field and associated thermal stresses in functionally graded materials (FGMs) are determined by a finite element/finite difference (FE/FD) method. Temperature-dependent material properties are taken into consideration. Explicit expressions for one-dimensional transient thermal conduction in some common elements, such as plate, shell and sphere, are given. These expressions are useful for material engineers and scientists to determine the thermal stresses and strength distributions in FGMs for high temperature applications. Thermal shock fracture of a FGM plate is analyzed when the plate is suddenly exposed to an environmental medium of a different temperature. The admissible temperature jump that the materials can sustain is studied using stress-based and fracture-toughness-based failure criteria. The critical parameters governing the level of the transient thermal stress in the medium are identified. The thermal shock resistance of the FGMs is analyzed using both maximum local tensile stress and maximum stress intensity factor criteria.

Strength Evaluation of Piezoelectric Ceramics under Transient Thermal Environments

The strength of piezoelectric ceramics is analyzed for a plate suddenly exposed to an environmental medium of different temperatures. The admissible temperature jump the material can sustain is studied using the stress- and fracture-toughness-based failure criteria. The critical parameters governing the level of the transient thermal stress in piezoelectric ceramics are identified. Solutions are obtained for the maximum thermal shock that the plate can sustain without failure, under the conditions that (i) maximum local tensile stress equals the tensile strength of the ceramic, and (ii) maximum stress intensity factor for representative pre-existing cracks equals the fracture toughness of the ceramic.

Thermal shock fracture of piezoelectric materials

This paper deals with a case study for the piezoelectric materials suddenly exposed to an environmental medium of different temperature. The problem is idealized to a plate containing an edge crack or an embedded crack. The stress and electric displacement histories in an uncracked plate are calculated. These stresses and electric displacements are then added to the crack surface tractions and electric displacements with opposite sign to formulate a mixed boundary value problem. The cracking problem is thus reduced to a singular integral equation of Cauchy type, which is then solved numerically. Both impermeable crack assumption and permeable crack assumption are considered. The results for stress and electric displacement intensity factors are computed as a function of normalized time and crack size. Lower bound solutions are obtained for the maximum thermal shock that the material can sustain without catastrophic failure according to the two distinct criteria: (i) The maximum local tensile stress equals the tensile strength of the medium. (ii) The maximum stress intensity factor for the pre-existing representative crack equals the fracture toughness of the medium. The parameters that control the transient thermal stress and electric displacement are also identified. The method can be used to explore susceptibility to thermal fracture in piezoelectric materials containing pre-cracks.

The thermal shock resistance of solids

The thermal shock resistance of a brittle solid is analysed for an orthotropic plate suddenly exposed to a convective medium of different temperature. Two types of plate are considered: (i) a plate containing a distribution of flaws such as pores, for which a stress-based fracture criterion is appropriate, and (ii) a plate containing a single dominant crack aligned with the through-thickness direction, for which a critical stress intensity factor criterion is appropriate. First, the temperature and stress histories in the plate are given for the full range of Biot number. For the case of a cold shock, the stress field is tensile near the surface of the plate and gives rise to a mode I stress intensity factor for a pre-existing crack at the surface of the plate. Alternatively, for the case of hot shock, the stress field is tensile at the centre of the plate and gives rise to a mode I stress intensity factor for a pre-existing crack at the centre of the plate. Lower bound solutions are obtained for the maximum thermal shock that the plate can sustain without catastrophic failure according to the two distinct criteria: (i) maximum local tensile stress equals the tensile strength of the solid, and (ii) maximum stress intensity factor for the pre-existing representative crack equals the fracture toughness of the solid. Merit indices of material properties are deduced, and optimal materials are selected on the basis of these criteria, for the case of a high Biot number (high surface heat transfer) and a low Biot number (low surface heat transfer). The relative merit of candidate materials depends upon the magnitude of the Biot number, and upon the choice of failure criterion. The effect of porosity on thermal shock resistance is also explored: it is predicted that the presence of porosity is generally beneficial if the failure is dominated by a pre-existing crack. Finally, the analysis is used to develop merit indices for thermal fatigue.

Normal Wedge Indentation in Rocks with Lateral Confinement

The paper reports results of a numerical analysis of the wedge indentation problem. The main objective of this research is to investigate the influence of the lateral confining stress on the development of the plastic zone under the indenter and on the initiation of tensile fractures. Numerical analysis indicates that the location of maximum tensile stress (interpreted as the point of crack initiation) moves away from the indentation axis as the lateral confinement increases. It is found that a small increase in the confining stress from zero induces a large increase in the inclination of this point on the indentation axis. However, the confinement does not reduce significantly the maximum tensile stress and it hardly influences the indentation pressure. These numerical results shed some light on the mechanism of formation of lateral or sub-horizontal tensile cracks observed in the indentation experiments.

Fracturing at Contact Surfaces Subjected to Normal and Tangential Loads

A variety of rock engineering problems including drilling, cutting, abrasion, and milling involve rock tool contact and indentation. The pattern of indentation fractures and the role of slip conditions, surface roughness, tool radius and initial flaw size for an arbitrarily loaded contact are not fully known. The present paper aims to identify the elastic stress field for a contact subjected to both normal and tangential loads, and evaluate the condition for the fracture initiation and propagation. Stress fields within two spheres at contact are available when either only normal load is applied or when tangential load causes full-slip conditions. It is shown here that through appropriate superposition of the above two solutions, the stress field under partial-slip conditions, as well as during the unloading of tangential force may be determined. Maximum tensile stress increases significantly under partial-slip conditions as compared to the full-slip case even though the same magnitude of tangential force is applied. The location of maximum tensile stress moves inward from the trailing edge as the tangential force is unloaded. The stress-intensity factors for a penny-shaped crack which initiates at the contact periphery, and follows the minimum principal stress trajectory are obtained and utilized to study indentation fracturing. The dependency of critical loads on initial flaw size, indenter radius and slip conditions is quantified. The predictions of fracture density and spacing under a sliding indenter are achieved through a simple estimate of shielding interaction between adjacent fractures. Relation of these evenly spaced fractures with the formation of wear grooves on sliding surfaces is discussed.