Numerical Stress Analysis Research Articles

Biaxial flexural failure of woven composite plates investigated by the ring on ring bending test

Abstract The ring on ring (ROR) bending test is an ASTM standard (C1499) for characterizing the equibiaxial flexural strength of ceramics. This simple test protocol induces biaxial flexure by applying an out of plane uniaxial load via a small loading ring, to a plate or disc shaped specimen, simply supported on a larger ring. The main objective of this paper is to apply this test method to analyze the biaxial flexural failure of woven fabric composite plates. Ring on ring bending tests are conducted on square shaped plate specimens of epoxy/carbon plain woven composites, until failure. Experiments reveal interesting similarities and differences when compared to ceramics. First it is seen that while for ceramics the bottom surface fractures under biaxial tension, for woven composites the top surface fractures under biaxial compression. The failure pattern however, is similar to ceramics, and consists of several radial kink bands which initiate near the center and propagate outwards towards the specimen edges. Subsequent numerical stress analysis of the test reveals that the stress state in the region of the plate encompassed by the loading ring is almost exactly equibiaxial. This is primarily because the test method induces pure bending and because the two in-plane principal moduli are equal to each other, and much larger than all the other moduli. This implies near axisymmetry of the stress state despite material orthotropy. This aspect is seen to enable a simple determination of the biaxial flexural strength using the in-situ measured principal strains. It also implies that this biaxial flexural strength could be a good approximation of the equibiaxial compressive strength for the woven composite, directly measuring which is usually a challenging task. Conditions for the suitability of this test method are explored via further numerical modeling.

A semi-analytical stress correction method for bi-material Mode-III V-notches

This article proposes a method to correct the numerical near singularity stress field in vicinity of reentrant corners by a semi-analytical solution. The approach pertains to perfectly bonded bi-material interface V-notches with arbitrary opening angles under Mode-III loading. The method addresses dissimilar joints with sharp corners in large-scale numerical engineering models where high-resolution discretization becomes computationally expensive. The method is therefore particularly useful for fatigue lifetime analysis of shear-bending dominated large utility multi material structures such as compound castings, aircraft wings and wind turbine rotor blades to name a few. The solution for the governing Laplace equation is obtained by separation of variables in conjunction with the eigenvalue expansion method yielding the bi-material notch singularity exponent. The notch stress intensity factor is then used to fit the analytical singular near field to the numerical far field utilizing the fact that the latter is more accurately predicted. The analytical anti-plane shear stress correction method is valid for any geometry subject to arbitrary remote loading conditions. The accuracy of the approach is investigated by numerical stress analysis of a slender beam subject to axial torsion for different notch opening angles.

Numerical analysis of moisture-induced strains and stresses in glued-laminated timber

Abstract Changes in relative humidity of the ambient air, RH (%), cause wetting and drying of wood material, which results in non-uniform moisture contents or moisture gradients, and consequently in moisture-induced stresses and strains in the glued-laminated timber (glulam) members. The aim of the present paper is to perform a hygro-mechanical analysis to predict the mechanical behavior of glulam specimens exposed to two RH regimes, causing wetting from 50% to 90% RH and drying from 90% to 50% RH, and compare the numerical to the experimental results. The aims are also to quantitatively analyze the influence of characteristic material parameters required in the multi-Fickian moisture transport model and the mechanical model on moisture-induced strains and stresses in glulam specimens and to determine the possibility of cracking of the material by analyzing the maximum tensile stresses perpendicular to the grain. Accurate numerical predictions of moisture contents and moisture-induced strains are obtained in the glulam specimens during wetting and drying as compared to the experimental results. The influence of a particular characteristic material parameter on moisture-induced strains and stresses is characterized as significant, but not crucial when a rough numerical estimation of the mechanical behavior of the glulam beam exposed to RH changes is required.

Numerical Analysis of Stress Causing Fracture Failure in the Gear Transmission System Applied on an Agricultural Machinery Equipment

In general, failures often occur in gear transmission systems, even this case also occurs in an agricultural machinery equipment for example in a hand tractor. This study aimed to determine the cause of the spur gear fracture through numerical studies. The fracture surface was observed using a scanning electron microscope (SEM) in order to identify crack initiation. The results of the chemical composition test indicated that the material used was according to the AISI 8620 standard. It is necessary to create a finite element analysis (FEA) modeling. The stress, strain and stress intensity factor was next analysed near the crack tip using the FEA. The results of the FEA pointed out that the value of the maximum stress intensity factor KI occurs in the center of the tooth which experiences an initial crack due to friction. The KI value obtained from the FEA indicates that the value is higher than the fracture toughness KIC. Finally, crack propagation occurs in the teeth of the spur gear that causes the tractor to stop working.

Elastoplastic Axisymmetric Deformation of Shells Under Thermomechanical Loading and Radiation*

A method for numerical analysis of the thermoelastoplastic axisymmetric stress–strain state of thin isotropic shells undergoing mechanical loading and radiation exposure is outlined. The modified constitutive equations of thermoplasticity describing inelastic deformation along small-curvature paths are employed. The thermoelastoplastic state of a shell in the form of a spherical segment is analyzed numerically with allowance for the effect of radiation.

Numerical analysis of residual stresses on microscale and mesoscale in hot bulk forming parts under specific cooling

AbstractThe adjustment of targeted residual stress states is important in order to improve the properties of a component. Here, especially hot forming processes offer a meaningful potential since a number of parameters such as deformation state, temperature profile or cooling media can be adapted independently. This publication presents first simulation steps for the calculation of residual stresses on microscale and mesoscale. As a first application, the microscopic phase transformation from austenite to martensite due to a cooling process is considered. The arising mesoscopic eigenstrain distributions are used in the solution of an elasto‐plastic two‐scale boundary value problem to gain resulting residual stress states.

Numerical analysis of ground displacement and segmental stress and influence of yaw excavation loadings for a curved shield tunnel

This paper describes the key influences of yaw excavation loadings on ground displacement and segmental stress for a curved shield tunnel. The influences are investigated through finite element models, the reliabilities of which are validated through comparisons to field data and analytical solutions. Multiple case studies of different curvature tunnels and their comparison to straight-line tunnels are presented. Under the dual action of overcutting and construction loadings, the surface settlement of the curved tunnel is larger than that of the straight-line tunnel. The horizontal displacements at the inner and outer sides of the curved tunnel are asymmetric with respect to the tunnel axis. This asymmetry can increase significantly during yaw excavation of over one ring width. Yaw excavation loadings have a significant influence on the horizontal and vertical displacements of the ground within a span of shield length starting from the position of the hydraulic jacks until the back. The circumferential compressive stress, axial tensile stress, and axial compressive stress of newly installed segment of the curved tunnel are greater than those of the straight-line tunnel. Interestingly, the stress increments increase linearly with yaw severity. The results are of benefit to suggest improvements for practical construction procedures.

Experimental and Numerical Study of the Formation of Thermophysical Characteristics of Carbon Composite Materials. Part 2. Numerical Simulation of Operability of a Refractory Product Made of Carbon Composite Material

A heating of a carbon-made product and thermophysical properties of a carbon material in the temperature range from 300 to 2,500 K were studied. A discrete-heterogeneous mechanism of heating the surface of a multi-dimensionally reinforced carbon-carbon composite material (CCCM) subject to accelerated heating was revealed. Based on the results of testing carbon materials in the temperature range from 300 to 3,000 K, a numerical stress analysis of the product was performed, in which the arising stress condition was considered to be resultant from constraining the deformation of the heated parts of the product by relatively cold fragments. The safety factor levels were found for different parts of the product. It was shown that an additional increase in thermal strength as part of the combined definition of thermal resistance of CCCM products is associated with high thermal conductivity of 1D-reinforced rods of material structure.

Viscoplastic modelling of HDPE geomembrane local stresses and strains

The formulation, validation and application of a viscoplastic constitutive model for numerical analysis of HDPE geomembrane stresses and strains induced by overlying coarse gravel is presented. Model parameters were obtained from uniaxial tensile experiments conducted over a range of displacement rates. The model was implemented in geometrically-nonlinear finite-element-analysis and was able to match the force, displacement and strain measured from wide-width strip tensile experiments. The analysis also matched the geomembrane response measured from axisymmetric force-displacement experiments, where a 60-mm-diam. specimen, clamped around its perimeter, was subjected to loading normal to its plane from a steel probe machined to mimic the shape of a coarse gravel particle. The analysis matched: i) probe forces when loaded at a constant rate of displacement, ii) displacements when loaded with step function increments of probe force, iii) creep displacements under a constant probe force for 1000 h, and iv) decreases in probe force from stress relaxation when held at a constant displacement for 1000 h. The analysis was used to further validate the applicability of thin plate theory to calculate geomembrane strains from measured deformations and provide first estimates of stress that develop beneath a gravel particle.

Predicting fatigue crack propagation in residual stress field due to welding by meshless local Petrov-Galerkin method

This paper introduces a novel procedure to develop the MLPG method for investigating residual stress effect on the Fatigue Crack Propagation (FCP) rate. A new formulation is introduced based on thermoelastic-plastic equation for this method to numerical analysis of the residual stress due to welding. The most important part of numerical analysis by MLPG method is to determine the residual stress redistribution due to crack growth and calculation of the Stress Intensity Factor (SIF) in residual stress field. A good agreement is seen between the outputs of MLPG method to the Hole-Drilling Strain-Gage method results. The standard weight function is developed without increasing the computational time for simulation of the displacement and stress around the crack. The Superposition principle is employed to consider the residual stress effect on the SIF and cycle ratio. Finally, the Walker’s FCP equation is modified to take into account the simultaneous effects of cyclic loading and residual stress. It was discovered that the results obtained from the purposed method is in a good agreement with FCP experimental results. Therefore, it can be concluded a new approach is developed to analyze the calculation of SIF in the residual stress field and its effect on the FCP rate.

Evaluation of Penetration Depth for Cutoff Walls in the Core of Earth Dams

Seepage and water flow into soil are of the critical factors in the design of earth dams. There are various methods to control seepage in the dam foundation. One solution is the use of plastic concrete cutoff wall. Due to a higher hydraulic gradient in the union area and pressure increase of embankment above the wall by time, a considerable consolidation occurs in the wall. Therefore, crack in the wall, water seepage and erosion in the union area may occur. Hence, one of the items considered in earth the dams sealing system of design especially for plastic concrete cutoff walls is union area. This paper focuses on the effects of penetration depth of cutoff walls into the core of earth dams. To this aim, Anbaran dam located in the north-west of Iran was selected as a case study. Various penetration depths of cutoff walls including 0, 1, 2 and 3 m were considered. A two-dimensional model was defined and the results were compared together. For the numerical modeling and analysis of stresses and displacements in the mode of statics, including the construction stage and the first impoundment stage, GeoStudio-2007 and FLAC2D softwares were used, and for the dynamic stage FLAC2D was used. The results show that the penetration depth of wall plays an effective role in the flow rate of water, hydraulic gradient, stress and displacement of wall and union area. The results of numerical model revealed that, as the penetration depth increases, stresses and displacements of union area increase while the hydraulic gradient and seepage at the union area decrease. Finally, by analyzing the dam behaviorial parameters such as stress, displacement, seepage and hydraulic gradient, and also considering the economic and implementation aspects, the penetration depth of 2 m is chosen as an optimum penetration depth of this case. In this state, the maximum magnitudes of vertical and horizontal stresses are 2371 kPa and 728 kPa, respectively and the maximum magnitudes of vertical and horizontal displacements are 19.36 cm and 7.42 cm, respectively. The amount of seepage under the dam body is 3.330 × 10−6 m3/s/m and the maximum hydraulic gradient in the wall is 39.222. However, to find an optimum penetration depth of cutoff wall into the clay core, numerical analysis with corresponding specifications are strictly needed, indeed.

The application of the meshless local Petrov-Galerkin method for the analysis of heat conduction and residual stress due to welding

The structural analysis of welding based on the thermal-elastic-plastic finite element method can lead to acceptable accuracy for the short time of welding. But if the welding time is long and the thermal source is moving, problems arise in the analysis due to the mesh re-generation. In this paper, in order to overcome the weak points of the finite element method, the meshless local Petrov-Galerkin (MLPG) method by using moving least square (MLS) has been used, based on the weak solution of equations governing the temperature field and the residual stress caused by welding. Without increasing the computational time, accuracy of the MLPG method has increased by developing this numerical method by taking into account the influence of MLPG parameters. To investigate the distance and density of nodal distribution, the relation between support domain size and quadrature domain size with distance between nodes is optimized. A good agreement is seen between the outputs of this numerical method to the hole-drilling strain-gauge method results. Therefore, it can be concluded that a new application based on thermoelastic-plastic equation for the MLPG method to numerical analysis of the residual stress due to welding is introduced.

Numerical Analysis of Lattice Structures for Skin Layer in Camber Morphing Wing

Unlike conventional fixed wings and their static skin structure considering only expected aerodynamic loadings while filight, design strategies of skin structure for morphing wings require careful consideration of structural loading from shape changes and aerodynamics and their coupled effects in flight. Many morphing wings often overlook skin material and structure for the wing design. In addition to that, many works in the design of skins for morphing wings typically use smart materials, consider only geometric or static analysis but not dynamic deformation and strengths, or suggest a material condition and its properties that satisfy required structural and aerodynamic conditions. This work is focused on numerical analysis of structural and aerodynamic stress and strain of various lattice structures that will suggest desired design criteria of skin in camber morphing wings in the future. As a result, this paper shows numerical analysis of various lattice structures in accordance with camber moprhing and their potential effectiveness for skin of morphing wings.

Numerical stress analysis in adhesive joints under thermo-mechanical load using model with special boundary conditions

A numerical study of the adhesivejoint made of similar and dissimilar adherends subjected to thermo-mechanical loading is presented. A comprehensive numerical model was used for this purpose with the novel displacement coupling conditions which are able to correctly represent monoclinic materials (off-axis layers of composite laminates). The geometrical nonlinearity as well as nonlinear material model are also taken into account. Three different types of single-lap and double-lap adhesive joints are considered in this study: a) metal-metal; b) composite-composite; c) composite-metal. In case of composite laminates, four lay-ups are evaluated: uni-directional ([08]T and [908]T) and quasi-isotropic laminates ([0/45/90/-45]S and [90/45/0/-45]S). This paper focuses on the parameters which have the majoreffect on the peel and shear stress distribution within adhesive layer at the overlap ends. The comparison of behaviour of single-and double-lap joints in relation to these parameters is made. The master curves for maximum stress (peel and shear) at the ends of the overlap with respect to the bending stiffness and axial modulus of the adherends are constructed by analysing stress distributions in the middle of the adhesive.The main conclusions of this paper are: the maximum peel stress value for SLJ is reduced with increase of the adherend bending stiffness and for DLJ,similar behaviour was observed at the end next to the inner plate corner, while, at the end next to the outer plate corner peel stress is reduced with increase of adherend axial modulus.

Manufacturing method for high-amplitude corrugated thin-walled laminates

Manufacturing of corrugated carbon-fiber reinforced composite laminates based on circular segments poses a challenge if high corrugation amplitudes create undercuts. This paper suggests to leave the formation of such high-amplitude corrugation shapes to thermal deformation of flat lay-ups which is effected by the difference between curing and service temperatures. It is shown by simulations that the method works best for carbon fibers of moderate stiffness and toughened epoxy-resin systems with high curing temperatures. Simple methods for predicting resulting shapes and stress distributions are explained and they verify non-linear structural simulations with FEM. A manufactured demonstrator validates the results. In addition to pointing out the new manufacturing method, some attention is paid to the potential application of corrugated laminates as flexible skins in morphing wings. It is pointed out how easily the morphing sections can be integrated into the manufacturing of wing skin and numerical stress analyses underline the strength feasibility of the manufacturing method. It comes as an additional benefit of the suggested manufacturing method that sliding overlaps can be integrated to create an aerodynamically smooth surface.

The improvement of stress correction in post-necking tension of cylindrical specimen

In post-necking tension of cylindrical specimen, the stress corrections based on the current analytical models have relatively significant errors at large strains. In this study, the prediction capability of these models involving Bridgman model, Siebel model and Chen model is evaluated by performing a series of finite element simulations of uniaxial tension of cylindrical specimen with different hardening exponents varied from 0.05 to 0.3. Numerical analysis of stress and strain distributions on the necking cross section indicates that the considerable errors of the corrected stresses corresponding to large strains might be mainly attributed to the assumption of uniform strain distribution on the necking cross section in these analytical models. The modification strategies of these models are presented in order to improve their prediction accuracy of post-necking stresses, taking geometrical configuration of neck and material properties into consideration. Accordingly, the modification formulas are proposed based on simulation results, involving the radius of cross section of neck and the hardening exponent. Finally, these formulas are used to correct the stresses in the post-necking tension of Q345 cylindrical specimen, which are compared with the stresses identified through inverse method. The results indicate that the modified models significantly improve the prediction accuracy of post-necking stresses at large strains.

Failure analysis study of railway draw-hook coupler

Failure analysis of railway draw-hook coupler was carried out. The nondestructive testing method was undertaken on some failed couplers in service to designate critical areas of a coupler. Draw-Hook coupler is used to connect with the same hook coupler or automatic coupler. The influence of each connection types on the coupler strength in this study was discussed. A numerical stress analysis using FEM was performed, and many approaches including critical plane approach were carried out on fatigue life prediction of coupler under different conditions. The results of the proposed fatigue criterion and fatigue life predictions, as well as static numerical analysis, are validated with experimental results.

Analysis of the Pressure Expansion of Bridge Plug Tools and Packers by Equivalent Material Method

For the bridge plug tool and packer, the pressure expansion process and differential pressure loading process of the bridge plug and packer have been simulated by finite element method. The numerical structural stress analysis of the bridge plug and the packer are carried out, and the structure of the bell mouth of the cartridge assembly is optimized. The results show that the replacement of the laminated steel structure in the bridge plug/packer with equivalent materials can greatly improve the calculation efficiency, thus completely calculating the pressure expansion and differential pressure loading of the bridge/packer. After the bridge plug/packer expands, the excessive stress is concentrated at the bell mouth. The optimized structure of the elliptical curve at the bell mouth has relatively low stress. This calculation provides theoretical support for the sealing and optimization of bridge plugs and packers.

Numerical Analysis of the Deterministic Stresses Associated to Impeller-Tongue Interactions in a Single Volute Centrifugal Pump

In this paper, a deterministic stress decomposition is applied over the numerical three-dimensional flow solution available for a single volute centrifugal pump. The numerical model has proven in previous publications its robustness to obtain the impeller to volute-tongue flow interaction, and it is now used as starting point for the current research. The main objective has been oriented toward a detailed analysis of the lack of uniformity in the flow that the volute tongue promotes on the blade-to-blade axisymmetric pattern. Through this analysis, the fluctuation field may be retrieved and main interaction sources have been pinpointed. The results obtained with the deterministic analysis become of paramount interest to understand the different flow features found in a typical centrifugal pump as a function of the flow rate. Moreover, this postprocessing tool provides an economic and easy procedure for designers to compare the different deterministic terms, also giving relevant information on the unresolved turbulence intensity scales. Complementarily, a way to model the turbulent effects in a systematic way is also presented, comparing their impact on the performance with respect to deterministic sources in a useful framework, that may be applied for similar kinds of pumps.

Numerical analysis of interlaminar stresses in open-hole laminates under compression

In this paper, the interlaminar stresses in open-hole laminates subjected to compressive loads are analysed using a numerical model. This model implements the Serial/Parallel Mixing Theory (S/PMT) and a Continuum Damage Mechanics (CDM) approach. The S/PMT estimates the global stiffness in the laminate from fibre and matrix properties. The CDM approach models the damage initiation due to fibre microbuckling. The global response estimated by the model was verified with experimental data from the literature. The model predicts that the damage initiates in the laminate middle-plane where the thickest block of plies oriented in the load direction is located, and progressively propagates to the nearest block of layers with the same orientation. Two laminate stacking sequences were analysed. The interlaminar stresses around the hole presented symmetry with respect to the load direction and the perpendicular axis, being located the maximum and minimum values in different angular positions for each stress component and laminate.