Dimensional Finite Element Simulations Research Articles

Stress distribution model for the entire plastic zone of conical indentation with power-law hardening materials

<p indent="0mm">The classical contact mechanics provides an elastic conical indentation solution, and verifies that the strain field of elastic-plastic indentation with an arbitrary blunt indenter mostly satisfies the expanding cavity model. This study reviews the stress solution of the elastic zone for conical indentation using power-law hardening materials derived from predecessors based on the expanding cavity model and elastic-plastic mechanics. Furthermore, the expression of von-Mises equivalent stress in the plastic zone of conical indentation is determined according to the plastic stress solution of an internally pressurized thick spherical shell. The numerical verification revealed that the calculated equivalent stresses via finite element analysis are consistent with the theoretical solution of the elastic zone for conical indentation. However, a clear deviation in the entire plastic zone for the power-law hardening materials is still observed. Furthermore, to accurately describe the equivalent stress in the entire plastic zone of conical indentation for power-law hardening materials, a novel model for the indented stress distribution is established by combining the dimensional analysis method and finite element simulation. Finally, the stress model was verified using a wide range of ductile materials. The comparison results revealed that all of the calculated equivalent stresses are consistent with the model predictions for the entire plastic zone.

A feasibility study on high-efficient laser cutting of SiC particles reinforced aluminum matrix composite using single-pass strategy

Conventional machining of particles reinforced metal matrix composite (PRMMC) is very challenging due to the uniform distribution of abrasive reinforced SiC particles, which easily causes machined surface scratches and severe tool wear. The rapid development of high-power fiber laser has made it possible to cut PRMMCs with high efficiency. In this work, high-power fiber laser was employed to cut 5.0 mm thick SiC particle reinforced aluminum (SiCp/Al) composites. The effects of laser power, cutting speed and assist gas pressure on surface morphology and defect characteristics were investigated. The statistical analysis was conducted to investigate interaction between cutting parameters and kerf geometry. A high-resolution confocal laser scanning microscope was used to further analyze machined surface morphology and microscopic defects. Thermal defects were highly related to cutting parameters, which included cataphracted dross, droplet dross, craters, apophyses, microcracks and combustion. Microcracks were prevalent mainly due to the difference in thermal properties between reinforcement and matrix materials. Three dimensional finite element simulation of two-phase SiCp/Al composites was carried out to predict the temperature and stress distribution, and the striation formation mechanisms were further explained. A new method for predicting thermal stress of SiCp/Al composites was proposed and subsequently compared/validated with experimental results.

Three dimensional extended finite element simulation of cracked functionally graded pipe and pipe bend

In this work, extended finite element method (XFEM) is used to simulate the fracture mechanics problems of part-through semi-elliptical circumferential crack in functionally graded pipe and pipe bend. Part-through semi-elliptical circumferential crack present in functionally graded pipe and pipe bend at different location has been subjected to internal pressure. Higher order shape function is used to model the crack with level set functions. The inner surface of the functionally graded pipe/pipe bend contains 100% steel alloy and outer surface contains 100% alumina ceramic. The material property gradation is followed by exponential law from inner surface to outer surface of the pipe and pipe bend in radial direction. Domain-based interaction integral approach has been used to determine the stress intensity factor at different location of the crack front.

A Three – Dimensional Finite Element Analysis of Polyetheretherketone PEEK in Dental Implant Prosthesis: A Novel Implant System

Purpose: This current numerical investigation aim to evaluate the benefits of substituting Titanium with CRF- PEEK for better stress distribution in implant- bone interface. Methods: 3D models of a dental implant for the first mandibular molar were constructed using the computed tomography (CT) scan. Four distinct models using a combination of titanium, carbon reinforced polyetheretherketone (CRF- PEEK), and zirconia for implant /abutment materials were studied. A three- dimensional finite element simulation was used to evaluate the stress distribution at the implant – bone interface under a compressive axial load of magnitude 120 N. A spherical indenter was used to simulate occlusal load. Results: Mesh independent study was converged for a very large number of elements. Finite element analysis showed: 1) there was no significant difference in the distribution pattern of stress at the implant – bone interface in the different material models studied, 2) the stress values for all prosthetic implant parts were well below the yield strength, 3) a larger deformation of PEEK implant versus titanium. Conclusion: The substitution of titanium with PEEK for the implant does not provide any better stress distribution and may lead to problems from the deformation of the implant.

Finite element analysis of the Non-Equal Channel Angular Pressing (NECAP) with different die geometries

The Non Equal Channel Angular Pressing is one of the promising severe plastic deformation techniques which is used to produce ultra-fine grained and nanostructured materials. In the present investigation, the deformation behavior of Al1100 alloy during non-equal channel angular pressing was studied using two dimensional finite element simulation. Results showed when the ratio of the width of output to input channel is higher than 0.7, the corner gap is formed in the outer side of the intersecting area of two channels and the amount of plastic strain decreases in the lower part of the sample. In contrast, when the amount of this ratio is lower than 0.7, the dead metal zone is formed in the outer region of the intersecting area and the amount of strain is increased in the lower side of sample. It is also observed that the uniformity of the applied plastic strain is decreased with the formation of dead metal zone. In addition, the amount of damage factor is increased with increasing the ratio of the width of output to input channel and the region with higher amounts of damage factor is shifted from the lower side to the middle region of deformed sample. Finally, the results of FEM simulation showed that the amount of pressing force is decreased with increasing the width of output channel.

Theoretical model for determining elastic modulus of ceramic materials by nanoindentation

In order to accurately determine the mechanical properties of ceramic materials with small size specimens by the nanoindentation experiment, an effective work ratio of indentation method is proposed based on the dimensional analysis and finite element simulation to extract elastic modulus of ceramic materials from sharp indentation load-displacement data. Results indicate that the influence of strain hardening exponent of materials on elastic modulus is very weak and can be ignored in this model. Moreover, the elastic modulus of the investigated material can be expressed as a simple function of the work ratio of indentation, plane strain elastic modulus of the indenter, as well as the nominal hardness of the investigated material. Additionally, the effectiveness and accuracy of this proposed method were verified by instrumented indentation tests on two typical certified standard fused silica and borosilicate crown glass samples with Berkovich indenter. After comparison with conventional Oliver-Pharr method, it is shown that the work ratio of indentation method has advantages including high accuracy and small standard deviation.Graphical abstract [Display omitted]

Damage Propagation Prediction of Adhesion Failure in Composite T-joint Structure and Improvement using PZT Patch

In this paper, a three dimensional finite element simulation model has been developed for the prediction, propagation and improvement of adhesion failure in an adhesively bonded laminated T-joint structure using the smart piezoelectric material. Initially, the three-dimensional stresses (normal and shear) and failure locations in the composite T-joint (all the layers of the web and flange) are evaluated. At the identified failure location, virtual crack closure technique (VCCT) of fracture mechanics has been employed to compute the strain energy release rate (SERR) values for different pre-embedded adhesion failure lengths. The developed coupling analysis model is used to evaluate the SERR responses for the laminated composite T-joint with single/multiple piezoelectric layers. The efficacy and improved performance (resistance to adhesion failure) of the laminated smart T-joint structure have been analysed in details by considering the different influencing parameters i.e. orientation schemes, material types, piezoelectric layers, thickness, number of layers of the laminate.

Feedback stabilization of forming processes

We develop online feedback control for forming processes governed by nonlinear material models. A novel approach based on a description using partial differential equation governing time-dependent viscoplastic deformations is proposed. The derivation of the feedback control law is based on a Lyapunov analysis of the linearised partial differential equation. Analytically and in the spatially one-dimensional setting exponential decay of the time evolution of perturbations to desired stress–strain states is established. Also, a similar performance of the feedback control is observed when implemented in a three–dimensional finite element simulation of titanium alloy forming.

Three-dimensional fracture analysis for a thin cracked hardening plate

A semi-analytical method is presented to investigate fracture behavior of a mode-I crack in a thin ductile plate. In the part of theoretical analysis, a total deformation theory of plasticity, in conjunction with a power law hardening stress-strain relation, is employed. Three-dimensional Maxwell stress functions, the minimum complementary potential energy principle and three dimensional J-integrals are used to obtain crack front stress fields. In the part of numerical analysis, three dimensional finite element simulations are carried out to obtain J-integrals, the out-of-plane constraint level and crack front stress fields. Comparison with numerical results of crack front stress fields shows the analytic solutions for crack front stress fields are valid. Numerical and analytic results show that the value of the opening stress ahead of the crack front deceases with increasing z (approaching the free surface) and lies between the corresponding plane strain and plane stress solutions.

Three dimensional finite element simulations of hydraulic fracture height growth in layered formations using a coupled hydro-mechanical model

In this paper, we treat the important problem of hydraulic fracturing in the presence of elastic modulus and stress contrast in layered rock systems encountered in petroleum resources development using a fully coupled 3D hydro-mechanical model. First, the model is validated by simulating a laboratory hydraulic fracturing experiment dealing with the influence of stress contrast. Good agreements in the distribution of fracture aperture, injection pressure and fracture footprint have been achieved. Then, numerical analyses are performed to investigate the influence of in-situ stress and formation layer properties, such as Young's modulus and fracture energy release rate on the height growth and containment of hydraulic fractures. Comparing the results of simulations using conventional thickness-weighted Young's modulus to those from explicit modeling of layers' Young's moduli, it is found given that for the same amount of injection volume, the thickness-weighted modulus generates a higher injection pressure. Explicit modeling of the layers influences the hydraulic fracture aperture distribution in the pay zone as well as in the surrounding layers. A relatively large fracture aperture is observed in the layer with the lower Young's modulus. Also, the hydraulic fracture tends to propagates mainly in the lower Young's modulus layers which could facilitate containment of the hydraulic fracture by limiting height growth in the stiffer layers. When considering the influence of stress contrast on height growth, the conventional equilibrium height model produces a relatively large aperture and overestimates the fracture height. Simulations using typical injection rate, fluid viscosity, and in-situ stress, show stress contrast larger than a certain value, for example 30% of the in-situ minimum horizontal stress, can effectively inhibit height growth. When the payzone is bounded by ductile layers, the injection pressure is higher and the corresponding aperture at the injection point is larger than those obtained using uniform rock properties.

Characterization on the yield stress and interfacial coefficient of friction of glasses from scratch tests

Based on dimensional analysis and finite element simulation, a new method is proposed to characterize the yield stress and interfacial coefficient of friction of materials by scratching with a Vickers indenter. Two simple equations are obtained: one is for determining the interfacial coefficient of friction between the scratched material and scratch tip via the ratio of tangential to normal force, and the other is for calculating the yield stress of scratched material with the groove width and normal force. In a case study, the method is applied to soda-lime and borosilicate glasses. It is shown that the measured results of yield stress and interfacial coefficient of friction between glasses and a diamond tip are consistent with that obtained by other methods, with a high accuracy. The quick and accurate determination of yield stress and interfacial friction coefficient provides important information for the design and processing of glass products.

Reliability Assessment on Stability of Slopes Reinforced with Anti-sliding Piles in Spatially Variable Soils

A reliability-based analysis method considering spatial variability of soil properties was proposed for stability analysis of pile-reinforced slope system in this paper. A total of 71 three dimensional (3D) finite element simulation results were used to develop a Polynomial Regression (PR) model relating the safety factor (FOS) of the slope system to the key input parameters. The PR model was proved to be reasonably accurate with a high coefficient of determination. It was subsequently implemented into a modified spreadsheet involving First-order reliability method (FORM) and spatial variability factors to perform spatial variability and reliability analyses. Based on the results, some useful conclusions are arrived with regard to the effects of spatial variability factors. In addition, a useful guideline for geotechnical engineers to choose suitable pile locations in engineering practices is provided.

Measurement and evaluation on contact stress at the rubber contact interface

Based on the measurement principle of the ultrasonic method, the prediction and evaluation of the contact stress at the rubber contact interface are experimentally and numerically studied in this paper. First, the relationship between the ultrasonic echo signal and the interface contact stress is calibrated based on the ultrasonic method. Second, both the propagation and the interface reflection of ultrasonic at the rubber interface under different displacements are simulated using the finite element method, and the effects of the contact stress and the interfacial roughness on the ultrasonic propagation are analysed. Finally, the empirical fitting formula of ultrasonic reflection coefficient at the rubber interface between rubber and different materials is established by considering the damping, the thickness, the contact stress and the interfacial roughness through dimensional analysis method and finite element simulation, which is well validated by the experiment.

Three Dimensional Finite Element Simulation of Strip Shape and Flatness of High Strength Steel

High-strength steel is a type of alloy steel that provides better mechanical properties or greater resistance to corrosion than carbon steel. Strip shape is an important factor affecting the strip quality significantly for the rolled products. Because of the complex influence factors of plate shape and profile, shape detection and control technology have not been solved, especially for high strength steel rolling. In this paper, a novel three dimensional finite element simulation of the strip shape and flatness of high strength steel has been proposed. The material constitutive model has been built up based on experimental results through the Gleeble 3800 Thermal Simulator under different temperatures and stain rates. The modelling of roll elastic deformation system, roll gap profile and edge drop has been set up systematically considering the influence of the work roll transverse shifting and roll bending. Results have shown that both higher bending force and more roll shifting will significantly reduce the strip crown, and obtain improved edge drop distribution as well. The proposed numerical model has been validated through hot rolling experiments in 4-high rolling mills.

Quasi static compression behavior of glass filled epoxy composites

The effect of filler volume fraction on the quasi-static compression behaviour of low volume fraction glass filled epoxy composites is demonstrated by plotting the stress vs. strain curves for the filler reinforced composites. The results indicate negligible influence of spherical particles on the yield and post yield behaviour of composites due to the large inter-particle separation distance at low volume fractions. To get more insight into the influence of filler shape on the deformation mechanisms, a computational study is performed where a set of inclusions surrounded by the epoxy matrix is modeled and the materials’ deformation response to the compressive loading is analyzed by conducting a two dimensional elasto-plastic finite element simulations. From this analysis, it is revealed that the compressive stresses in the fillers are not affected with increase in the filler volume fraction; but the Mises stresses in the matrix increases with the increase in the filler volume fraction in the hardening regime of the plastic flow curve.

Roll Pass Design and Simulation on Continuous Rolling of Alloy Steel Round Bar

Reasonable design of roll pass schedule is the prerequisite for a successful shape rolling process. In this paper three dimensional elastoplastic finite element simulation with thermal mechanically coupled analysis is applied to study the roll pass design of the hot continuous rolling of Ф100mm alloy steel round bar from 200mm×200mm square cast bloom. Due to the larger plastic strain occurring at the corner of the workpiece, the method of bias meshing for the cross section is adopted to fine the elements of surface and corner area. The stress, strain, temperature distribution, rolling force and rolling moment of the hot continuous rolling are simulated to analyze the plastic deformation and the position and cause of possible rolling defects in order to confirm the roll pass design. The simulated results of cross section sizes of rolled steel at the exit of each pass are in good agreement with the measured values.

An accelerometer balance for aerodynamic force measurements over Hypervelocity Ballistic models in shock tunnel

A force balance to measure drag, lift and pitching moment over Hypervelocity Ballistic (HB) models 1 and 2 has been developed and assessed in an impulse test facility, hypersonic shock tunnel. The experiments were carried out at different angles of incidence of the models with the freestream at nominal Mach numbers of 5.78 and 8.31. The force balance is provided with rubber supports to ensure unrestrained motion of the model during the hypersonic freestream flow. Three dimensional finite element simulations are carried out to assess the performance of the force balance system in measuring the acceleration within the short test duration available in the shock tunnel. The force balance is mounted inside the model and is equipped with accelerometers to sense the model’s acceleration in the desired direction. The aerodynamic force and moment coefficients are then deduced from the measured acceleration signals based on theories in aerodynamics. The measured values of force and moment coefficients match well with the theoretical values estimated using modified Newtonian theory for HB 1 and HB 2 models. In addition, CFD simulations are carried out for the experimental test cases using viscous, laminar models and the numerically computed force coefficients are validated by comparing against the experimental values. The present study demonstrates the use of accelerometer based force balance for measuring aerodynamic forces and moments over realistic long missile configurations.

Prediction and optimization of load and torque in ring rolling process through development of artificial neural network and evolutionary algorithms

Developing artificial neural network (ANN), a model to make a correct prediction of required force and torque in ring rolling process is developed for the first time. Moreover, an optimal state of process for specific range of input parameters is obtained using Genetic Algorithm (GA) and Particle Swarm Optimization (PSO) methods. Radii of main roll and mandrel, rotational speed of main roll, pressing velocity of mandrel and blank size are considered as input parameters. Furthermore, the required load and torque in ring rolling process are taken into account as process outputs. Various three dimensional finite element simulations are performed for different sets of process variables to achieve preliminary data for training and validation of the neural network. Besides, the finite element model is approved via comparison with the experimental results of the other investigators. The Back Propagation (BP) algorithm is considered to develop Levenberg–Marquardt feed-forward network. Additionally, Model responses analysis is carried out to improve the understanding of the behavior of the ANN model. It is concluded that results of ANN predictions have an appropriate conformity with those from simulation and experiments. Moreover, GA and PSO methods have been implemented to obtain the optimal state of process while their outcomes have been also compared.

Optical properties of silver nanoplates and perspectives for biomedical applications

Silver nanoplates of triangular shapes have attractive optical extinction spectrum with multipolar resonance modes. In this work, we investigate the optical properties of Ag nanotriangles and evaluate the feasibility of using it on LSPR biosensing and on photodynamic therapy. Three dimensional finite element simulation and experimental analyses were explored on the assessment of the LSPR spectrum and spatial distribution of the electromagnetic field enhancement near metallic nanoplates, with different altitude length and thickness. Refractive index based sensitivity (406 nm/RIU) and figure of merit (2.6) values were measured for AgNPls colloids, and attributed to dipole LSPR near field enhancement at the tips of the nanostructure. It was observed that LSPR field enhancement extend for more than 18 nm from the nanoparticle surface, indicating the viability of using the nanoplates on molecular sensing. The interaction of Ag nanoplates with Methylene Blue photosensitizer was also appraised, and a 2.2–fold metal enhanced single oxygen generation was determined. Our results indicate that Ag nanotriangles are promising candidates for biosensing and photodynamic application.

Temperature assessment when milling AISI D2 cold work die steel using tool-chip thermocouple, implanted thermocouple and finite element simulation

Due to the cyclic mechanical and thermal loads imposed to the cutting tool during milling, the study of the process temperature is of utmost importance for the better understanding of various associated phenomena, such as tool life and wear mechanisms, cutting forces behavior and workpiece subsurface metallurgical alterations. Nevertheless, temperature measurement during milling operations imposes a number of restraints to experimental methods, mostly related to the cutter rotational speed, variable chip thickness and intermittent action of the cutting edges. The principal goal of this work is to perform a comparative study of the cutting temperature during in end milling using implanted and tool-chip thermocouple methods under distinct operating parameters. Additionally, finite element simulation is employed to correlate the results provided by the experimental techniques. Tool-chip thermocouple and implanted thermocouple experimental methods were used in addition to three dimensional finite element simulation. The findings indicated that the developed system is capable to cope with the drawbacks associated with intermittent machining operations and to provide reliable temperature values for both experimental methods. Milling temperature increased with cutting speed, feed per tooth and both axial and radial depths of cut, however, the relevance of each factor varied in accordance with the measurement method. The average cutting temperature was not statistically affected by cutting direction and the experimental determination of the friction coefficient between tool and workpiece was critical to the accurate temperature determination using three dimensional numerical simulation.