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21 – 30 of over 2000Yue Wang, Dan Wang, Meng Zhao, Fei Xie and Kaili Zhang
The purpose of this study is to find the multi-factor influence law of stress, strain rate and sulfate-reducing bacteria (SRB) on X70 pipeline steel in a simulated solution of sea…
Abstract
Purpose
The purpose of this study is to find the multi-factor influence law of stress, strain rate and sulfate-reducing bacteria (SRB) on X70 pipeline steel in a simulated solution of sea mud and the order of influence of the three factors on X70 steel to develop a scientific basis for pipeline corrosion protection.
Design/methodology/approach
This paper studied the effects of stress, strain rate and SRB on the X70 pipeline steel corrosion behavior in simulated sea mud solution through orthogonal testing, electrochemical experiments and morphological observations.
Findings
The results of this study showed that stress proved to be the most relevant element for corrosion behavior, followed by SRB and strain rate. At high stresses (301 MPa and 576 MPa), stress dominated the corrosion behavior of X70 pipeline steel. However, at low stress (82 MPa), SRB played the most important role.
Originality/value
Subsea pipelines are in a very complex environmental regime that includes stress, strain rates and SRB, which often cause pipeline pitting and perforation. However, most scholars have only looked into the influence of single factors on metal corrosion. So, the single-factor experimental results of previous studies could hardly be applied to actual working conditions. There is an urgent need to understand the multi-factor influence law of stress, strain and SRB acting together on the pipeline corrosion behavior, especially to determine the dominant factor.
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Kei Kimura, Takeshi Onogi and Fuminobu Ozaki
This work examines the effects of strain rate on the effective yield strength of high-strength steel at elevated temperatures, through tensile coupon tests at various strain…
Abstract
Purpose
This work examines the effects of strain rate on the effective yield strength of high-strength steel at elevated temperatures, through tensile coupon tests at various strain rates, to propose appropriate reduction factors considering the strain rate effect.
Design/methodology/approach
The stress–strain relationships of 385 N/mm2, 440 N/mm2 and 630 N/mm2-class steel plates at elevated temperatures are examined at three strain rate values (0.3%/min, 3.0%/min and 7.5%/min), and the reduction factors for the effective yield strength at elevated temperatures are evaluated from the results. A differential evolution-based optimization is used to produce the reduction-factor curves.
Findings
The strain rate effect enhances with an increase in the standard design value of the yield point. The effective yield strength and standard design value of the yield point exhibit high linearity between 600 and 700 °C. In addition to effectively evaluating the test results, the proposed reduction-factor curves can also help determine the ultimate strength of a steel member at collapse.
Originality/value
The novelty of this study is the quantitative evaluation of the relationship between the standard design value of yield point at ambient temperature and the strain-rate effect at elevated temperatures. It has been observed that the effect of the strain rate at elevated temperatures increases with the increase in the standard design value of the yield point for various steel strength grades.
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Lakhwinder Singh, Sangyul Ha, Sanjay Vohra and Manu Sharma
Modeling of material behavior by physically or microstructure-based models helps in understanding the relationships between its properties and microstructure. However, the…
Abstract
Purpose
Modeling of material behavior by physically or microstructure-based models helps in understanding the relationships between its properties and microstructure. However, the majority of the numerical investigations on the prediction of the deformation behavior of AA2024 alloy are limited to the use of phenomenological or empirical constitutive models, which fail to take into account the actual microscopic-level mechanisms (i.e. crystallographic slip) causing plastic deformation. In order to achieve accurate predictions, the microstructure-based constitutive models involving the underlying physical deformation mechanisms are more reliable. Therefore, the aim of this work is to predict the mechanical response of AA2024-T3 alloy subjected to uniaxial tension at different strain rates, using a dislocation density-based crystal plasticity model in conjunction with computational homogenization.
Design/methodology/approach
A dislocation density-based crystal plasticity (CP) model along with computational homogenization is presented here for predicting the mechanical behavior of aluminium alloy AA2024-T3 under uniaxial tension at different strain rates. A representative volume element (RVE) containing 400 grains subjected to periodic boundary conditions has been used for simulations. The effect of mesh discretization on the mechanical response is investigated by considering different meshing resolutions for the RVE. Material parameters of the CP model have been calibrated by fitting the experimental data. Along with the CP model, Johnson–Cook (JC) model is also used for examining the stress-strain behavior of the alloy at various strain rates. Validation of the predictions of CP and JC models is done with the experimental results where the CP model has more accurately captured the deformation behavior of the aluminium alloy.
Findings
The CP model is able to predict the mechanical response of AA2024-T3 alloy over a wide range of strain rates with a single set of material parameters. Furthermore, it is observed that the inhomogeneity in stress-strain fields at the grain level is linked to both the orientation of the grains as well as their interactions with one another. The flow and hardening rule parameters influencing the stress-strain curve and capturing the strain rate dependency are also identified.
Originality/value
Computational homogenization-based CP modeling and simulation of deformation behavior of polycrystalline alloy AA2024-T3 alloy at various strain rates is not available in the literature. Therefore, the present computational homogenization-based CP model can be used for predicting the deformation behavior of AA2024-T3 alloy more accurately at both micro and macro scales, under different strain rates.
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Kei Kimura, Takeshi Onogi, Naoya Yotsumoto and Fuminobu Ozaki
In this study, the effects of strain rate on the bending strength of full-scale wide-flange steel beams have been examined at elevated temperatures. Both full-scale loaded heating…
Abstract
Purpose
In this study, the effects of strain rate on the bending strength of full-scale wide-flange steel beams have been examined at elevated temperatures. Both full-scale loaded heating tests under steady-state conditions and in-plane numerical analysis using a beam element have been employed.
Design/methodology/approach
The load–deformation relationships in 385 N/mm2-class steel beam specimens was examined using steady-state tests at two loading rate values (0.05 and 1.00 kN/s) and at two constant member temperatures (600 and 700 °C). Furthermore, the stress–strain relationships considering the strain rate effects were proposed based on tensile coupon test results under various strain rate values. The in-plane elastoplastic numerical analysis was conducted considering the strain rate effect.
Findings
The experimental test results of the full-scale steel beam specimens confirmed that the bending strength increased with increase in strain rate. In addition, the analytical results agreed relatively well with the test results, and both strain and strain rate behaviours of a heated steel member, which were difficult to evaluate from the test results, could be quantified numerically.
Originality/value
The novelty of this study is the quantification of the strain rate effect on the bending strength of steel beams at elevated temperatures. The results clarify that the load–deformation relationship of steel beams could be evaluated by using in-plane analysis using the tensile coupon test results. The numerical simulation method can increase the accuracy of evaluation of the actual behaviour of steel members in case of fire.
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J.N. Pires, F.J. Caramelo, P. Brito, J. Santos and M.F. Botelho
Implant surgery is generally accepted as the best technique for complete teeth replacement. However, it is also the most demanding technique to implement and the most onerous to…
Abstract
Purpose
Implant surgery is generally accepted as the best technique for complete teeth replacement. However, it is also the most demanding technique to implement and the most onerous to the client. It would be helpful to reduce costs and simplify procedures in order that the general public could benefit from implant dentistry. This paper reports a robotic system developed with the objective of studying stress/strain distribution caused by implants inserted in blocks of a polymer. The polymer exhibits the same mechanical properties of the human mandible bone.
Design/methodology/approach
The system includes an industrial robot manipulator, a data acquisition board, strain gauges for stress/strain evaluation and a force/torque sensor (equipped with accelerometers) placed on the robot wrist. The objective is to optimize the number of implants and their placement/orientation, contributing in this way to reduce the overall cost of implant surgery. The system is presented in detail and explored for drilling and implant insertion.
Findings
The preliminary results are encouraging and indicate the usefulness of the system. The three presented situations correspond to general clinical procedures and, as can be concluded from the preliminary results, the intensity of the applied forces increase with the inclination of the drilling tool. Since, the depth of the holes is the same, it can be also concluded that the dissipated energy is superior in the 30° hole. Apart from inclination all the other properties remain constant during the force evaluation; therefore, we expected that during the perforation of the 30° hole the temperature should raise more than in the other types of holes. This aspect will be addressed in detail in the near future (just by carefully monitoring the temperature) because living tissues should not be submitted to temperatures greater than 42°C. The observed fluctuation in the modulus of the force during a drilling cycle suggests that the material is not homogeny. The results indicate that the strain is larger in the vertical load. This might be related with the fact that inclined applied forces imply a distribution of the strain/stress forces at least for two directions.
Research limitations/implications
Further work will include more sensors to obtain all the data.
Practical implications
This will be of interest to the implant industry, since low prices will significantly increase the market and consequently the need for implant products. Currently, implant surgery as well as teeth replacements are based on a few general rules that, very often, do not take into account the specific needs of the patient. This happens independently of clinician expertise, which does not have enough biomechanical information to plan the number, location and orientation of implants in a specific surgery. Consequently, in most of the cases the needs are overestimated, to guarantee long‐term success, which implies expensive procedures and more discomfort for patients.
Originality/value
This work reports on a robotic system to simplify implant procedures.
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The purpose of this paper is to develop the method for the calculation of residual stress and enduring deformation of helical springs.
Abstract
Purpose
The purpose of this paper is to develop the method for the calculation of residual stress and enduring deformation of helical springs.
Design/methodology/approach
For helical compression or tension springs, a spring wire is twisted. In the first case, the torsion of the straight bar with the circular cross-section is investigated, and, for derivations, the StVenant’s hypothesis is presumed. Analogously, for the torsion helical springs, the wire is in the state of flexure. In the second case, the bending of the straight bar with the rectangular cross-section is studied and the method is based on Bernoulli’s hypothesis.
Findings
For both cases (compression/tension of torsion helical spring), the closed-form solutions are based on the hyperbolic and on the Ramberg–Osgood material laws.
Research limitations/implications
The method is based on the deformational formulation of plasticity theory and common kinematic hypotheses.
Practical implications
The advantage of the discovered closed-form solutions is their applicability for the calculation of spring length or spring twist angle loss and residual stresses on the wire after the pre-setting process without the necessity of complicated finite-element solutions.
Social implications
The formulas are intended for practical evaluation of necessary parameters for optimal pre-setting processes of compression and torsion helical springs.
Originality/value
Because of the discovery of closed-form solutions and analytical formulas for the pre-setting process, the numerical analysis is not necessary. The analytical solution facilitates the proper evaluation of the plastic flow in torsion, compression and bending springs and improves the manufacturing of industrial components.
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The paper reports experiments carried out on beams in pure bending. The material used was a cast magnesium alloy AZ855. The beam sections were rectangular, circular, I‐section…
Abstract
The paper reports experiments carried out on beams in pure bending. The material used was a cast magnesium alloy AZ855. The beam sections were rectangular, circular, I‐section, T‐scction and diamond. One series of tests was carried out up to 1 per cent fibre strain. A second series of tests was carried out up to fracture. Tension and compression tests were also made on the material. The experimental results show conclusively that the usual theory of plastic bending is correct and that the tension‐compression stress‐strain curve of the material may be used to determine the bending moment‐curvature relationships, etc., for a beam. Measurements of neutral axis shift also confirm the predictions of plastic bending theory.
Jason Martinez and Ann Jeffers
A methodology for producing an elevated-temperature tension stiffening model is presented.
Abstract
Purpose
A methodology for producing an elevated-temperature tension stiffening model is presented.
Design/methodology/approach
The energy-based stress–strain model of plain concrete developed by Bažant and Oh (1983) was extended to the elevated-temperature domain by developing an analytical formulation for the temperature-dependence of the fracture energy Gf. Then, an elevated-temperature tension stiffening model was developed based on the modification of the proposed elevated-temperature tension softening model.
Findings
The proposed tension stiffening model can be used to predict the response of composite floor slabs exposed to fire with great accuracy, provided that the global parameters TS and Kres are adequately calibrated against global structural response data.
Originality/value
In a finite element analysis of reinforced concrete, a tension stiffening model is required as input for concrete to account for actions such as bond slip and tension stiffening. However, an elevated-temperature tension stiffening model does not exist in the research literature. An approach for developing an elevated-temperature tension stiffening model is presented.
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Huawu Liu and Warren G. Bryson
Using the stress-strain relationship of wool cells, a three-component model (cuticle, ortho-, and para-/mesocortex) was developed to model the bending properties and behaviour of…
Abstract
Using the stress-strain relationship of wool cells, a three-component model (cuticle, ortho-, and para-/mesocortex) was developed to model the bending properties and behaviour of the wool. The bending rigidity varied with not only the elastic moduli and geometry, but also the direction of the applied moment, whereas bending stiffness is insensitive to the direction of the load. The simulations indicated that the cuticle might contribute 25% of the bending stiffness in extreme cases and should not be ignored, as has been the case in previous studies.
Single fibre curvature (SFC), as a particular bending behaviour associated with the removal of moisture, was illustrated using finite element analysis. The physical properties of the three components (cuticle, ortho-, and para-/mesocortex) of Romney wool fibres are estimated using the stress-strain relationship models. The geometric configuration of the samples is built from true fibre images. The simulations are validated to be qualitatively consistent with the observations of SFC. The displacement, stress and strain energy of the wool fibre due to moisture desorption are mapped using coloured figures.
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The purpose of this paper is to compare mechanical response of polypropylene in multi‐cycle tensile tests with strain‐controlled and mixed deformation programs and to develop…
Abstract
Purpose
The purpose of this paper is to compare mechanical response of polypropylene in multi‐cycle tensile tests with strain‐controlled and mixed deformation programs and to develop constitutive equations that describe quantitatively the experimental data.
Design/methodology/approach
Multi‐cycle tensile tests are performed on isotactic polypropylene with strain‐controlled (oscillations between fixed maximum and minimum strains) and mixed (oscillations between a fixed maximum strain and the zero minimum stress) programs. A constitutive model is derived in cyclic viscoelasticity and viscoplasticity of semicrystalline polymers, and its parameters are found by fitting observations. The effect of damage accumulation of material parameters is analyzed numerically.
Findings
The model predicts accurately mechanical behavior of polypropylene in tests with numbers of cycles strongly exceeding those used to determine its parameters. In the regime of developed damage, material constants in the stress‐strain relations are independent of deformation program.
Originality/value
A novel constitutive model is derived in cyclic viscoelastoplasticity of semicrystalline polymers and comparison of its adjustable parameters is performed for different deformation programs.
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