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The aim of the current research was to investigate the hot tensile behavior and fracture morphology of 410 steel in the temperature range of 950-1100°C and two strain rates of 0.05 s-1 and 0.5 s-1. The results showed that the peak stress and yield stress decreased with increasing temperature, which confirmed the decrease of strength against deformation with increasing process temperature. In strain rate of 0.05 s-1 with increasing temperature, the peak strain decreased continuously, while in strain rate of 0.5 s-1 was observed an increment trend after initial decrease due to competition between work hardening and softening mechanism such as dynamic recovery and dynamic recrystallization. The fracture morphology results showed that they were in good agreement with the mechanical results when at 950°C the brittle fracture mechanism had a high contribution and the soft fracture surface morphology (increasing dimples and decreasing cleavage planes) was dominant with increasing process temperature. At strain rate of 0.05 s-1, the size of the voids and cracks formed during process was much larger than the cracks created at strain rate of 0.5 s-1, which indicated considerable tearing and decrease in fracture strain (elongation) of the samples in during hot tensile testing at low strain rate. [ABSTRACT FROM AUTHOR]

Nowadays, Inconel superalloys are often used in various industries due to their extraordinary properties. Some unique properties of Inconel, such as maintaining its yield strength at elevated temperatures, very low thermal conductivity, and high abrasion resistance, provide very difficult to cut conditions for machining this superalloy. This paper presents a method for simulating the direct aged Inconel 718 superalloy turning by using the power law equation based on the finite element method. One of the main objectives of this research is the correct determination of material properties based on power law equation such as strain hardening coefficients, strain rate sensitivity coefficient, thermal softening coefficients, and other coefficients required to simulate direct aged Inconel 718. The simulation results, such as shear plane angle, machining forces, chip temperature, and tool and chip shape, have been validated by reference [1]. This study, similar to [1], has been studied at three different underformed chip thicknesses to examine the deformed chip thicknesses and other machining outputs such as machining forces using the power law equation. Third wave Systems-AdvantEdge software has been used for the current study. The output of this study has been investigated with the results of experimental research [1] and shows the high efficiency and accuracy of the present analysis. [ABSTRACT FROM AUTHOR]

In this paper, the effect of temperature and bending moments is investigated on the strain accumulation behavior of carbon steel piping branch by using the Chaboche kinematic hardening model with the isotropic hardening law. Carbon steel branch junctions are tested at five temperatures of 20, 50, 100, 150 and 200 ° C under internal pressure and temperature with dynamic bending moment. The results obtained by numerical analysis show that the highest amount of ratcheting occurred near the branch junctions in the circumferential direction. The strain ratcheting occurred mainly because of dynamic moments and high temperatures. The results show that in all three samples, the amount of strain ratcheting increases with increasing of dynamic moment level and temperature. With increasing of the ratio of diameter to thickness in branch junctions, the onset of strain accumulation occurs at low moment levels. It can be concluded that initially, the rate of strain ratcheting is high and with the increase of loading cycles, this rate decreased due to the strain hardening phenomenon. The increase of strain ratcheting at high temperatures is due creep strain because of high temperature and mainly accumulated plastic strain under dynamic bending moments because of cyclic plasticity. [ABSTRACT FROM AUTHOR]

Replacing of conventional concrete by High Performance Fiber Reinforced Cementitious Composite (HPFRCC) could improve tensile strength, bending strength, shear strength and other capability of behaviour such as ductility, energy absorption and toughness. Strain hardening behaviour in (HPFRCC) could result in restrict of crack and prevent from crack widening. Also, because of the high strain capacity of (HPFRCC), using this material in the beam-column connection is more attention paid by researchers. After verification of numerical models for frame using OPENSEES software and comparison with experimental results, two 2D frames with 3 and 6 stories has been created to study. These frames have been designed based on ACI 318. Each frame is considered in 4 formats containing conventional concrete in all elements (RC), containing of (HPFRCC) in beam-column connection (RCH1), containing of (HPFRCC) in beam-column connection and first story column base (RCH2) and containing of (HPFRCC) in all elements. Results from nonlinear static analysis (pushover analysis) show increase of lateral strength, ductility and ultimate displacement of frames containing (HPFRCC) with respect to (RC) frames. Also, using of (HPFRCC) in frames has been decreased maximum story drift ratio, maximum roof displacement and has been increased maximum base shear and story shear in nonlinear time history analysis.

Magnesium and its alloys have received much attention not only in the aerospace and electronics industry, but also in medical applications due to its low density, excellent physical properties, and biocompatibility. However, magnesium and its alloys have low ductility and poor strain hardening ability because of the hexagonal crystal structure with the limited number of slip systems at room temperature. Therefore, it seems necessary to improve their ductility and other mechanical properties via novel technologies. In this research, hydrostatic cyclic expansion extrusion has been used to produce ultrafine-grained magnesium rod. Properties of produced rods have been investigated morphologically and mechanically. The numerical investigation has also been performed to show the effects of hydrostatic pressure on strain distribution. Due to the brittleness of magnesium, the process has been conducted at elevated temperatures. Also, due to the fluid limitation at high temperatures, melted polyethylene has been used as the fluid in the process. The results showed that the yield and ultimate strength increased by 54% and 43% after only one pass of the hydrostatic cyclic expansion extrusion process, respectively. Also, elongation increased by 46%. Furthermore, microhardness has also increased with an average of 57 Hv to 70 Hv. The microstructure result showed that the grains become ultrafine-grained after only one pass of the process. Finite element investigation revealed that high hydrostatic pressure has a good effect on improving the strain distribution and the microstructure. This process seems very appropriate for industrial applications due to its ability to produce long ultrafine-grained rods. [ABSTRACT FROM AUTHOR]

Creep age forming (CAF) process is a novel metal forming method with major benefits including improved mechanical properties and cost reduction for aviation industry applications. CAF happens due to creep phenomenon and stressrelease during the artificial aging of heat-treatable aluminum alloys. In this work, the creep age forming of 7075 Aluminum alloy at 120, 150 and 180 °C for 6, 24 and 48 h was done; tensile and hardness tests were used to characterize the samples. Results on spring-back revealed that it was influenced by time and temperature; by increasing the time and temperature, it was reduced from 54.1 to 39.51. Mechanical property evaluation also showed that by increasing the time, the strength and hardness could be enhanced due to microstructural evolution and precipitation during the CAF process. According to the mechanical and CAF results, two samples were selected as the optimum ones and their work hardening behavior and fracture surfaces were investigated [ABSTRACT FROM AUTHOR]

Among the effects of strain hardening, strain-rate hardening, and temperature softening, it has been long argued about which effect is predominant in governing the material flow stress in machining. In addition, there is a belief that the temperature and strain rate counterbalance the effect of each other therefore there is no need to consider temperature softening and strain-rate hardening while modeling material flow behavior. It means that similar to metal forming processes, the flow stress will be the function of strain only whereas, the magnitudes of strain-rates, and temperatures involved in machining are several orders higher than those generated in forming processes. On the other hand, measuring material flow stress under high strain-rates and temperatures in controllable conditions needs especial costly equipments therefore it is worth to discuss whether the stress-strain data obtained in the simple standard tensile test can be used in machining. This paper discusses some requirements for mathematical form of material models applicable to describe the yield surface in simulation of machining. As a result the first predominant factor governing the material flow stress is strain hardening. It is demonstrated that strain-rate and temperature do not counterbalance the effects of each other in all machining zone. Therefore implemented material model in machining should include both considerable effects in a suitable way. It is demonstrated that friction is an important heat source independent to plastic dissipated energy therefore its contribution in material flow should be considered in convenient method via implementing temperature parameter in mathematical equation of material model. In addition, the velocity of material deformation is another parameter governing the material flow behavior in machining. It is indicated that the strain rate parameter plays the role of suitable corresponding field variable therefore it should be appeared in mathematical form of material model to include related effects.

Strain reversal in the inelastic range may cause a dramatic drop in the tangent modulus for mild steel struts. Other material properties also affect the tangent modulus. Consequently the influence of several of these properties is examined for an electric-resistance welded steel tube. The variables chosen are: (1) Strain hardening caused by varying the amount of tensile prestrain; (2) strain aging; (3) and the Bauschinger effect, for a specific steel type. The results of 39 stub column tests on semi-killed steel specimens show that tensile prestrain reduces the tangent modulus compared with that found for the as-received tube, but strain aging is seen to be significant in reducing this loss in value. The variations obtained for the tangent modulus are illustrated. The variations are given as functions of the amount of tensile prestrain and whether the steel is fully aged or non-aged. The importance of knowledge of prior strain history of a material is highlighted.

In this paper, effect of advanced yield criteria including BBC2003, Yld2004 and BBC2008 are studied using Swift hardening law on determination of limit strains based on Marciniak-- Kuczynski (M-K), Swift's diffuse necking and Hill's localized necking models. These models are used to assess the formability prediction of orthotropic AA2090-T3 and AA6111-T4 sheets. The Portevin-Le Chatelier effect on formability of AA5182-O sheet is also studied. The sensitivity of Marciniak--Kuczynski model to the initial imperfection factor is investigated and the effect of this parameter on prediction of forming limit diagram has been shown. Study of the effect of yield criteria exponent on formability shows the higher exponents which are recommended for FCC metals have higher forming limits in comparison with lower exponents adopted to BCC metals. The effects of strain hardening coefficient and anisotropy are studied too. The results show that the increase of strain hardening exponent improves the formability, while the PLC effect and increase of anisotropy coefficient reduce it. Experimental results show better conformity with M-K model at the right side of FLD and with Hill's localized necking model at its left side. [ABSTRACT FROM AUTHOR]