Showing papers on "Strain hardening exponent published in 2009"
25 Jan 2009-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the texture and microstructure evolutions of a fine-grained TWIP steel subjected to tensile tests at room temperature were investigated in relation to the mechanical behavior.
Abstract: The texture and microstructure evolutions of a fine-grained TWIP steel subjected to tensile tests at room temperature were investigated in relation to the mechanical behavior. This steel combines both high ductility and strength owing to the TWIP effect. Also the steel exhibits a high strain hardening rate that evolves according to five stages, which are related to the microstructure and texture evolutions and characteristics. The formation of nano-twins in the initial stage of deformation leads to an increase in strain hardening rate. The development of the pronounced fiber in the tensile direction sustains mechanical twinning and maintains the strain hardening rate on a high level. The resulting microstructure exhibits several types of twin configurations and sub-boundaries with high misorientations due to intense activities of dislocation glide. The twin volume fraction was estimated to be 9% at the final stage of tensile deformation. The new orientations generated by mechanical twinning do not change considerably the final texture.
398 citations
TL;DR: In this article, the authors predicted the ductile failure of dual phase steels in the form of plastic strain localization resulting from the incompatible deformation between the harder martensite phase and the softer ferrite matrix.
332 citations
25 Aug 2009-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the authors investigated the tensile properties and work hardening behavior of dual phase (DP) steels with an equal amount of ferrite and martensite.
Abstract: This paper aims to investigate tensile properties and work hardening behavior of dual phase (DP) steels A series of DP steels containing ferrite and martensite with different volume fractions of martensite ( V m ) were produced by intercritical heat treatment Microstructural investigations, hardness test and tensile test were carried out Hardness, yield strength, ultimate tensile strength, ductility and fracture energy were correlated to martensite volume fraction The experimental results showed that dual phase steels with an equal amount of ferrite and martensite have excellent mechanical properties in terms of tensile strength, ductility and fracture energy A further increase in V m was found to decrease tensile strengths and ductility The increasing and then decreasing trend in tensile strength is in contrast to the law of mixture These unusual behaviors are discussed and explained Work hardening behavior was analyzed in terms of Holloman analysis Results showed that in DP steels with less than 50% V m , the work hardening took place in one stage and the work hardening exponent increased with increasing V m By increasing the volume fraction of martensite ( V m > 50%) two work hardening stages were observed in the Hollomon analysis
278 citations
TL;DR: In this paper, the self-healing behavior of a series of pre-cracked fiber reinforced strain hardening composites incorporating blast furnace slag and limestone powder with relatively high water/binder ratio is investigated, focusing on the recovery of its deflection capacity.
Abstract: The self-healing behavior of a series of pre-cracked fiber reinforced strain hardening cementitious composites incorporating blast furnace slag (BFS) and limestone powder (LP) with relatively high water/binder ratio is investigated in this paper, focusing on the recovery of its deflection capacity. Four-point bending tests are used to precrack the beam at 28 days. For specimens submerged in water the deflection capacity can recover about 65-105% from virgin specimens, which is significantly higher compared with specimens cured in air. Similar conclusion applies to the stiffness recovery in water cured specimens. The observations under ESEM and XEDS confirmed that the microcracks in the specimens submerged in water were healed with significant amount of calcium carbonate, very likely due to the continuous hydration of cementitious materials. The self-healing cementitious composites developed in this research can potentially reduce or even eliminate the maintenance needs of civil infrastructure, especially when repeatable high deformation capacity is desirable, e.g. bridge deck link slabs and jointless pavements. © 2009 Elsevier Ltd. All rights reserved.
263 citations
TL;DR: In this paper, the cyclic deformation behavior and low cycle fatigue (LCF) of a large solid extruded section of AZ31 magnesium alloy was investigated. And the authors observed that the alloy was cyclically stable at lower strain amplitude and exhibited cyclic hardening characteristics at higher strain amplitude, with a cyclic hardness exponent of about 2.6 times higher than the monotonic strain hardening exponent.
237 citations
TL;DR: In this paper, a non-associated flow rule (NAFR) model is proposed to improve the accuracy of springback, tearing, and earing predictions for aluminum and stainless steel alloys.
214 citations
15 Dec 2009-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, a modified Crussard-Jaoul (C-J) analysis and microstructural observations were used to investigate the strain hardening behavior of a Fe-18Mn-0.6C-1.5Al TWIP steel.
Abstract: The strain hardening behavior of a Fe–18Mn–0.6C–1.5Al TWIP steel was investigated through the modified Crussard–Jaoul (C–J) analysis and microstructural observations. The strain hardening rate obtained by modified C–J analysis was high up to the critical strain of 37% and then greatly decreased with further strain. The electron backscatter diffraction (EBSD) observation showed that the deformation twinning rate is greatly decreased beyond about 34% strain, indicating that the reduced strain hardening rate at the large strain region is attributed to the deceleration of deformation twinning rate. The volume fraction of twinned region was increased with tensile strain due to the increase in the number of deformation twins not to the lateral growth of each deformation twin.
212 citations
TL;DR: In this article, the stress-strain behavior of extruded AA6xxx and AA7xxx aluminium alloys in T6 temper was studied at a wide range of strain rates, and the experimental data were used to identify the parameters of a thermo-viscoplastic constitutive relation for the extruded alloys.
197 citations
TL;DR: In this paper, a hierarchical multiscale modeling methodology involving two distinct bridges over three different length scales is proposed to predict the work hardening of face centered cubic crystals in the absence of physical experiments.
189 citations
TL;DR: In this paper, the elastic and plastic properties of high-strength steels with multiple phases were characterized using the in situ high-energy X-ray diffraction technique, where the authors provided a fundamental understanding of the stress partitioning of soft and hard phases, and the different workhardening rates of the multiphase steels.
188 citations
TL;DR: In this article, the differential speed rolling (DSR) with a roll speed ratio of 1.167 was carried out on an AZ31B magnesium alloy in order to investigate its effects on the formability.
TL;DR: In this paper, a new explanation for the stress-strain behavior of austenitic TWIP steels (or other low stacking-fault alloys deforming by twinning) is presented, emphasizing the key contribution of the reinforcement of the thin (nanometric) deformation twins both to the macroscopic strain hardening and to the development of forward and backward internal stresses in respectively twin and matrix regions.
15 May 2009-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the tensile properties of a DP 600 and a TRIP 700 steel were characterized by tensile tests over a temperature range of −100 ǫ −100 t −100 T −235 T at strain rates ranging from 10−3 to 1250 s−1, showing that the strain hardening behavior of the TRIP steel depends strongly on the initial test temperature, to which the DP steel seems to be relatively insensitive in the studied temperature interval.
Abstract: The dependence of the mechanical behavior of DP and TRIP steels on temperature and strain rate is still not completely understood. Therefore, the mechanical properties of a DP 600 and a TRIP 700 steel were characterized by tensile tests over a temperature range of −100 ≤ T ≤ 235 °C at strain rates ranging from 10−3 to 1250 s−1. The results show that the strain hardening behavior of the TRIP steel depends strongly on the initial test temperature, to which the DP steel seems to be relatively insensitive in the studied temperature interval. On the other hand, the tensile strength of the TRIP steel appears to be much less sensitive to strain rate than that of the DP steel. This is explained by the effects of deformation induced heating on the martensite transformation based hardening of the TRIP steel, partially offsetting the direct effects of strain rate.
TL;DR: In this paper, a viscoplastic crystal plasticity model is incorporated within the Marciniak-Kuczynski (M-K) approach for forming limit curve prediction, allowing for the incorporation of crystallographic texture-induced anisotropy and the evolution of the same.
TL;DR: In this paper, a friction welding process was attempted to join titanium (Ti) to 304L stainless steel (SS) for the dissolution of spent fuel that is carried out in boiling nitric acid in the dissolver vessel (made of Ti) and the dissolved solution is transported through the 304L SS pipes to the other plant components made of 304 l SS.
TL;DR: In this paper, an elasto-plastic constitutive model for frozen sandy soil is developed based on the continuum damage theory, the cross anisotropic damage variables are deduced and their change regularities are investigated.
TL;DR: Strong strain hardening in NC nickel with a grain size of approximately 20 nm under large plastic strains is shown, contrary to common belief, and significant dislocation accumulation in the grain interior is observed.
Abstract: Low strain hardening has hitherto been considered an intrinsic behavior for most nanocrystalline (NC) metals, due to their perceived inability to accumulate dislocations. In this Letter, we show strong strain hardening in NC nickel with a grain size of approximately 20 nm under large plastic strains. Contrary to common belief, we have observed significant dislocation accumulation in the grain interior. This is enabled primarily by Lomer-Cottrell locks, which pin the lock-forming dislocations and obstruct dislocation motion. These observations may help with developing strong and ductile NC metals and alloys.
TL;DR: In this paper, the effects of addition of different types of sands of different contents on the strain hardening behavior of hybrid fiber composites are evaluated. And the authors found that the addition of sand adversely affected the tensile strain hardness and multiple cracking behaviour of hybrid fibre composites.
TL;DR: In this article, a servo-hydraulic type high speed tensile testing machine was used to obtain stress-strain curves of mild steel and advanced high strength steels at strain rates ranged from 1/sec to 200/sec.
Abstract: This paper presents stress-strain curves of steel sheets for an auto-body obtained at intermediate strain rates with a servo-hydraulic type high speed tensile testing machine. The apparatus has the maximum stroke velocity of 7.8 m/sec to obtain the tensile material properties at a strain rate of up to 500/sec. A special jig fixture is specially designed for accurate acquisition of tensile loads with reduction of the load-ringing phenomenon induced by unstable stress wave propagation at high strain rates. Tensile testing of steel sheets for an auto-body was carried out to obtain stress-strain curves of mild steel and advanced high strength steels at strain rates ranged from 1/sec to 200/sec. The test results provide interesting information regarding the stress-strain curves at intermediate strain rates ranged from 1/sec to 200/sec and demonstrate that strain rate hardening is strongly coupled with strain hardening.
TL;DR: In this article, the work hardening of a model Al-3Cu-0.05Sn (wt.%) alloy containing shear-resistant θ ′ (Al 2 Cu) precipitate plates was studied as a function of precipitate state.
20 Aug 2009-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the influence of strain ratio and strain rate on cyclic deformation characteristics and fatigue life of an AZ31 extruded alloy was investigated. And the residual twins acting as barriers to dislocation slip and pile-up were considered to be the main cause for the occurrence of cyclic hardening.
Abstract: Magnesium alloys are increasingly used in automotive and aerospace industries for weight reduction and fuel economy improvement. Low cycle fatigue (LCF) behavior of these alloys is an important consideration for the structural applications. The objective of the present investigation was to identify influences of strain ratio and strain rate on cyclic deformation characteristics and fatigue life of an AZ31 extruded alloy. As the strain ratio decreased, stronger cyclic hardening rate, more asymmetric hysteresis loop, smaller stress amplitude, lower mean stress, and higher initial plastic strain amplitude were observed due to increasing compressive stresses. This was considered to be associated with the twinning during cyclic deformation in the compressive phase, and detwinning in the tensile phase. The residual twins acting as barriers to dislocation slip and pile-up were considered to be the main cause for the occurrence of cyclic hardening. Fatigue life increased with decreasing strain ratio and increasing strain rate. Fatigue crack initiation occurred at the specimen surface due to the presence of larger grains near the surface, and fatigue crack propagation was characterized by a mixture of striations and dimple-like ductile fracture features.
TL;DR: In this article, the initial and subsequent yield surfaces in Al 6061-T6511 were determined during tension, free end torsion, and combined tension-torsion proportional loading paths after reaching different levels of strains.
TL;DR: In this paper, the rate dependence of fracture has been studied in a series of physically associating triblock copolymer gels that have a well-defined molecular structure, and compressive experiments were performed to develop a strain energy function that accurately captures the strain hardening behavior of these materials.
Abstract: The rate dependence of fracture has been studied in a series of physically associating triblock copolymer gels that have a well-defined molecular structure. Compressive experiments were performed to develop a strain energy function that accurately captures the strain hardening behavior of these materials. This same strain energy function was utilized in a finite element model of the crack tip stresses, which become highly anisotropic at stress values below the failure strength of the gels. The rate dependence of the energy release rate, G, is independent of the gel concentration when G is normalized by the small strain Young's modulus, E. The gels exhibit a transition from rough, slow crack propagation to smooth, fast crack propagation for a well-defined value of the characteristic length, G/E.
TL;DR: In this paper, the anisotropic effects on the microstructure and mechanical response of rolled magnesium alloy Mg-3Al-1Zn in the H24 condition have been quantified.
TL;DR: In this paper, a single-crystal face-centered cubic metal pillars synthesized using a focused ion beam are reported to be stronger when compressed in smaller volumes, and it is shown that plastic deformation is initially controlled by the boundary constraints of microcompression tests, followed by classical crystal plasticity for uniaxial compression.
TL;DR: In this paper, a 3D constitutive model is proposed to capture both the conventional shape memory effects of pseudoelasticity and thermal strain recovery, and additionally considers the initiation and evolution of plastic strains.
Abstract: The new developments summarized in this work represent both theoretical and experimental investigations of the effects of plastic strain generation in shape memory alloys (SMAs). Based on the results of SMA experimental characterization described in the literature and additional testing described in this work, a new 3D constitutive model is proposed. This phenomenological model captures both the conventional shape memory effects of pseudoelasticity and thermal strain recovery, and additionally considers the initiation and evolution of plastic strains. The model is numerically implemented in a finite element framework using a return mapping algorithm to solve the constitutive equations at each material point. This combination of theory and implementation is unique in its ability to capture the simultaneous evolution of recoverable transformation strains and irrecoverable plastic strains. The consideration of isotropic and kinematic plastic hardening allows the derivation of a theoretical framework capturing the interactions between irrecoverable plastic strain and recoverable strain due to martensitic transformation. Further, the numerical integration of the constitutive equations is formulated such that objectivity is maintained for SMA structures undergoing moderate strains and large displacements. The implemented model has been used to perform 3D analysis of SMA structural components under uniaxial and bending loads, including a case of local buckling behavior. Experimentally validated results considering simultaneous transformation and plasticity in a bending member are provided, illustrating the predictive accuracy of the model and its implementation.
TL;DR: In this paper, two flours were used in this study, one from the wheat variety Jagger (Jagger) and the other from a composite of soft wheat varieties (Soft).
TL;DR: In this article, the authors extended the Marciniak-Kuczynski (MK) forming limit model to predict localized necking in sheet metal forming operations in which Through-Thickness Shear (TTS), also known as out-of-plane shear, occurs.
TL;DR: In this paper, a fine-grained single-phase Mg-Zn-Al alloy (AZ31) was shown to have superplastic behavior with an elongation to failure ratio of 475% at 1 × 10−4 s−1 and non-superplastic behaviour with a deformation ratio of 160%, and the corresponding strain rate sensitivities were 0.5 and 0.2, respectively.
TL;DR: In this paper, the size-dependent deformation behavior of Niobium single-crystalline samples 200-900 nm in diameter was investigated by in situcompression and tension testing.