Monotonic Torsion Research Articles

Strain path dependent dynamic recrystallization and its resulted material flow and microstructure evolution of a titanium alloy

Changing strain path is an effective method to optimize the hot working process and improve microstructure and mechanical performance of titanium alloys. In this work, dynamic recrystallization (DRX) and its resulted material flow and microstructural behaviors in monotonic torsion (MT) and forward-reverse torsion (FRT) were comparatively explored by experimental and crystal plastic finite element simulation methods. The results indicate that both MT and FRT can induce discontinuous DRX (DDRX) and continuous DRX (CDRX). However, compared to MT where CDRX always prevails, FRT makes DDRX more important since it inhibits CDRX by recovering the lattice rotation during the reversal stage. Moreover, in FRT, the driving force and the grain boundary content for DDRX nucleation and bulging are relatively low at a small total strain. And the recovery of lattice rotation in FRT can also suppress CDRX. Therefore, DRX kinetics is obviously delayed at a smaller strain. As strain increases, both the stored energy for DDRX and the long-range misorientation gradient for CDRX are gradually greater, thus improve DRX kinetics. With these effects by DRX, although FRT exhibits a lower grain refinement degree at a smaller total strain compared to MT, it can make grain refinement degree rapidly rise and even close to that in MT at a greater strain. Also, FRT can obviously weaken the deformation texture by inducing extensive DDRX grains and recovering the lattice rotation of retained grains. In addition, the texture formed in forward stage and DRX delaying can result in a decrease in yield strength and softening rate in reversal stage, respectively, i.e., exhibiting remarkable Bauschinger effect, especially at a higher forward strain. These results can provide a basic guidance for designing the hot working process of titanium alloys to obtaining more refined microstructure and excellent properties of the components.

Effect of artificial aging time on torsional fatigue life and cyclic behavior of AA6351 aluminum alloy and evaluation of estimation methods

AbstractThe effects of artificial‐aging time on monotonic properties and torsional fatigue of AA6351 aluminum alloy were studied in this paper. Fatigue tests were carried out by the strain‐controlled condition. Monotonic and cyclic torsional behavior, fatigue life, and estimation methods were verified. Results showed the distance between monotonic and cyclic curves progressively decreased as aging time increased from 1 to 2 and 6 h at 170°C. The yield strength values were subsequently 74.5, 110.7, and 142.5 MPa for monotonic torsion and 127, 145, and 160 MPa for cyclic torsion test (half‐life). Alloy in all aging times showed similar fatigue life in high cycle (N f > 105 cycles), and time 1 h, longer fatigue life in low cycle (Nf < 104 cycles). All specimens presented cyclic hardening at strain amplitudes ranges tested. The estimation methods showed good prediction for the fatigue parameters.

Behavior of 3D-printed polymers under monotonic torsion – A database of 15 different materials

A comprehensive study was carried out to assess the performance of various 3D-printed polymers under monotonic torsion. To the best knowledge of the authors, studies on the torsional behavior of 3D-printed polymers are limited. Fifteen different materials were 3D-printed using the fused deposition modeling (FDM) approach in a flat orientation. For each series, two raster angles i.e., ± 45° and 0°/90° degrees were considered. Circular specimens with a diameter of 10 mm were subjected to a torsional moment with a rate of 0.2 mm/min. Results showed superior performance of specimens with a raster angle of ± 45° in comparison to their 0°/ 90° counterparts. Besides, shear moduli and linear energy absorption per unit volume of the specimens were compared and discussed. Specimen PAHT-CF (polyamide high temperature; CF: carbon fiber) (average shear stress: 49.3 MPa) had the overall best performance in all the investigated parameters; failure of specimens except for polypropylene (PPJET), and thermoplastic polyurethane (TPU) was brittle and sudden and initiated between layers rather than inside layers (i.e., filament fracture); incorporation of carbon fiber didn’t necessarily contribute to improved torsional capacity or ductility. Finally, idealized multi-linear curves were proposed which can aid in the numerical simulation of various 3D-printed polymers. • The performance of 15 different 3D-printed polymers was studied under monotonic torsion. • Idealized multi-linear shear stress-shear strain curves were proposed for numerical simulations.

Modeling size effects in microwire torsion: A comparison between a Lagrange multiplier-based and a [formula omitted] gradient crystal plasticity model

The size-dependent response of metallic microwires under monotonic and cyclic torsion is modeled taking a reduced-order strain gradient crystal plasticity approach involving a single scalar-valued micromorphic variable. It is compared with the response predicted by the CurlFp model proposed in Kaiser and Menzel (2019a), which is based on the complete dislocation density tensor. It is shown that, in cyclic non-uniform plastic deformation processes, the gradient of the scalar-valued internal variable in the reduced-order model predicts isotropic hardening in contrast to kinematic-type hardening produced by the CurlFp model due to a dislocation-induced back-stress component. The arising size effect in the monotonic torsion tests is described by the normalized torque T/R3 as a function of the ratio of the microwire radius R and the characteristic length scale ℓ. In the size-dependent domain, characterized by an inflection point on the corresponding curve, the scaling law T/R3∼(R/ℓ)n can be identified, and explicit relations are found for the power n. The relative evolution of Statistically Stored Dislocation (SSD) and Geometrically Necessary Dislocation (GND) densities during torsion is described in detail.

Characterization of 3D printed ABS specimens under static and cyclic torsional loadings

In this work, the high cycle fatigue response of fused filament fabrication acrylonitrile butadiene styrene solid cylinder specimens under static and cyclic torsional loadings is studied. A first experimental phase was conducted varying the number of external walls between one, two and three contours and with two different infill patterns – concentric and zigzag. Monotonic torsion tests were performed with this first set of specimens to find the best configuration. The best parameter configuration was chosen for a second experimental phase where specimens were subjected to fully reversed load-controlled loading conditions (R=-1) at room temperature. Seven different stress levels were defined to construct the S-N curve of this 3D printed configuration. The microscopic images of the fractured surfaces were also depicted after monotonic and fatigue tests, aiming to study crack initiation, propagation and to characterize the features of fracture surface.

Twinning in rolled AZ31B magnesium alloy under free-end torsion

The mechanical response and microstructure evolution in a rolled AZ31B magnesium alloy were experimentally characterized using companion thin-walled tubular specimens under free-end monotonic torsion. The tubular specimens were made with their axes along the normal direction of the rolled magnesium plate. The shear stress-shear strain response shows a subtle sigmodal shape that is composed of four distinctive stages of strain hardening. Basal slips and tension twinning are operated throughout the shear deformation. Both tension twinning and compressing twinning are favored. Growth and interaction of tension twins with multiple variants lead to formation of twin-twin boundaries (TTBs). The collective hardening effects by twin boundary (TB) and TTB result in a unique rise of the strain hardening rate in Stage II and III. In addition to primary twins, tension-compression double twins and tension-compression-tension tertiary twins with detectable sizes are observed in the tension-twin favorable grains whereas compression-tension double twins are detected in the tension-twin unfavorable grains; all of which become more observable with the increasing shear strain. During Stage IV deformation where TTB formation exhausts, non-basal prismatic slips become more significant and are responsible for the progressive decrease in strain hardening rate in this stage. Swift effect, which is commonly observed in textured materials, is evidenced under free-end torsion. The origin of Swift effect is confirmed to be dislocation slips at a shear strain less than 5% but is predominantly due to tension twinning at a larger plastic strain.

Torsional behavior of additively manufactured nickel alloy 718 under monotonic loading and low cycle fatigue

The high weldability and corrosion resistance of nickel alloy 718 (IN718) make it an ideal material for laser powder-bed fusion (LPBF). However, many of its material properties are still not characterized. Monotonic torsion and low cycle torsional fatigue tests were performed on LPBF IN718 in order to determine its shear properties. Three different print orientations (horizontal, diagonal, vertical) and three separate heat treatments (none, AMS-5662, modified) were tested to determine their effects on the LPBF IN718's torsional behavior. The modified heat treatment was developed to reduce LPBF IN718's anisotropic nature. Monotonic torsion tests revealed that the ultimate shear strength (USS) and yield shear strength (YSS) were dependent on both print orientation and heat treatment, while the shear modulus (G) was only dependent on the print orientation. The USS and YSS improved by at least 42% and 68%, respectively, when either heat treatment was applied. The vertical specimens had the highest G in all cases. The modified heat treatment reduced the difference between the maximum and minimum USS and G from approximately 29% and 38% to approximately 6% and 9%, respectively. The fatigue life appears to be more influenced by the print orientation than the heat treatment. In every case, the horizontal and vertical specimens had the highest and lowest fatigue lives, respectively. Fracture surface analysis revealed similar features observed in conventionally-manufactured material. These results indicate that both the print orientation and the heat treatment must be considered when designing LPBF IN718 parts that will be subjected to torsional loads.

Locking Screws With a Threaded Degradable Polymer Collar Reduce Construct Stiffness Over Time.

The stiffness of locking plates provide increased stability for early fracture healing but may limit late interfragmentary motion (IFM) necessary for secondary bone healing. An ideal plating construct would provide early rigidity and late flexibility to optimize bone healing. A novel screw plate construct utilizing locking screws with a degradable polymer locking mechanism is a dynamic option. Conventional locked plating constructs (group A) were compared with locking screws with a threaded degradable polymer collar before (group B) and after polymer dissolution (group C). Monotonic axial compression, monotonic torsion, cyclic axial load to failure, and IFM at the near and far cortices were tested on synthetic bone models. One-way analysis of variance and post hoc Tukey-Kramer testing demonstrated similar axial stiffness in group A (873 ± 146 N/mm) and B (694 ± 314 N/mm) but significantly less stiffness in group C (379 ± 59 N/mm; F(2,15) = 9.12, P = 0.003). Groups A and B also had similar IFM, but group C had significantly increased IFM at both the near (F(2, 15) = 48.66, P = 2.76E-07) and far (F(2, 15) = 11.78, P = 0.0008) cortices. In cyclic axial load to failure, group A (1593 ± 233 N) and B (1277 ± 141 N) were again similar, but group C was significantly less (912 ± 256 N; F(2, 15) = 15.00, P = 0.0003). All failures were above the 500-N threshold seen in typical weight-bearing restrictions for fracture care. Torsional stiffness demonstrated significant differences between all groups (F(2, 15) = 106.64, P = 1.4E-09). Use of locking plates with a degradable polymer collar show potential for in vitro construct dynamization. Future in vivo studies are warranted to assess performance under combined loading and the effects of decreasing construct stiffness during the course of bony healing.

Effect of strain reversal on the stress-induced martensitic transformation and tensile properties of a metastable β titanium alloy

In this study, the effect of strain reversal on the evolution of microstructure and mechanical properties was investigated. Metastable β titanium alloy samples with single β phase were twisted up to 360° with different strain paths: monotonic torsion (MT) and cyclic forward-reverse torsion (CFRT). The results revealed CFRT with strain reversal accumulated lower dislocation density and less martensitic transformation in comparison with MT under the same accumulative strain. The stress-induced martensitic transformation (SIMT) was retarded by strain reversal and this suppression of martensitic transformation is more pronounced with the decreasing amplitude of strain reversal. It was further observed that CFRT samples with a gradient α″ martensite have a higher mechanical property both in strength and ductility than MT samples, which are due to interactions between α″ martensite and dislocation slip, especially the kinks of α″ martensite.

The Effect of Reverse Strain on Microstructure and Strengthening of Copper Fabricated by Severe Plastic Deformation of Torsion Process

The unidirectional single torsion process of commercially pure copper was followed by different number of reverse turns of torsion deformation. The effect of reverse strain on the material refinement and hardening was investigated. It is found that the grain refinement is significantly blocked in the reverse torsion strain in comparison with that only suffered in monotonic torsion strain. The strengthening slightly decreases with the torsional direction change. This phenomenon is interpreted in terms of the average dislocation density. A qualitative assumption is proposed to explain the retarded phenomenon of material refinement and hardening in the reverse torsion process. The reverse strain maybe improves the uniformity and stress-strain equilibrium of severe plastic deformation induced material.DOI: http://dx.doi.org/10.5755/j01.ms.24.3.18414

Effect of strain reversal on microstructure and mechanical properties of Ti-6Al-4V alloy under cyclic torsion deformation

Abstract Generally, torsion deformation has been recognized as a method of severe plastic deformation (SPD) to obtain a higher shear strain. The effect of strain reversal on the microstructure and mechanical properties was investigated using commercially Ti-6Al-4V alloy by twisting the rods with different effective strain amplitude, such as 180#x00B0;, 270#x00B0;, 360#x00B0; and 450#x00B0; per half cycle. In this work, the microstructure evolution and fracture morphology were carried out by a scanning electron microscope (SEM) and transmission electron microscope (TEM). An Instron 3382 was used for determining ultimate compression strength (UCS). The results show that UCS is very sensitive to cyclic forward-reverse torsion (CFRT) processing and increase distinctly after pre-CFRT. And the value of UCS reaches maximum at 180#x00B0; per half cycle. Besides, monotonic torsion (MT) by twisting the rods in one direction until the fracture occurs was also compared with CFRT. It is found that the ability of work hardening and accumulation of plastic strain is higher for CFRT as compared to MT, which is due to the latticed dislocation in the interior of the grains under CFRT deformation. Grain refinement and fracture feature were discussed to reveal the deformation mechanism of CFRT and MT. The discussion of microstructure evolution and strengthening mechanisms will provide a view to extrapolation to larger strains, finer structures and larger stresses.

Vickers microhardness and microstructure relationship of Ti-6Al-4V alloy under cyclic forward-reverse torsion and monotonic torsion loading

The effect of strain reversal on the hardening and grain refinement of Ti-6Al-4V alloy due to cyclic forward-reverse torsion (CFRT) has been investigated in this study by twisting the bars with different strain reversal amplitude. The results showed that microhardness and its distribution were very sensitive to CFRT and increased distinctly after pre-CFRT pure shear deformation. It was observed that the ultimate microhardness and homogeneity were superior for CFRT as compared to monotonic torsion (MT), while the hardenability exponent of MT is higher than CFRT. Besides microhardness in the center layer and surface layer of a bar exhibited different evolutionary process with the increasing amplitude of strain reversal. Grain refinement induced by latticed dislocation tangle and work hardening enhanced by strain gradient were also discussed to reveal the evolution of microstructure and microhardness.

Experimental Study on Seismic Behavior of Recycled Aggregate Concrete Torsion Beams with ABAQUS

The torsional capacity oftwo recycled aggregate concrete (RAC) beams with 100% recycled coarse aggregate(RCA) and two normal concrete beams subjected to monotonic torsion was investigatedby the finite element software ABAQUS, and the simulated results were comparedwith the experimental results. The investigation shows that recycled aggregateconcrete torsional members have good seismic behavior. The simulated resultsagree well with experimental ones. It can be reference for actual engineering.

Time-Dependent Mechanochemical Response of SP-Cross-Linked PMMA

Time-dependent mechanochemical activation of spiropyran (SP) mechanophores in cross-linked PMMA under creep loading is examined. In contrast to monotonic torsion (constant strain rate) results, the desired force-induced electrocyclic ring-opening of SP to the fluorescent merocyanine (MC) form is achieved at creep stress levels less than the yield stress of the bulk polymer. Lower values of stress require longer time, but much smaller strains for initiation of activation. Additionally, the first measurable detection of the reaction corresponds closely to the maximum creep strain rate, revealing mechanophore activation occurs near the onset of strain hardening, when polymer mobility is highest. The strong correlation between mechanical activation of the spiropyran and the rate of deformation suggests the potential for SP mechanophores as molecular probes of polymer relaxation and flow.

New interpretation of cyclic Swift effects

Abstract The generally accepted view is that induced plastic anisotropy is the main reason for accumulation of axial strains during monotonic and cyclic free-end torsion. In this paper, analytical results and numerical simulations using an elastic/plastic model with yielding described by the isotropic form of Cazacu et al. (2006) criterion and isotropic hardening point to another important cause of this phenomenon. It is shown that such phenomenon can occur in an isotropic material, a slight difference between the uniaxial yield stresses in tension and compression of the material leading to a build-up of inelastic axial strains during cyclic torsion at constant strain amplitude. It is demonstrated that the ratio between the uniaxial yield stresses in tension and compression dictates whether permanent shortening or lengthening of the specimen occurs. Furthermore, it is predicted that by axially preloading the material below its plastic threshold and then subject it to strain controlled cyclic torsion under constant axial load, the axial effects may be either reinforced or reduced. Thus, for any given isotropic material it is possible to estimate the value of the constant load and the strain amplitude that need to be prescribed in order to eliminate these effects.

An Influence of Step Cyclic Loading due to Torsion on Tensile Curve Variation

The paper presents experimental results of tests carried out at room temperature on power engineering steel: 10H2M (11CrMo9-10) using thin-walled tubular specimens under biaxial stress state. The loading programme comprised different types of deformation, i.e. monotonic tension and cyclic torsion in the form of symmetric or asymmetric step-increasing strain amplitude. The main task of the paper was focused on investigation of an influence of the cyclic loading parameters on tensile curve variations. The magnitudes of axial strain and cyclic shear strain amplitude were small and did not exceed 1%. An analysis of the results showed a significant reduction of the axial stress (even equal 90% for the torsional amplitude ±0.8%, in both cases of cyclic loading). An influence of torsion frequency on the tensile stress curve was discovered within the range from 0.005Hz to 0.5Hz.

Material Strain Analysis of CFRP Reinforced RC Columns Subjected to Combined Action of Force by Finite Element Method

Using the finite element software ANSYS to analyze the CFRP strengthened concrete columns.The concrete columns are in the axial force existence situation, many columns should be reinforced by longitudinal and circumferential CFRP because of insufficient capacity. Subject to loading,11 root columns were designed, aiming to the layer number of CFRP, the location and orientation of CFRP, the eccentric distant of specimens.One of them is a non-reinforcement column.Under compression, bending, shearing and monotonic torsion, the nonlinear finite element model was established to test stressed steel bar in column test specimens, including longitudinal tensile reinforcement, longitudinal compression reinforcement and stirrup, as well as CFRP has been analyzed, including stress changing of longitudinal CFRP and transverse CFRP. The torque-strain curves for relationship were discussed among longitudinal reinforcement, stirrup and CFRP.

Modelling Material Behavior of Austenitic Stainless Steel under Monotonic and Cyclic Loadings

Mechanical behavior of the austenitic stainless steel under monotonic and cyclic loading at room temperature has been mathematically predicted. Materials like SS 316 LN exhibit cyclic hardening behavior under cyclic loading. Based on the characteristics of yield surface, cyclic hardening can be classified into isotropic and kinematic hardening. Armstrong-Frederic model is used for predicting the kinematic hardening of this material. It is basically a five parameter, nonlinear kinematic hardening model. Cyclic tests for various ranges were carried out to derive the isotropic material parameter required for modeling. Kinematic hardening material parameter required for modeling were computed based on both monotonic tension and torsion tests. By using these parameters the developed program is able to model the mechanical behavior of austenitic stainless steel under monotonic and cyclic loading conditions at room temperature. Comparison of the predicted results with the experimental results shows that the kinematic hardening material parameters derived from the monotonic torsion tests were in good agreement than that of the monotonic tension tests. Also it is recommended to use more material parameter constitutive models to improve the accuracy of the mathematical predictions for the material behavior under cyclic loading.

High-Temperature Severe Plastic Deformation of Ferritic Steel by Torsion

An ultra-low carbon IF steel was heavily deformed up to an equivalent strain of 36 at various high temperatures of ferrite single-phase region and various strain rates. Effects of temperature and strain rate on the microstructures evolved in torsion deformation were clarified. On the other hand, it was found that homogeneous ultrafine grained structures were not obtained by the present torsion deformation though very high strain was applied. The coarser grain sizes than those obtained by conventional severe plastic deformation (like ARB) were due to the deformation at higher temperature and lower strain rate, but lower fraction of high-angle grain boundaries in the torsion specimen was suggested to be attributed to the characteristics of monotonic torsion (or simple shear) deformation including the way of strain evaluation.

On the Mutual Interactions of Monotonic and Cyclic Loading and their Effect on the Strength of Aluminium Alloys

The paper investigates the interaction of monotonic cyclic loading and their effect on the yield strength of aluminium alloy. Two different loading combinations were considered, i.e. torsion-reverse-torsion superimposed on monotonic tension and monotonic torsion combined with tension-compression cycles. All strain controlled tests were carried out at room temperature using thin-walled tubular specimens. The maximum value of the total cyclic strain amplitude was less than 1%. The influence of amplitude, frequency and shape of cyclic loading signal on the proportional limit and conventional yield point was investigated. The experimental results presented in the paper may be useful to designers of structures that utilize manufacturing processes such as drawing, extrusion, forging of selected semi-finished elements or researchers working on the development of new constitutive equations.