Mechanical Behavior Evolution Research Articles

Mechanical behavior and texture evolution of WE43 magnesium-rare earth alloy in Split-Hopkinson Pressure Bar and Taylor Impact Cylinder Testing

Mechanical behavior and texture evolution of Mg rare-earth alloy WE43 is investigated for strain-rates 10−3/s to upwards of 105/s for the two material conditions - as-cast (AC) and T6 age hardened, rolled plate (RT6). The high strain-rate behavior is tested using both Taylor cylinder impact tests (TC) and split Hopkinson pressure bar tests (SHB) and bulk textures are obtained using neutron diffraction. Unlike the quasi-static strained material, AC and RT6 SHB retained high hardening rates throughout the test, even up to 30% true strain. Moreover, the high strain-rate data revealed that the RT6 material has a much higher strength than the AC material, but similar hardening rates despite significantly different initial texture. The flow stress near yield increased up to 10% for RT6 and up to 30% for AC as the strain-rate increased six orders of magnitude from quasi-static rates 10−3/s to 103/s. Neither material exhibited significant plastic anisotropy over the broad range of strain rates, despite the fact that the RT6 material had a moderately strong initial texture. In the TC tests, the geometric cross-sectional changes and texture along the cylinder from the cylindrical sample foot to head are measured and from the neutron diffraction texture analysis, upper-bound estimates of twin volume fraction are obtained as well as dislocation density from analyzing diffraction peak broadening. Recorded geometrical changes along several loading directions show that the material has deformed homogeneously under impact. Analysis of deformed textures indicates that {101¯2} extension deformation twinning occurred in the RT6 condition over the range of strain rates, with an upper bound estimate of 40% twin volume fraction for approximately 0.10-0.25 true strain. The peak texture components after the impact have their c-axes closely aligned with the impact direction. These observations are presented and rationalized in the paper.

Mechanical behavior and microstructure evolution of Al-Cu-Mg alloy produced by laser powder bed fusion: Effect of heat treatment

Laser powder bed fusion (LPBF) produces significantly different microstructures compared with those produced by conventional manufacturing. The heat treatments of conventional manufacturing may not be suitable for the parts produced by LPBF. This study systematically investigated the effect of heat treatment on mechanical behavior and microstructure evolution of Al-Cu-Mg alloy fabricated by LPBF. The specimen with the optimal solid solution treatment had dislocation strengthening and solid solution strengthening effects, and thus had higher yield strength (YS), ultimate tensile strength (UTS), and elongation than the as-fabricated specimen. High-density acicular ultrafine Al2CuMg phase and some coarse granular Al6Mn phase were observed in the matrix after the post artificial aging. The Al2CuMg precipitation further improved the YS, but the Al6Mn precipitation decreased the UTS and plasticity. As such, by selecting the appropriate heat treatment conditions, the microstructure and mechanical properties of the LPBF Al-Cu-Mg specimens can be comprehensively tailored according to specific user requirements in the application.

Study on high temperature mechanical behavior and microstructure evolution of Ni3Al-based superalloy JG4246A

Ni3Al-based polycrystalline intermetallic compound is a kind of engineering superalloy, which have been used in the adjustment flaps of aeroengine tail nozzle. In order to explore its mechanical properties and microstructure evolution in service, the high temperature flow characteristics and microstructural changes of alloys were investigated by uniaxial isothermal compression tests on Gleeble-1500. The true stress-true strain curves were obtained and the microstructures were analyzed by OM, SEM, and EBSD. Based on the experimental data, three different constitutive models, belonging to phenomenological model, physical-based model, and radial basis function (RBF) neural network model, separately, were established to predict the deformation stress. The results show that the true stress is very sensitive to temperature and stain rate. Flow instability occurred during the deformation process, which caused some decline in the stress. Microstructure evolution under different deformation conditions indicated that the γ' to γn' phase transformation was also related to the degree of deformation and the four stage evolutionary process was identified. The SEM and EBSD results showed that the DRX appeared at the later stage of the deformation. The prediction capabilities of the three models were assessed by correlation coefficient (R), the absolute value of relative error (ARE), and the absolute average error (AARE). The result demonstrated that the RBF neural network had the best ability to predict the flow stress and the coefficient.

Mechanical behaviour and microstructural evolution of Ti-37 at.%Nb alloy subjected to hot compression deformation

As a typical commercial superconducting alloy, Ti-37 at.%Nb alloy is put into engineering application after it experiences plastic deformation at high temperatures. In order to interpret flow behaviour of Ti-37 at.%Nb alloy at elevated temperatures, the constitutive equation of the alloy is constructed based on compressive test at the temperatures (700–1000 °C) and the strain rates (0.0005–0.5s −1 ), where strain compensation is taken into consideration. According to the corresponding constitutive equation, flow stress of Ti-37 at.%Nb alloy is accurately predicted, which is further validated by the experimental data. Simultaneously, the involved microstructural evolution of Ti-37 at.%Nb alloy is characterized in order to further reveal thermal-mechanical behaviour and plastic deformation mechanism of the alloy. Discontinuous dynamic recystallization (DDRX) and continuous dynamic recystallization (CDRX) are found at the same time during hot plastic deformation of Ti-37at.%Nb alloy. Plastic deformation and dynamic recrystallization have a comprehensive influence on textures of Ti-37 at.%Nb alloy. {100}<001>, {100}<011>, {111}<011> and {111}<112> textures are observed in all the deformed Ti-37 at.%Nb samples, where Ti-37 at.%Nb specimens deformed at 700, 900 and 1000 °C exhibit the strongest {100} texture, whereas Ti-37 at.%Nb specimen deformed at 800 °C shows the strongest {111} texture. • Ti-37 at.%Nb alloy is subjected to plastic deformation at high temperatures. • Strain-compensation constitutive equation of Ti-37 at.%Nb alloy is established. • DDRX and CDRX occur simultaneously at the deformed Ti-37at.%Nb alloy. • ►{100}<001>,{100}<011>,{111}<011>and{111}<112> textures are observed.

Mechanical Behavior and Microstructure Evolution during Cold Deformation and Solution Treatment of IN718 Alloy

Mechanical Behavior and Microstructure Evolution during Cold Deformation and Solution Treatment of IN718 Alloy

Mechanical behavior and microstructure evolution for extruded AZ31 sheet under side direction strain

AZ31 magnesium alloy sheets were prepared by a conventional extrusion (CE) and a novel integrated extrusion with side direction strain (SE). The microstructure characterizations, crystallographic texture and mechanical property tests were carried out and compared between the extruded Mg alloy sheets processed by CE and SE. The results indicated that the SE sheets exhibited an excellent combination of strength and ductility. To reveal the side strain effect, the finite element model was employed to investigate the effective stress and strain behavior of the AZ31 magnesium alloy sheets during CE and SE processes. It was found that the SE process was effective in weakening the stress and strain concentration. This implied that it developed an additional side direction strain through the sheet thickness during the hot extrusion. Meanwhile, the side strain shear paths could promote the local accumulation of dynamically recrystallized grains and increase the random high-angle boundaries to achieve weak (0002) basal texture. Important factors including the side strain path and extrusion parameters need to be taken into account to understand the deformation mechanism and microstructure evolution.

An adaptable flexural test fixture for miniaturised polymer specimens

An adaptable flexural test fixture is proposed to characterise the mechanical properties of miniature beam specimens (≤10 mg) at ambient conditions or in the presence of fluids at elevated temperatures. The fixture is validated using representative amorphous and semi-crystalline polymers. The response of miniature specimens is compared against that of medium-sized specimens (≤1 g) on the same fixture and on conventional test equipment. Good agreement is found between the specimen sizes for all materials, but the comparisons highlight small differences attributed to factors such as specimen dimensional accuracy, crystallinity and span-to-thickness ratios. Flexural tests in water at 37 °C using both specimen sizes were performed to investigate the evolution of mechanical behaviour of hydrolytically degraded polylactides. Here, specimen size influences the diffusion timescale of acidic by-products which can reduce or enhance autocatalysis.

Insights into micro-mechanical response and texture of the additively manufactured eutectic high entropy alloy AlCoCrFeNi2.1

In the present study, the evolution of microstructure, texture and high-temperature mechanical behavior of the additively manufactured (AM) eutectic high entropy alloys (EHEA) AlCoCrFeNi2.1 have been investigated. The material was manufactured through laser engineered net shaping (LENS) process. The microstructural investigation revealed constituent phases consisting of dendritic and eutectic features, with the phases having ordered FCC (L12) and BCC crystal structures. The phase fraction of L12 was more across the build (X) face and that of the BCC was more along build plane (Z face). In both the phases, nickel constituted the base element with L12 phase being deficient in Al and the BCC deficient in Cr and rich in Al. The stability of L12 phase was attributed to Co, Cr, and Fe with near equiatomic distribution. Kurdjumov-Sachs (KS)orientation relationship was followed between the ordered L12 and BCC phases along and across the build-up direction. Strain partitioning was observed more in the BCC phase than in the L12 phase during uniaxial compression at all temperatures. Difference in hardness was observed along Z and X directions which further resulted in yield anisotropy during compression test at room temperature. High-temperature compression tests at temperatures 400 °C, 600 °C, 700 °C, and 800 °C revealed that the yield strength increased from room temperature till 400 °C and then started decreasing till 800 °C.

Effect of heterostructure and hetero-deformation induced hardening on the strength and ductility of brass

Heterostructured materials have been reported to possess superior combinations of strength and ductility, which is attributed to hetero-deformation induced (HDI) strengthening and work hardening. However, the influence of heterostructural parameters on the evolution of HDI stress and mechanical behavior during tensile deformation is not well understood. In this paper, heterostructured brass (Cu–30%Zn) was fabricated by cold rolling and partial annealing, to produce heterostructures with different heterostructural parameters, including domain volume fraction, domain thickness/spacing and domain misorientation. It was found that HDI hardening was dominant when the tensile strain was less than ∼4.5%, while conventional dislocation hardening became more effective at higher strain levels. Quick accumulation of geometrically necessary dislocations was found in the domain boundary regions, leading to high HDI stress. Higher domain misorientation was found more effective in developing HDI hardening. These findings elucidate the effect of heterostructure on strength and ductility, which can help with the design of heterostructured materials for superior mechanical properties.

In-situ micro-compression of single-crystal aluminum alloy 6063

The mechanical behavior and microstructure evolution of a single-crystal aluminum alloy 6063 were studied and visualized by in-situ micro-compression experiments. The crystallographic orientation significantly impacts the deformation behavior, and the fluctuation on the stress-strain curve corresponds well to the variation of deformed microstructure. The deformation mechanism was analyzed based on the Schmid factor as well.

Evolution of microstructure and mechanical properties of Ti-based metal-matrix composites during hot deformation

Two Ti-based composites, viz. Ti/TiB and Ti-15Mo/TiB were produced by spark plasma sintering using a Ti-10wt.%TiB2 powder mixture at 1000°C or Ti-14.25(wt.)%Mo-5(wt.)%TiB2 powder mixture at 1400°C, respectively. Specimens of the metal-matrix composites (MMCs) were subjected to uniaxial compression in the temperature range from 500 to 1050°С to determine processing window. Processing maps for both MMCs were constructed and analyzed. Mechanical behavior and microstructure evolution of both MMCs during multiaxial forging (MAF) at 700°C and at a strain rate 10-3 s-1 were studied. The flow stress for the Ti-15Mo/TiB MMC during MAF was ∼2 times higher than that for the Ti/TiB composite. Microstructure evolution during MAF of Ti/TiB MMC was associated with continuous dynamic recrystallization of the titanium matrix and shortening of TiB whiskers by a factor of ~3. The Ti-15Mo/TiB composite microstructure after did not demonstrate the development of recrystallization.

Mechanical Behavior and Energy Evolution of Sandstone considering Slenderness Ratio Effect

To study the influence of slenderness ratio effect on the mechanical behavior, acoustic emission properties, and energy evolution of sandstone, the uniaxial compression tests coupled with acoustic emission technology are carried out at different slenderness ratios D (0.5, 1.0, 1.5, 2.0, 3.0). The results show that a logarithmic function relationship is observed between the peak strength, the peak strain, and the elastic modulus with slenderness ratio. The failure patterns of the tested sandstone varied significantly with the increasing slenderness ratio. When the slenderness ratio, D, is lower than 1.5, complex failures and multiple shear planes are formed, while simple failures and single shear planes are generated at D larger than 1.5. Besides, the AE ringing counts are more obvious with a higher slenderness ratio, D, at the initial compression stage due to the greater body volume and more defects in the sandstone. The energy evolution curves and energy ratio distribution curves can be divided into four stages, corresponding to the stress‐strain curves.

Mechanical behavior and microstructure evolution of TC4 alloy during high temperature plastic deformation

In this paper, the mechanical behaviour and microstructure evolution of TC4 titanium alloy during high temperature plastic deformation are studied. The compression experiment was carried out on the Gleeble-3800 thermal simulator at the deformation temperature ranging from 900℃~1100℃ and at the strain rate of 0.1/s~10/s. The experimental results show that the flow softening mechanism of TC4 titanium alloy is dynamic recrystallization under condition of high temperature deformation. As the deformation temperature increases, the volume fraction and size of the β-transformed tissue become larger, and more acicular martensite appears in the β-transformed tissue. With the increase of strain rate, the grain size is reduced. Moreover, under the condition of high-temperature deformation, TC4 titanium alloy has obvious discontinuous yield phenomenon, and the higher the deformation temperature is, the more obvious the discontinuous yield phenomenon is. At low strain rate, TC4 titanium alloy has a slight strain hardening in a small strain rage, then it exhibits the characteristic of continuous softening flow, and it eventually tends to steady state. At high strain rates, TC4 titanium alloy exhibits wave yielding phenomenon.

Mechanical behaviour and microstructural evolution in fine grain Ti-6Al-4V alloy under superplastic conditions

Ti-6Al-4V is able to support high level of deformations like superplastic deformation for aeronautical structural applications. However, the applied temperature during forming induces changes in phase fraction, which may have an impact on the mechanisms of deformation involved and the final part. Mechanisms described in the literature, like dislocation glide, diffusional creep, Grain Boundary Sliding (GBS) accommodated by dislocation or diffusion, are still controversial as there are mainly based on post mortem analysis or on stress-strain data. The purpose of this work was to combine interrupted tensile tests and heat treatments to improve the understanding of the mechanisms of deformation on each stage of deformation. The chosen test temperatures were 750°C and 920°C which correspond to different β phase fractions. The microstructural features like grain size and phase fraction were studied by Scanning Electron Microscope (SEM) combined with image analysis. Moreover, EBSD was used to follow the change of crystalline orientation of α grains to distinguish the involved mechanisms as a function of the deformation. Indeed, it would appears that several mechanisms could be activated depending on the deformation stage and on the temperature.

Mechanical behavior, deformation mechanism and microstructure evolutions of ultrafine-grained Al during recovery via annealing

Ultrafine grained (UFG) metals and alloys typically exhibit mechanical and thermal instabilities, partially due to the high density of lattice defects, which limits their engineering applications. Annealing represents a simple and effective way to regain strain hardening, ductility and thermal stability, and stabilize the UFG structures. In this study, we systematically investigated the mechanical behavior, microstructural evolution, fracture and deformation mechanisms of UFG Al during recovery via low-temperature annealing. More specifically we report that low-temperature annealing at 250 °C for 20 min increased the ultimate tensile strength by 10% from 190 to 208 MPa and tensile ductility by 50% from 4.5 to 6.8% without any changes in yield strength (180 MPa). Microstructural analyses indicate that the annealing increased the average grain size from 740 to 840 nm, dislocation density decreased from 5 × 1014 m-2 to 1 × 1014 m-2, while the nature of the grain boundaries and associated precipitated phases remained unchanged. Moreover, annealing led to modification of statistically stored dislocations into low-energy dislocation walls (sub-grain boundaries). Results from the fracture surface morphology indicated that the enhanced ductility of the annealed sample was related to the activation of numerous homogeneous micro shear bands, which were controlled by cooperative grain boundary sliding. These observations suggest that the dislocation walls formed during recovery promoted the formation of micro shear bands/cooperative grain boundary sliding and thereby enhanced the ductility.

Damage to carbon fibre reinforced polymers (CFRP) in hole-clinched joints with aluminium alloy and CFRP

This study aimed to investigate the damage to carbon fibre reinforced polymers (CFRP) in hole-clinched joints composed of CFRP and aluminium alloy 5754. A continuous damage model (CDM) based on the modified Hashin failure criterion was proposed to predict the mechanical behaviour and damage evolution of the CFRP, and the CDM was validated using open hole tensile tests. The effect of the CFRP hole radius on the joint quality was investigated to obtain the optimal joining conditions. Furthermore, a numerical model for the hole-clinching process was developed to understand the forming mechanism of the joint and the damage patterns in the CFRP. The CFRP damage patterns with different ply angles in the hole clinching process were evaluated using numerical simulations. The proposed CDM can predict the mechanical behaviour and complex damage modes of CFRP. An increased hole radius generally corresponds to an increased neck thickness and a decreased undercut of the joints. Hole clinching cannot effectively join CFRP with a 0° ply, and delamination is most severe in joints with a complex angle ply.

Effect of nano-sized particles on grain structure and mechanical behavior of friction stir welded Al-nanocomposites

Weldability of heat-treatable 6061-T6 aluminum alloy results in deterioration of mechanical properties due to dissolution of strengthening precipitates in the nugget zone of friction stir welded joints. These properties were improved by addition of reinforcement particles in the weld joint line. In the present work, attempts were made to produce 6061-T6 Al-based nanocomposites using the friction stir welding process by incorporating titanium oxide nanoparticles into the aluminum matrix for microstructure refining of the nugget zone and prevent the grain growth in the heat-affected zone. The effect of addition of nanoparticles on the evolution of grains structure and mechanical behavior of friction stir welded samples based on different combinations of rotational and travel speed was studied and discussed. Results revealed that the unreinforced samples were successfully welded at both low and high heat inputs, whereas the reinforced samples are not feasible at tool rotational speed (ω) &lt; 2000 r/min and transverse speed (v) &gt; 70 mm/min, respectively. The significant refining of grains in the nugget zone is possible with addition of nanoparticles via the Zener-pinning effect. A more pronounced increment in tensile strength, microhardness, and wear properties was observed compared to sample without nanoparticles under the same processing parameters due to embedment of nano-sized particles in the weld nugget zone.

Effect of Electropulsing on Surface Mechanical Behavior and Microstructural Evolution of Inconel 718 during Ultrasonic Surface Rolling Process

In the current study, the surface mechanical behavior and microstructural evolution of Inconel 718 superalloy processed by the ultrasonic surface rolling process (USRP) and electropulsing-assisted ultrasonic surface rolling process (EP-USRP) were carefully analyzed. The experimental results suggested that after EP-USRP with a frequency of 400 Hz, significant enhancements in Vickers microhardness and nanoindentation hardness were achieved compared to those of USRP specimens, with increases of 13.6 and 9.9%, respectively. Moreover, the machined surface quality, wear resistance, and thermal stability were also improved after EP-USRP (400 Hz). These enhancements in mechanical behavior are closely related to the microstructural evolution induced by electropulsing. Under the coupling of thermal and athermal effects of high-energy electropulsing, the deformation limit of USRP is surpassed and a new balance is achieved between the electropulsing softening effect and the ultrasonic rolling hardening effect. Therefore, further grain refinement, improved plastic deformation ability in the strengthened layer, and the interaction effect between nano-sized precipitates and grain boundaries are probably the main reasons for these results.

Mechanical Behavior and Microstructure Evolution of a Ti-15Mo/TiB Titanium–Matrix Composite during Hot Deformation

A Ti-15Mo/TiB titanium–matrix composite (TMC) was produced by spark plasma sintering at 1400 °C under a load of 40 MPa for 15 min using a Ti-14.25(wt.)%Mo-5(wt.)%TiB2 powder mixture. Microstructure evolution and mechanical behavior of the composite were studied during uniaxial compression at room temperature and in a temperature range of 500–1000 °C. At room temperature, the composite showed a combination of high strength (the yield strength was ~1500 MPa) and good ductility (~22%). The microstructure evolution of the Ti-15Mo matrix was associated with the development of dynamic recovery at 500–700 °C and dynamic recrystallization at higher temperatures (≥800 °C). The apparent activation energy of the plastic deformation was calculated and a processing map for the TMC was constructed using the obtained results.

Experimental Study on Mechanical Properties, Failure Behavior and Energy Evolution of Different Coal-Rock Combined Specimens

To investigate the effect of the pure coal/rock strength on the mechanical behavior, failure behavior, and energy evolution of coal-rock combined (CRC) specimens, an AG-X250 Shimadzu Precision Universal Test was used to conduct uniaxial compressive loading, uniaxial cyclic loading, and unloading compression experiments on pure coal, pure rock, and different CRC specimens. The results show that the uniaxial compressive strength, Young’s modulus, and peak strain of the CRC specimen mainly depend on the coal specimen instead of the rock strength. The major failure modes of CRC were the shearing fracture and axial splitting failure, and for the CRC specimen with the same hard rock, the CRC specimen severely failed due to axial splitting cracks. In addition, the released elastic energy Ue, dissipated energy Ud, and kinetic energy Ur increase with increasing rock mass/coal strength, and for CRC specimen with the same coal, the greater the difference in strength between the rock and coal is, the greater the kinetic energy is.