Mechanical Deformation Behavior Research Articles

Effect of Recycling PBT Powder on Mechanical Strength and Deformation Behavior of Laser Sintered Parts

Effect of Recycling PBT Powder on Mechanical Strength and Deformation Behavior of Laser Sintered Parts

Effect of heat treatment time on the microstructure and mechanical deformation behavior of additive-manufactured AlSi10Mg components

The AlSi10Mg alloy was developed using a selective laser melting (SLM) process, followed by stress relieving at $$300^\circ \hbox {C}$$ for 2 and 4 h respectively. The effect of the heat treatment time on the microstructural and mechanical properties was determined. AlSi10Mg powder with an average particle size of $$47\,\upmu \hbox {m}$$ was successfully melted with laser energy density of $$53.7\,\hbox {J/mm}^{3}$$ . The samples were examined using both a scanning electron microscope and an optical microscope, to determine their microstructural properties. The samples were subjected to a tensile test and nano-indentation in order to determine the effect of heat treatment time on the microstructures and mechanical properties. The 2-h stress relieved alloy revealed fine silicon precipitates within the semi-elliptical track. The 4-h stress relieved alloy formed coarser silicon precipitates without semi-elliptical tracks. The results showed: improvement in deformation behaviour, with an increase in stress-relieving time; while the strength was compromised. The 2-h stress relieved sample showed higher strength, due to the fine silicon precipitates, when compared to the 4-h stress relieved sample, which showed excellent ductility. The lower strength was attributed to coarser silicon particles within the microstructure.

High temperature tensile properties, deformation, and fracture behavior of a hybrid-reinforced titanium alloy composite

In present work, a hybrid-reinforced titanium alloy has been β forged and heat treated successively. The microstructure evolution, deformation mechanism and fracture behavior were investigated to evaluate the contribution of HT on strength. The fine zone was formed after HT at the prior β grain boundary, and the (TiB + TiC + Y2O3) reinforcement could significantly enlarged the area of fine zone and homogenized the microstructure. Silicide precipitation was also observed in intra lamellar and α/β boundary after HT, thereby increasing the strength via Orowan strengthening mechanism. In addition, the deformation mechanism analysis indicated that the grain boundary slip contributed a great effort to the high temperature deformation during tensile testing. Due to the formation of fine zone and silicide precipitation, the grain boundary strength and intragranular strengths both improved. However, the equal-strength temperature improved more thus leaded to a high yield strength in (TiB + TiC + Y2O3)/α-Ti composite after HT. This result also had a substantial influence on fracture morphology, which achieved considerable strength in the matrix and composite at elevated temperature.

Superior Temperature-Dependent Mechanical Properties and Deformation Behavior of Equiatomic CoCrFeMnNi High-Entropy Alloy Additively Manufactured by Selective Laser Melting

The microstructure, temperature-dependent mechanical properties and deformation behaviors of equiatomic CoCrFeMnNi high-entropy alloy (HEA) additively manufactured by selective laser melting (SLM) were investigated. SLM-built HEA had a face-centered cubic (FCC) single-phase random solid solution. In addition, SLM-built HEA was composed of epitaxial growth grains, dislocation network and nano-sized oxides. Room- and high-temperature compression tests confirmed that SLM-built HEA has outstanding mechanical properties in all temperature ranges compared to equiatomic CoCrFeMnNi HEAs reported up to the present. The excellent mechanical properties of SLM-built HEA were achieved with fine grains, high dislocation density and fine precipitates at low temperatures (25 °C to 600 °C), and by high dislocation density and fine precipitates at high temperatures (700 °C or higher). On the other hand, the deformation microstructure showed that slip and deformation twins are the main deformation mechanisms from 25 °C to 600 °C, and slip and partial recrystallization are the main deformation mechanisms above 700 °C. Based on the above findings, this study also discusses correlations among the microstructure, superior mechanical properties and deformation mechanisms of SLM-built equiatomic CoCrFeMnNi HEA.

Deformation mechanisms of the subgranular cellular structures in selective laser melted 316L stainless steel

Selective Laser Melting (SLM) of certain alloys such as Stainless Steel yields a unique microstructure consisting of complex subgranular cell structures produced by ultra-fast cooling during solidification. Owing to the presence of these cell structures, SLM-fabricated 316L Stainless Steel displays a superior yield strength and hardness. Despite the significance of the distinctive cellular structures, their deformation characteristics and the mechanisms responsible for superior mechanical properties are not well-understood yet. In this paper, the mechanical deformation behavior of the complex cellular structures observed in the SLM-fabricated 316L Stainless Steel is investigated by performing a series of molecular dynamics simulations of uniaxial tension tests. The atomic configurations in the computational models of the cell structures are inspired by the SEM images of the microstructure of 316L Stainless Steel. The effects of compositional segregation of alloying elements, distribution of austenite and ferrite phases in the microstructure, subgranular cell sizes, and pre-existing (grown in) nano-twins on the tensile characteristics of the cellular structures are investigated. The highest yield strength is observed when the Ni concentration in the cell boundary drops very low to form a ferritic phase in the cell boundary. However, the flow stress is found to be the highest when both the cell boundary and cell interior are austenitic with higher Ni concentration in the cell interior. Moreover, governed by the initial dislocation density, the subgranular cell size has an inverse relationship with mechanical strength. Finally, the nano-twinned cells exhibit higher strength in comparison with twin-free cells as a result of the dislocation pinning at the twin boundaries. The investigation on the effect of twin spacing reveals a Hall-Petch type phenomenon in which smaller twin spacing strengthens the nano-twinned subgranular cells further.

Tensile Properties of Composite Reinforced with Three-Dimensional Printed Fibers.

This study used melt-electrospinning writing to fabricate three-dimensional fiber constructs by embedding them in a polyvinyl alcohol (PVA) matrix to obtain thin composite films. Fourier transform infrared spectroscopy (FTIR) and dynamic scanning calorimetry (DSC) were used to demonstrate an interaction between the polycaprolactone (PCL) fibrous phase and the PVA matrix phase. Following this, the mechanical deformation behavior of the composite was investigated, and the effect of reinforcement with three-dimensional fibrous constructs was illustrated. The specific strength of the composite was found to be five times higher than the specific strength of the neat PVA matrix. Additionally, the specific toughness of the composite was determined to be roughly four times higher than the specific toughness determined for the neat PVA matrix. These results demonstrate the potential of using melt-electrospinning writing for producing three-dimensional fibrous constructs for composite reinforcement purposes.

Anisotropic mechanical properties and deformation behavior of low-carbon high-strength steel component fabricated by wire and arc additive manufacturing

Wire and arc additive manufacturing (WAAM) is an efficient technique for fabricating large and complex components that are applied in the manufacturing industry. In this study, anisotropic mechanical properties of a low-carbon high-strength steel component fabricated by WAAM were investigated via mechanical testing, and the transversal and longitudinal deformation behavior of the component were studied using the digital image correlation (DIC) method. Additionally, the features of microstructure, texture, and fracture mode of the inter-layer area and deposited area were also investigated to reveal the mechanism of anisotropy. The results showed the mechanical properties of longitudinal specimens were inferior to that of the transversal specimens. Several strain concentration zones in the longitudinal specimen were relevant to the inter-layer characteristics observed from the fracture surface and macrostructure, which was confirmed by the strain evolution recorded by DIC. The inter-layer areas were proved to be the weak link in the deposited component by scanning electron microscope (SEM) and electron backscatter diffraction (EBSD) analysis results, including various phase composition, phase morphology, misorientation angle, grain size, Schmid factor, and texture. Finally, based on the fractography analysis, anisotropy resulted from inter-layer zones is also confirmed via the comparison of transversal and longitudinal fracture morphology.

A progress report on the MAB phases: atomically laminated, ternary transition metal borides

ABSTRACTThe MAB phases are atomically layered, ternary or quaternary transition metal (M) borides (TMBs), with the general formula (MB)2zAx(MB2)y (z = 1–2; x = 1–2; y = 0–2), whose structures are composed of a transition M-B sublattices interleaved by A-atom (A = Al,Zn) mono- or bilayers. Most of the MAB phases were discovered before the 1990s, but recent discoveries of intriguing magnetocaloric properties, mechanical deformation behaviour, catalytic properties, and high-temperature oxidation resistance has led to their ‘re-discovery’. Herein, MAB phase synthesis is reviewed and their magnetic, electronic, thermal, and mechanical properties are summarized. Because the M-B layers in the MAB phases structurally resemble their corresponding binaries of the same M:B stoichiometry, the effects of the A-layers on properties are discussed. Inconsistencies in the literature are critically assessed to gain insights on the processing-structure-property relations, suggest fruitful avenues for future research, and identify limitations for prospective applications.

Mineralogical characterization and strain analysis of the Marcellus shales

Due to the complex structure of the brittle formations like shale, their microcracking and mechanical deformation behavior are not well known. To understand the fundamental factors at the micron scale, Marcellus shales were cored both parallel and perpendicular to the bedding orientation and mechanically tested through triaxial creep test under constant stress. The parallel-bedded shales exhibited higher level of permanent strain in the radial direction, which increased with increasing time. This also confirmed their anisotropic nature due to the bedding. Their advanced characterization via X-ray diffraction (XRD) and Raman spectroscopy techniques before and after the creep tests revealed the mineralogical heterogeneity, and the presence of an organic matter (kerogen) concentrated in the microcrack areas. Besides, the XRD peak shifts and changes in peak shape indicated that there was a certain level of macrostrain and microstrain in the shale. Further investigation of the XRD peak shape (integral breadth) changes using the Williamson-Hall method demonstrated a higher concentration of lattice defects and associated microstrain (inhomogeneous lattice strain) present in the calcite phase compared to the quartz. The parallel-bedded shales also revealed a higher level of microstrain with respect to the perpendicular-bedding. The results proved that the microcracking (initiation and propagation) and associated mechanical deformation of the Marcellus shales were mostly influenced by the presence of organic matter, microstrain level (defect concentration) in the calcite mineral, and the bedding orientation.

Chitosan in-situ grafted magnetite nanoparticles toward mechanically robust and electrically conductive ionic-covalent nanocomposite hydrogels with sensitive strain-responsive resistance

Hydrogels with a combination of high mechanical properties and excellent electrical conductivity are promising for soft and wearable electronics devices. However, the trade-off between poor strength/toughness and high electrical resistance of the hydrogels severely hamper their practical application in diverse areas. In this work, we reported a facile and effective strategy for fabricating mechanically robust and electrically conductive nanocomposite hydrogels via incorporating chitosan in-situ grafted magnetite nanoparticles combined with multiple ionic-covalent interactions. The obtained nanocomposite hydrogel delivers a remarkable mechanical strength up to 2.33 MPa and high toughness of 18.18 MJ m-3 at a relatively high water content (80 wt%). Based on the creep/recovery experimental results and analysis (Burger's model and Weibull distribution function), the effect of multiple ionic-covalent interactions among the double-networks and chitosan in-situ grafted nanoparticles on the viscoelastic behavior of the hydrogel was discussed and clarified. In addition, the resultant nanocomposite hydrogel exhibits sensitive strain-induced resistance change under both compressive and tensile stress as well as outstanding stability and repeatability, which can accurately and repeatedly monitor both large mechanical deformation (e.g. tensile strain up to 600%) and human behaviors (e.g., motions of joints and facial expressions). This study offers a new scenario to design and develop a mechanically robust hydrogel with sensitive strain-responsive resistance, showing potential applications in electric skin, motion detection, wearable electronics, etc.

Orientation-Dependent Deformation Behavior of 316L Steel Manufactured by Laser Metal Deposition and Casting under Local Scratch and Indentation Load.

This study analyzes the local deformation behavior of austenitic stainless steel 316L, manufactured conventionally by casting and additively by laser metal deposition (LMD). We produced directionally solidified 316L specimens with most grains showing (001) orientations parallel to the longitudinal specimen axis. We conducted nanoindentation and scratch experiments for local mechanical characterization and topography measurements (atomic force microscopy and confocal laser scanning microscopy) of indentation imprints and residual scratch grooves for the analysis of the deformation behavior and, in particular, of the pile-up behavior. The local mechanical properties and deformation behavior were correlated to the local microstructure investigated by scanning electron microscopy with energy dispersive X-ray spectroscopy and electron backscatter diffraction analysis. The results show that the local mechanical properties, deformation behavior, and scratch resistance strongly depend on the crystallographic orientation. Nearly (001)-oriented grains parallel to the surface show the lowest hardness, followed by an increasing hardness of nearly (101)- and (111)-oriented grains. Consequently, scratch depth is the greatest for nearly (001)-oriented grains followed by (101) and (111) orientations. This tendency is seen independently of the analyzed manufacturing route, namely Bridgman solidification and laser metal deposition. In general, the laser metal deposition process leads to a higher strength and hardness, which is mainly attributed to a higher dislocation density. Under the investigated loading conditions, the cellular segregation substructure is not found to significantly and directly change the local deformation behavior during indentation and scratch testing.

Design and manufacture of a high precision personalized electron bolus device for radiation therapy

AbstractThis paper investigates a novel design and manufacturing methodology for an unmet need in radiation therapy—dose optimization of electron beam bolus. A thin‐walled bolus design was proposed which when filled with water, optimized the dose distribution for the electron beam radiation therapy. The fabrication of this design was accomplished by the fused deposition modelling (FDM) additive manufacturing (3D Printing) technique. Acrylonitrile butadiene styrene (ABS) and polycarbonate (PC) materials were employed for fabricating the electron boluses. Our data show that both the materials displayed expected radiation modulation. The designed boluses were subjected to higher radiation doses (50 Gy) and revealed permissible deformations based on the dimensional deviation analysis. Mechanical deformation tests were performed to evaluate the bolus design and materials under different loading conditions. The results showed that the ABS material had superior mechanical strength and deformation behaviour as compared to PC. Finite element analysis of the bolus designs revealed regions of stress concentration and potential failure modes which were validated by experimental results. The design of experiments analysis showed that bolus thickness and material type had a profound influence on the mechanical deformation of the bolus. The proposed radiation device technology is cost‐effective, eco‐friendly and amenable to changes in the tumour size and shape, compared to current methods. This paper provides a framework for the design and manufacture of radiation modulation devices that can be implemented for proton, electron and photon cancer therapies.

Nanoindentation study of the mechanical properties and deformation behavior of nanoporous alumina films

Over the past decade, anodic aluminium oxide (AAO) has become one of the most widely used materials as a platform for developing new types of devices in micro- and nanotechnology. Due to the potential use of highly ordered honeycomb porous AAO membranes in many engineering applications, considerable attention is being paid to the mechanical characterization of such thin films. In this study, the mechanical properties and deformation behavior of a nanoporous alumina film were investigated by nanoindentation. AAO films with an average pore diameter of 40 nm were fabricated electrochemically. The morphology and the mechanical properties of AAO were studied using scanning electron microscopy and nanoindentation, respectively. The force-displacement dependences obtained revealed that in the case of a freestanding AAO membrane the sample demonstrates extremely high elasticity. The indentation modulus and the hardness were found to decrease nonlinearly with an increase in the applied force.

Effect of heat treatment conditions on mechanical properties and springback of 6061 Aluminum alloy sheets

The mechanical properties and bending deformation behaviors of homogenization treated (HT), solution treated (ST), natural aging (NA) treated and T6 6061 aluminum alloy sheets were investigated by tensile tests and three-point bending tests, respectively. The results showed that the heat treatment conditions have a significant impact on mechanical properties and bending characteristic. Bending radius and thickness of the HT alloy is the highest, and its springback angle is the lowest. However, the deformation mechanism of T6-8h alloy is just the opposite. The bending characteristics are attributed to the combined effects of yield strength, strain-hardening exponent and coefficient of the neutral layer. The simulation results are in good agreement with the experiment.

Effect of Grain Size on the Shear Banding Behavior of Ti-6Al-4V Alloy Under Quasi-Static Compression

Ti-6Al-4V alloys with average grain sizes of 0.3 to 1.5 μm were fabricated by high-energy ball milling (HEBM) and spark plasma sintering (SPS). Mechanical properties and deformation behaviors of sintered Ti-6Al-4V samples were investigated. The compressive yield strength increases while the ductility diminishes when the average grain size of Ti-6Al-4V decreases. Localization of plastic deformation occurs in all the fine-grained titanium alloys under quasi-static compression. Macro shear bands are observed in the deformed Ti-6Al-4V specimens with average grain size of 1.5 μm. When the grains are refined to ultrafine-grained regime, not only macro shear bands but also micro shear bands are generated in the deformed specimens. It is found that the spacing distance between macro shear bands increases once the micro shear bands are formed, indicating that the generation of profuse micro shear bands could suppress the nucleation of macro shear bands.

Effects of temperature and strain rate on plastic deformation mechanisms of nanocrystalline high-entropy alloys

The nanocrystalline high-entropy alloys (HEAs) can be regarded as ideal substitution materials for use in aero engines due to their outstanding mechanical properties. Owing to the crucial importance on the evaluation of mechanical properties in nanocrystalline HEAs, the identification of the plastic deformation mechanism remains a challenging topic. Considering the fact that nanocrystalline HEAs suffer from the high-temperature service, the roles of strain rate and temperature on their deformation characteristics should be examined. Here, we report the impact of strain rate and temperature on the mechanical properties and deformation behaviors of nanocrystalline HEAs. This issue was investigated by a series of molecular-dynamics tensile tests at different strain rates ranging from 5 × 107 to 1 × 1010 s−1 and temperatures ranging from 10 to 1,200 K. The results show that the dislocation slip controls the preferred deformation mechanism at low temperatures and high strain rates. When the temperature rises and strain rate reduces, grain-boundary sliding dominates the primary deformation mechanism at elevated temperatures. Moreover, the occurrence of the face-centered-cubic (fcc) to body-centered-cubic (bcc) phase transformation can effectively enhance the plasticity of HEAs. The synergistically-integrated experimental and modeling efforts at the nanoscale will help understand, control, and optimize the mechanical behaviors of nanocrystalline HEA systems, thereby enabling the development of advanced nanocrystalline HEAs.

Effect of the distribution state of transition phase on the mechanical properties and failure mechanisms of the W–Mo–Cu alloy by tuning elements content

Forming a transition phase (TP) layer between W and Cu phase can significantly improve the ductility of the W–Mo–Cu alloy. But, how the elements content affects the microstructure and mechanical properties of the W–Mo–Cu alloy is still unknow. In present work, to investigate these effects in detail, the W–Mo–Cu alloys with different TP layer structure were fabricated by the infiltration method by changing W and Mo content. The effects of distribution state of TP on the mechanical properties, deformation behavior and failure mechanisms of W–Mo–Cu alloys in tensile and compressive process at different temperature were investigated. The results suggest that by increasing Mo content, TP layer structure transforms from semi-continuous to completely coated network, leading to the high ductility of W–Mo–Cu alloy. Additionally, as compared to weak interfacial bonding between W and Cu interfaces, formation of TP layer can increase the interfacial strength then to significantly improve ductility and tensile strength. The effect of the TP layer structure induced by Mo content on the deformation behavior and failure mechanism of the W–Mo–Cu alloy are also discussed.

Improving performance of friction stir welded AZ31/AM60 dissimilar joint by adjusting texture distribution and microstructure

Inhomogeneous deformation, which was usually found during the deformation of friction stir welding (FSW) Mg alloys joints, could deteriorate the joint performance. This work aims to understand the effect of microstructure and texture distribution in joint on mechanical properties and deformation behavior of the FSW dissimilar Mg alloys joints. Two kinds of AZ31/AM60 dissimilar Mg alloys joints were obtained via FSW at two sets of welding parameters (higher rotation rate and welding speed (HRW), lower rotation rate and welding speed (LRW)). Electron backscatter diffraction measurements were conducted to examine the microstructure and texture distribution of these two joints. The results showed that the joint with finer grains, weaker texture and higher nugget zone (NZ) interface angle was obtained with HRW. The weaker texture and finer microstructure were beneficial to the homogeneous deformation of the joint. The larger angle between the NZ interface and the transverse direction (about 75°) made it away from the maximum shear force direction (45°) to avoid premature fracture. With these advantages, the mechanical properties of the joint with HRW were better than that with LRW. The yield strength, ultimate strength and elongation were improved 14.4%, 19.7% and 63.7%, respectively. In addition, the grain size of AZ31 of NZ in two joints was smaller than that of AM60. All the joints fractured at the AM60 side near the NZ boundary during the tension tests. This was mainly attributed to the larger grain size and higher Schmid factor of basal slip at the AM60 side near the NZ interface. This study provided some insights in understanding the improvement of the dissimilar FSW Mg joint performance by controlling texture distribution and microstructure.

Differences in mechanical behaviors and characteristics between natural graphite/copper composites and carbon-coated graphite/copper composites

Natural graphite/copper (NG/Cu) composites and carbon-coated graphite/copper (CCG/Cu) composites were prepared via powder metallurgy by using electrolytic copper powder, natural graphite and phenolic resin as raw materials. The mechanical deformation behaviors and characteristics and the structure evolution of the two composites under the actual force form during friction (bending and compression) were investigated in detail. The results show that CCG/Cu composites exhibit ductile fracture and can withstand higher loads in the bending test, which is due to a high compactness and continuity matrix and a uniform distribution of intact CCG, while NG/Cu composites show brittle fracture. Owing to the low compactness and continuity matrix and the incomplete NG structure of NG/Cu composites themselves, the deflection and tear of matrix, the deflection and lamellar layers slide of NG and some NG connection occur from deformation to failure in the compression test, and these structural defects are exacerbated until the main crack penetrates through the sample, leading to failure. Although CCG/Cu composites eventually fail in the compression test, carbon coating with phenolic resin on natural graphite effectively delays the deformation and failure and improves the compression strength of CCG/Cu composites. This work provides a reliable mechanical analysis for the failure mechanism of graphite/copper composites during friction.

Experimental and numerical study of dynamic performance of CVAR subjected to regular wave and platform motion

Compliant vertical access risers (CVAR) offer significant economic benefits and prospects for development because of their special configuration. In this paper, the dynamic performance of CVAR is studied by model experiments and numerical simulations. Based on virtual work and variational principles, a vibration equation considering the large deformation mechanical behaviors of CVAR with the influences of bending stiffness and non-uniform internal flow is proposed. To verify it, model experiments on the CVAR are firstly conducted and compared the results with those of a numerical simulation. Time-domain analyses of key nodes, regular wave analysis and dynamic response at different positions of the buoyancy module were then carried out. The vibration near the platform was the largest due to the wave load, and decreased rapidly when in the transitional region. The minimum tension of the transition zone was even subzero at the far end, which means the CVAR is unstable when the platform subject to regular wave conditions. When the buoyancy block was above 1000 m, tension at the bottom was smaller than 672 kN, which will cause the lower region to become catenary shaped and the CVAR to lose its unique operational advantage.