Mechanical Properties Of Different Regions Research Articles

Microstructure and mechanical properties of medium-thickness TC4 titanium alloy narrow gap welded joint

In this study, narrow-gap hot wire vibrating tungsten inert gas arc welding (TIP-TIG) technology was employed to achieve reliable welding of 20 mm thick TC4 alloy plates. Microstructure and mechanical properties of different regions within the welded joint were particularly investigated. The results show that the heat-affected zone (HAZ) exhibited a typical bimodal microstructure consisting of equiaxial α phase, αʹ phase, and β phase. Meanwhile, the weld center showed a basket-weave pattern of α phase and β phase. Microhardness gradually decreased from the base metal towards the weld center, with an average microhardness of 315 HV0.2 at the weld center. The welded joints exhibited an average tensile strength of 1043 MPa, and all samples underwent ductile fracture.

Comprehensive study on the differences in microstructure and mechanical properties of Mg–Li alloy fabricated by additive manufacturing, casting, and rolling

In order to explore the forming mechanism of direct energy deposition of magnesium-lithium alloy wire with high lithium content, this study introduces a novel approach utilizing Cold Metal Transfer Wire Arc Additive Manufacturing (CMT-WAAM) to successfully fabricate thin-walled structures of LA103Z Mg–Li alloy. A comprehensive comparison was conducted to evaluate the microstructure and mechanical properties of different regions on CMT-WAAM samples, in addition to cast and rolled samples. The microstructure of CMT-WAAM samples is mainly composed of β-Li phase and fine needle shaped α-Mg phase, exhibiting a notable divergence from the microstructure observed in cast and rolled samples. It is noteworthy that the mechanical properties along the deposition direction exhibited significant variability in CMT-WAAM samples, but no significant anisotropy is discerned in the mechanical properties along the deposition and scanning directions. The discrepancies in mechanical properties across different regions are predominantly attributed to variations in grain size, and the size and proportion of the α-Mg phase and secondary phases, which are related to the low heat input and high cooling rate of the CMT-WAAM process. The mean tensile strength of CMT-WAAM samples is 159.5 MPa, marking a respective increase of 30.7% and 13.9% compared to cast and rolled samples. These findings underscore the outstanding strength of CMT-WAAM samples compared to conventionally formed samples. This study provides novel insights into additive manufacturing of dual-phase Mg–Li alloys for large-scale complex structures.

Revealing the microstructure, texture evolution and mechanical properties along the whole wall of Mg-Gd-Y-Zn-Zr cylinders by tailoring rotary backward extrusion parameters

In this article, industrial-specification Mg-Gd-Y-Zn-Zr alloy cylinder parts were successfully prepared by rotary backward extrusion process. The microstructure distribution and mechanical properties evolution of the whole wall of different cylinder parts were investigated, and the effects of different rotation speeds on the microstructure and properties were also revealed. The results showed that the strain of the cylinder wall increased significantly with rotation speed increased, thereby generating a higher driving force for the microstructure refinement. The transformation of the inner wall progressed from the deformed zone (bulk-shaped long period stacking ordered (LPSO) phases, coarse deformed grains, and fine recrystallized grains) to the strongly affected zone (particle-shaped LPSO phases and fine recrystallized grains), with the latter expanding as rotation speed increased. Furthermore, there was a gradient distribution of strain in the cylinder walls, with the strain gradient intensifying alongside rotation speed. The transformation of the strongly affected zone into the deformed region from the inner to the outer wall suggested a diminishing effect of rotation speed on LPSO phases fragmentation and grain refinement. Notably, increasing rotation speed rendered improvements in the strength and ductility of the cylinder wall. And mechanical properties also displayed a gradient decrease from the inner wall to the outer wall. This variation in mechanical properties of different regions was closely associated with the contributions of grain boundary strengthening, texture strengthening and second phase strengthening.

Multi-regional microstructure control using ultrasonic-assisted directed energy deposition for Al-Cu alloy

The uneven microstructure and element distribution between the inner-layer zone (INZ) and the inter-layer zone (ITZ) resulting from the thermal cycling effect during the directed energy deposition process with the electric arc energy source (DED-Arc) can lead to inferior mechanical properties. In order to address this problem, the ultrasonic treatment of the 2319 Al-Cu alloy during the DED-Arc process is investigated to control the multi-regional microstructure quantitatively. Therefore, the effect of ultrasonic vibration during the DED-Arc process on grain morphology, distribution of precipitates and mechanical properties in different regions are explored in detail. The formation mechanism of differential microstructure is elucidated by using an ultrasonic-heat-flow coupling simulation model for the DED-Arc process. The results indicate that ultrasonic vibration refines the average grain size, leading to 16% and 40% reductions at the molten pool center (MPC) and boundary (MPB), respectively. However, the grains in the semi-melting zone (SMZ) experience coarsening due to the reduced temperature gradient after ultrasonic treatment. The enhanced melt flow rate is considered responsible for both the homogenization of Cu and the fragmentation of the θ-Al2Cu phase. The higher subgrain boundary density in the ITZ leads to an average microhardness of approximately 60 HV, which is lower than that found in the INZ (72.3 HV). Meanwhile, ultrasonic treatment increases the average strength and elongation by 38.1% and 17.5%, respectively, mainly through precipitation strengthening, which results in a strength increment of 91.6 MPa. The slip directions tend to be consistent after ultrasonic vibration, which is conducive to crystal sliding and displays excellent ductility.

Microstructural and mechanical properties of Al–Mg–Si–Cu joint fabricated by rotary friction welding

The correlation between the microstructural evolution and mechanical properties in different regions of Al–Mg–Si–Cu joint fabricated by rotary friction welding (RFW) has undergone a rigorous quantitative investigation using Vickers hardness evaluation, uniaxial tensile tests, electron backscatterred diffraction, X-ray diffractometry and transmission electron microscopy. The results of the investigation indicate that premature yielding and localized stress concentration inevitably occurred at the weakest heat affected zone (HAZ) region, remarkably compromising the mechanical properties of the joint. TEM observations revealed the presence of the rod-like Q′ phase and lath-like C phase within the BM and the pre-β″ phase in the weld zone, while no precipitate was identified in the HAZ on either sides. Although partial dynamic recrystallization occurred in HAZ reduced the grain size, extensive dislocation recovery and precipitate dissolving were two factors to be responsible for the lowest strength of the HAZ. On the contrary, fully recrystallization, severe plastic deformation and reprecipitation synthetically contributed to the strength recovery in the weld zone. Eventually, a model based on microstructural evolution that can quantitatively describe the observed strength difference in different regions is developed, suggesting that the major strength contributor is the dislocations strengthening, then the precipitation strengthening.

H13 tool steel fabricated by wire arc additive manufacturing: Solidification mode, microstructure evolution mechanism and mechanical properties

The critical application value of AISI H13 tool steel in the die and mold industry and the great application potential of additive manufacturing (AM) technology in die manufacturing and repair have attracted extensive attention from researchers. However, there is no consensus on the solidification mode and microstructure evolution mechanism of H13 during AM. The relationship between the unique cellular/dendritic substructures and the grain structures in AM-fabricated H13 components has yet to be fully understood. This work focused on the microstructure and mechanical properties of different regions of the H13 component manufactured by wire arc additive manufacturing technology. Thermodynamic calculations and experimental results confirmed the formation of δ-ferrite during the non-equilibrium solidification of AM. The cellular/dendritic substructure is caused by the solidification of δ-ferrite and austenite together with the accompanying segregation. The results of optical microscopy and scanning electron microscopy, as well as the reconstructed prior austenite grain structure by electron backscatter diffraction (EBSD) all confirmed that the formation and distribution of cellular/dendritic substructures were not directly related to the prior austenite grain. The EBSD pole figures show that although the martensite transformation weakened the preferred orientation of crystals, the martensite phase in the typical structure of the deposition area still had a high texture strength, which may be the main reason for the anisotropic mechanical properties of the H13 component.

Microstructure and mechanical properties of a directionally solidified superalloy DZ411 plate sample repaired by laser melting deposition

In this study, directionally solidified superalloy DZ411 plate samples were repaired with IN738LC superalloy using the laser melting deposition technique (LMD), and the cause for the variable mechanical properties in different regions of the samples was then investigated by quantitatively analyzing the microstructure of the repaired samples. Since the γʹ phase precipitation strengthening effect of the LMD region was inferior to that of the casting substrate region, the LMD region had a lower yield strength than the casting substrate region. However, the ductility and ultimate tensile strength of the LMD region were both superior to those of the casting substrate region due to finer grains and finer and more uniform carbides in the LMD region. Although the ductility and yield strength of the sample containing the heterogeneous interface of the two alloys were comparable to those of the casting substrate region sample, the tensile strength of heterogeneous sample was higher due to the generation of the geometrically necessary dislocation during heterogeneous interface deformation, which strengthened the heterogeneous sample. These results can serve as a reference for future LMD repair technology of directionally solidified superalloys.

An FDM-Based Dynamic Zoning Method for Disturbed Rock Masses above a Longwall Mining Panel

Underground longwall mining can seriously disturb the surrounding rock masses above the panel. A surface cracking zone, continuous deformation zone, fractured zone, and caved zone can be formed in the overlying strata (termed the “four zones”), which may further result in the spontaneous combustion of coal seams and water inrush. It is essential to study and predict the development characteristics of the four zones induced by longwall mining to guarantee mining safety. These four zones are developed during the mining process, and the mechanical properties in different regions correspondingly differ. Thus, the dynamic zoning characteristics of the disturbed rock masses should be considered in any simulations. In this paper, an FDM-based dynamic zoning method for disturbed rock masses above a longwall mining panel is proposed. This method is mainly composed of four stages: (1) establishing a simplified complete stress-strain curve; (2) determining the zoning criteria; (3) adaptively adjusting the mechanical parameters of the disturbed rock mass; and (4) numerically modeling the longwall mining based on the FDM. The proposed method was applied to a study site in the Taixi coal mine. The dynamic development process of the four zones induced by longwall mining was clearly observed in the modeling procedure. The numerical modeling results achieved in this work, including the periodical coal-seam roof caving and the dynamic development characteristics of the four zones, are consistent with the observed distribution and other studies. The heights of the caved and fractured zones are basically consistent with the empirical formula. Thus, the dynamic zoning method can analyze and predict the dynamic development characteristics of four regions.

Compositionally graded AlxCoCrFeNi high-entropy alloy manufactured by laser powder bed fusion

A high entropy alloy AlxCrCoFeNi (x = 0.07–0.88) coupon with a stepwise compositional gradation was fabricated by laser powder bed fusion (L-PBF) via in situ alloying of the blended metal powders. The chemical compositions, microstructures and mechanical properties of different regions of the coupon were examined to investigate the effect of Al content on the formation of different constituent phases. The maximum Al that can enable crack free printing was observed to be x = 0.5. Microstructural characterization indicates that grain morphologies, textures and phase variations in the graded alloys are closely related to x. Three phases were found across the graded coupon, i.e., face centered cubic (FCC), body centered cubic (BCC) solid solutions, and intermetallic B2. The phase variations can be attributed to the Al-induced lattice distortion and valence electron concentration. Further analysis suggests that the range of duplex FCC+BCC phases region is insensitive to cooling rates and could be mediated by formation of B2 phase. Nanoindentation studies show a steep increase in hardness along with the occurrence of BCC phase.

Tensile properties and damage mechanisms of compacted graphite iron based on microstructural simulation

Mechanical properties of compacted graphite iron (CGI) are substantially related to the microstructural contents and morphologies. To develop a simple and effective relation between graphite morphology and mechanical properties of CGI, a prediction method based on microstructual simulation is proposed in the present work. CGI slices are selected depicting the distribution of graphite spatial morphology. Tensile properties and damage mechanisms of microstructural slices are simulated with finite element (FE) method. By statistics of the graphite area fraction and vermicularity, it shows that 2D slicing scheme can reasonably depict the spatial morphology of 3D CGI microstructure. Tensile properties and damage mechanisms are further analyzed in slice results. A good agreement of the results is observed between experiment and simulation, which verifies the effectiveness of slice FE simulation. This research provides an effective way to estimate the mechanical properties of different regions in the large CGI components.

Inhomogeneous microstructure and mechanical anisotropy of multi-directional forged Mg-Gd-Y-Zn-Ag-Zr alloy

Abstract In this paper, through multi-directional forging with strain controlled multi-passes under the conditions of initial forging temperature of 480 °C and an accumulative strain of 4.4 after 27 forging passes, a bulky Mg-Gd-Y-Zn-Ag-Zr alloy with a size of 460 mm × 260 mm × 160 mm is prepared. The microstructure, texture and mechanical properties of different regions (the center, 1/2R and edge regions) in the alloy bulk are discussed. The results show that the material has undergone significant grain refinement during the multi-directional forging process. Due to the uneven strain and temperature distributions in different regions, inhomogeneous microstructures with different levels of dynamic recrystallization are formed. The average grain size of the center, 1/2R and edge regions is 2.91 ± 1.77, 3.83 ± 2.22, and 17.78 ± 12.24 μm, respectively. The center region exhibits a double-peak basal texture, while the 1/2R and edge regions additionally show a “rare earth texture component”. The tilt of the basal poles in some specific direction causes obvious mechanical anisotropy of the bulk. However, the non-basal rare earth texture component weakens the mechanical anisotropy. The optimum comprehensive mechanical properties are obtained in the center region, with the ultimate tensile strength of 364 MPa, the yield strength of 295 MPa, and the elongation to failure of 4.8%.

Microstructural evolution and its effect on mechanical properties in different regions of 2219-C10S aluminum alloy TIG-welded joint

Abstract Microstructural evolution and its effect on mechanical properties in different regions of 2219-C10S aluminum alloy tungsten inert gas (TIG) welded joint were analyzed in detail. In weld zone (WZ), α+θ eutectic structure formed at grain boundaries with no precipitates inside the grains. In partially melted zone (PMZ), symbiotic eutectic or divorced eutectic formed at grain boundaries and needle-like θ′ phases appeared in the secondary heated zone. In over aged zone (OAZ), the coarsening and dissolution of θ′ phases occurred and most θ′ phases transformed into θ phases. In general heat affected zone (HAZ), θ′ phases coarsened. Factors such as the strengthening phases, the grain size, the Cu content in matrix and the dislocation density can affect the mechanical properties in different regions of the joint. Moreover, a model describing the relationship between mechanical properties of the material and the volume fraction of precipitates, the average diameter of precipitates and the concentration of soluble elements was proposed.

Mechanical properties of the spinal cord and brain: Comparison with clinical-grade biomaterials for tissue engineering and regenerative medicine

Disorders affecting the central nervous system are a leading cause of disability in the world. Regenerative medicine using biomaterial-based therapies is a growing field that has potential application in the areas of spinal cord injury, neurodegenerative disorders and stroke. The mechanical properties of biomaterials implanted into the central nervous system are critical for effective integration with host tissue, but the biomechanical properties of the host tissue remain poorly characterised and assessing the stiffness of both soft biomaterials and central nervous system tissue remains challenging. Here, we describe a bespoke mechanical characterisation method that facilitates robust measurement of fresh spinal cord and brain tissue and allows direct like-for-like mechanical benchmarking for matching clinical-grade hydrogels suitable for regenerative medicine. We report differences in the mechanical properties of spinal cord tissue dependent on anatomical origin, regional variations in brain tissue stiffness, and quantify the extent of mechanical anisotropy within the cervical spinal cord. We then demonstrate that the mechanical properties of clinical-grade collagen, fibrin and alginate hydrogels can be tuned to closely mimic the mechanical properties of different regions within the central nervous system.

Investigation of processing–microstructure–property relationship using hot compression of a cone-shaped specimen

Gradient microstructure of the specimen was achieved by applying gradient thermoplastic deformation via electric resistance heating and hot compression of the cone-shaped specimen. A numerical modeling and experiment tests are conducted to investigate the microstructure evolution and mechanical properties in different regions of the specimen subjected to the gradient process parameters. Microstructure analysis revealed a direct relationship between the grain size and processing parameters. The temperature distribution on the gradient specimen ranges from about 800 to 1110 °C and equivalent strain along the axis of symmetry of the specimen section ranges from about 0.1 to 1.2. Under a temperature of 1050 °C and the equivalent strain of 0.7, the middle region of the specimen section has fine and equiaxed prior-austenitic grains with an average size of (27 ± 11) μm. Corresponding to the processing parameters, the lath martensite variants microstructure in this position with the highest hardness of (946 ± 17) HV. Consequently, the linkages among hot compression parameters, microstructure, and material properties of hardness are established via a high-throughput method in a cone-shaped specimen.

MR elastography frequency-dependent and independent parameters demonstrate accelerated decrease of brain stiffness in elder subjects.

To analyze the mechanical properties in different regions of the brain in healthy adults in a wide age range: 26 to 76years old. We used a multifrequency magnetic resonance elastography (MRE) protocol to analyze the effect of age on frequency-dependent (storage and loss moduli, G' and G″, respectively) and frequency-independent parameters (μ1, μ2, and η, as determined by a standard linear solid model) of the cerebral parenchyma, cortical gray matter (GM), white matter (WM), and subcortical GM structures of 46 healthy male and female subjects. The multifrequency behavior of the brain and frequency-independent parameters were analyzed across different age groups. The annual change rate ranged from - 0.32 to - 0.36% for G' and - 0.43 to - 0.55% for G″ for the cerebral parenchyma, cortical GM, and WM. For the subcortical GM, changes in G' ranged from - 0.18 to - 0.23%, and G″ changed - 0.43%. Interestingly, males exhibited decreased elasticity, while females exhibited decreased viscosity with respect to age in some regions of subcortical GM. Significantly decreased values were also found in subjects over 60years old. Values of G' and G″ at 60Hz and the frequency-independent μ2 of the caudate, putamen, and thalamus may serve as parameters that characterize the aging effect on the brain. The decrease in brain stiffness accelerates in elderly subjects. • We used a multifrequency MRE protocol to assess changes in the mechanical properties of the brain with age. • Frequency-dependent (storage moduli G' and loss moduli G″) and frequency-independent (μ1, μ2, and η) parameters can bequantitatively measured by our protocol. • The decreased value of viscoelastic properties due to aging varies in different regions of subcortical GM in males and females, and the decrease in brain stiffness is accelerated in elderly subjects over 60 years old.

Does photodynamic therapy with methylene blue affect the mechanical properties and bond strength of glass-fiber posts in different thirds of intraradicular dentin?

There are few studies on the influence of methylene blue as a photosensitiser on the mechanical properties and adhesion of glass-fiber posts to intraradicular dentin. Thus, this in vitro study aimed to evaluate the influence of photodynamic therapy with a methylene blue photosensitizer on the Martens hardness, elastic modulus, and bond strength of glass-fiber posts in different thirds of intraradicular dentin. Eighty bovine teeth were divided into the following five groups: a control using deionized water, and four other groups according to the methylene blue concentration (50 mg/L or 100 mg/L) and substrate treatment (with or without red laser action). Ultramicrohardness test was used to evaluate the mechanical properties in different regions of the root dentin (n = 8). Push-out analysis was evaluated using a universal testing machine (n = 8). Data were subjected to the Kruskal-Wallis test, followed by Dunn's test for comparing groups, and the Friedman test for comparing thirds (α = 0.05). Representative scanning electron microscopy images were obtained. In general, methylene blue in distinct concentrations, with or without laser action, did not cause differences in the mechanical properties or bond strength in different regions of root dentin (P > 0.05). Methylene blue at a higher concentration, activated with laser, produced lower bond strength values in the middle third of the root canal (P < 0.05). Methylene blue at 50 mg/L had no influence on the mechanical properties of the bovine tooth and the bond strength of the glass-fiber posts to intraradicular dentin.

A comprehensive study on the mechanical properties of different regions of 8-week-old pediatric porcine brain under tension, shear, and compression at various strain rates

Young porcine brain is often used as a surrogate for studying the mechanical factors affecting traumatic brain injury in children. However, the mechanical properties of pediatric brain tissue derived from humans and piglets are very scarce, and this seriously detracts from the biofidelity of the developed finite element (FE) models of the pediatric head/brain. The present study addresses this issue by subjecting the cerebrum (white matter and gray matter), cerebellum, and brainstem specimens derived from 8-week-old piglets to tension and shear testing at strain rates of 0.01, 1, and 50/s. The experimental data are combined with the corresponding data derived from a previous study under compression to obtain comprehensive stress-strain curves of the pediatric porcine cerebrum, cerebellum, and brainstem tissue specimens. In general, the average stress level of the white matter is somewhat higher than that of the gray matter under the tension, shear and compression conditions, however, this difference does not reach a significant level. The stiffness of the cerebellum and the cerebrum does not differ significantly under tension and shear conditions, but the stiffness of the cerebellum is greater than that of the cerebrum under compression. The brainstem has significantly higher stiffness than the cerebrum and the cerebellum under all loading modes. In addition, the mechanical properties of brain tissue exhibit significant strain-rate dependences. With increasing strain rate from 0.01/s to 50/s, the average stress at a strain of 0.5 for all of the brain tissue increased by about 2.2 times under tension, about 2.4 times under shearing and about 2.2 times under compression. The variations in the stress as a function of the strain rate for brain tissue specimens were well characterized by exponential functions at strains of 0.25 and 0.5 under all three loading modes. The results of this study are useful for developing biofidelic FE models of the pediatric brain.

Ratcheting Behavior of Weld Joints Under Uniaxial Cyclic Loading Using Miniature Specimen

Because of the size limitation of weld joints in different regions, the traditional standard bar specimen is not suitable to investigate the mechanical properties of weld joints. In this study, miniature specimens were extracted from specific regions (base metal, weld metal, and three heat-affected zones) of API X80 and X70 weld joints. Uniaxial tensile tests were conducted to obtain the mechanical properties of different regions, and then uniaxial ratcheting tests were conducted to investigate the ratcheting behaviors of the different regions under the same peak and nominal stresses. Under both the tensile tests and ratcheting tests, the weld joints exhibit heterogeneous results, such as different mechanical properties and ratcheting behaviors, which were region dependent. Furthermore, the yield strength and yield-to-tensile strength ratio contribute differently to the ratcheting response.

A study on mechanical and microstructural properties of dissimilar FSWed joints of AA5251–AA5083 plates

AbstractThis paper investigates the influence of rotational and travel speed on the structure and mechanical properties of different regions of friction stir welded dissimilar AA5251–AA5083 joints. It was observed that increasing rotational speed from 800 to 1 250 rpm, at a fixed travel speed, increased the grain size from 6.31 μm to 10.64 μm. This stemmed from higher heat input which is generated at higher rotational speed. Furthermore, it was discovered that at 1 000 rpm, 115 mm min−1 and also 1 250 rpm, 85 mm min−1, defect-free welds were produced. The results of tensile testing revealed that the best consistent tensile strength was produced at 1 000 rpm rotational speed and 115 mm min−1 travel speed with an average value of about 200 MPa. Further, the results clearly showed that the hardness values gradually increase from the 5251 aluminum side to the 5083 aluminum side.

Microstructure and mechanical properties of AZ80-Ag alloy processed by hot ring rolling

Hot ring rolling (HRR), a near-net-shape technology, was used to fabricate a large sized AZ80-Ag alloy ring at 653K in this study. The microstructure, texture and mechanical properties of different regions within the HRRed ring wall were systematically investigated. The lowest level of plastic deformation and highest temperature are identified in the central region of the ring wall. Due to the influence of nonuniform distribution of strain and temperature, the deformed microstructure is inhomogeneous throughout the ring wall thickness. After rolling deformation, the spherical β-Mg17Al12 precipitates are formed inside grains and along grain boundaries. The basal pole inclines and the {0001} orientation spreads towards some particular directions depending on the sampling regions. Therefore, obvious anisotropy of mechanical properties was observed in various regions due to different basal slip Schmid factors in the tensile directions.