Tensile Test Results Research Articles

Pulsed gas metal arc additive manufacturing of low-carbon steel: Microstructure observations and mechanical properties

Gas metal arc additive manufacturing (GMA-AM), also known as wire arc additive manufacturing (WAAM), uses an electric arc to melt a wire electrode and deposit objects layer by layer. This study focuses on creating single-pass wall structures using a low-carbon steel wire (ER70S-6) and examining the relationship between pulse frequency and weld geometry, microstructure, and mechanical properties. Microscopic observations showed a typical columnar microstructure with three distinct regions: acicular ferrite, bainite, and allotriomorphic ferrite in the first and last layers, while the mid-region exhibited homogenous polygonal ferrite grains with some pearlite at the grain boundaries. The tensile test results demonstrated a dependency of strength on the applied pulse frequency, with the highest strength (i.e., the ultimate tensile strength of 522 MPa and yield strength of 375 MPa with ductility of ∼52%) achieved in parts processed at a frequency of 100 Hz. Vickers microhardness values revealed uniform hardness in the middle region, consistent with the microstructure observation. Analyzing thermal cycles, coupled with microstructure analysis and continuous cooling transition diagrams, provided insight into how phase and microstructure evolution occurred in low-carbon low-alloy steels processed through PGMA-AM.

Test and analysis of the interfacial bond behaviour of circular concrete-filled wire-arc additively manufactured steel tubes

Interfacial bond behaviour of the circular concrete-filled wire-arc directed energy deposition (DED) steel tubes was investigated experimentally, in which wire-arc DED, commonly referred to as wire-arc additive manufacturing (WAAM), represents a metal 3D printing method. Firstly, a 3D laser scanning was employed to generate the 3D models of the WAAM steel components to obtain the geometric features. A parameter relating to the surface undulation was proposed to evaluate the roughness of the WAAM steel tubes. The results of tensile testing undertaken to obtain the mechanical properties of the WAAM material were summarised. Twelve push-out specimens were tested to obtain the load-slip response and bond strength, while the influence of surface undulation, diameter-to-thickness ratio and interface length was also assessed, respectively. The test results demonstrated that: 1) after reaching the peak load, a slowly descending region appeared until a relatively stable residual load was achieved; 2) the average bond stresses of the push-out specimens were greater than those of the push-out specimens fabricated by conventional steel tubes and even checkered steel tube. Comparisons of the bond strength of the push-out specimens against existing structural design standards indicated the design guidelines of various codes were quite conservative. There needs to consider the influence of the surface undulation of the WAAM steel tube. Finally, based on the nonlinear regression of the test data generated in the present study, an empirical equation was proposed for the prediction of the average bond strength for concrete-filled WAAM steel tubes.

Analysis of mechanical and water absorption properties of hybrid composites reinforced with micron-size bamboo fibers and ceramic particles

Abstract Bamboo and its hybrid composites were made using the hand lay-up method to evaluate the change in mechanical and physical properties that occurred through filler addition. Density measurements and tensile test results showed an increment in values when a certain percentage of silicon carbide (SiC) was added. As the SiC percentage grows from 0 to 6 %, the density of the hybrid composite increases from 1.15 to 1.36 gm/cc whereas tensile strength increases from 37 MPa to 42 MPa when 4 wt% SiC is added in 20 wt% of the bamboo composite. The scanning electron microscopy (SEM) analysis of tensile fractured samples further supported the improvement in tensile characteristics. To examine the impact and hardness characteristics, composites were subjected to the Charpy impact test and hardness test. 4 wt% of SiC addition in 20 wt% of the bamboo composite decreased the impact strength from 28.79 to 27.43 (×10−3 kJ/m2) and increased the hardness from 44 to 55 Hv. The composites’ water absorption behavior demonstrated that the addition of filler lifts the composite’s resistance to absorbing water, preserving the composites’ dimensional firmness and mechanical qualities.

Theoretical and Experimental Investigation of 3D-Printed Polylactide Laminate Composites' Mechanical Properties.

The purpose of this work is to theoretically and experimentally investigate the applicability of the Tsai-Hill failure criterion and classical laminate theory for predicting the strength and stiffness of 3D-printed polylactide laminate composites with various raster angles in mechanical tests for uniaxial tension and compression. According to the results of tensile and compression tests, the stiffness matrix components of the orthotropic individual lamina and strength were determined. The Poisson's ratio was determined using the digital image correlation method. It was found that the Tsai-Hill criterion is applicable for predicting the tensile strength and yield strength of laminate polymer composite materials manufactured via fused deposition modeling 3D printing. The calculated values of the elastic moduli for specimens with various raster angles correlate well with the values obtained experimentally. In tensile tests, the error for the laminate with a constant raster angle was 3.3%, for a composite laminate it was 4.4, in compression tests it was 11.9% and 9%, respectively.

Effects of Tremella polysaccharide on frost resistance of frozen dough considering water state, physical property and gluten structure

To explore the effects of Tremella polysaccharide (TP) on frost resistance in dough, different concentrations of TP (0, 0.2, 0.4, 0.6, 0.8, and 1.0 %) were added to frozen dough, and the effects on the water state, physical property, and gluten structure of the dough were studied. The results showed that 0.6 % TP concentration caused a reduction in the freezable water content and growth rate of free water, and inhibited the recrystallization of ice in dough during frozen storage. The tensile test and rheological analysis results showed that 0.6 % TP concentration could significantly protect the tendons of dough and thus maintain its dominant elasticity. Free sulfhydryl group content determination and infrared spectrum scanning confirmed that 0.6 % TP concentration yielded the lowest transition of the ordered structure to a disordered structure in the dough and maintained the integrity of the dough gluten structure with minimal porosity. These findings indicate that TP can be used as a potent food cryoprotectant to mitigate the deterioration of frozen dough quality and has promising application prospects in the food industry.

Optimization in the reprocessing of recycled polyamide 6 reinforced with 30 wt% Glass Fiber (PA6/GF30) using mixture design

AbstractIn the present study, polyamide 6 reinforced with 30 wt% Glass fiber (PA6/GF30) used in automotive industry was reprocessed via injection molding. The virgin and recycled PA6/GF30 samples were characterized by chemical, rheological, mechanical, and morphological properties as a function of the number of processing cycles. After each reprocessing cycle, a decrement in mechanical properties in tensile, bending, and impact strength was revealed for different combination of cycle number (N0 [for the virgin PA6/GF30], N1 [for the first recycled PA6/GF30], N2 [for the second recycled PA6/GF30], and N3 [third recycled PA6/GF30 sample]) in the composite mixture. A simplex‐centroid mixture design (SCMD) was used to evaluate the effect of combining Ni (i=0,1,2) on the mechanical properties of composite samples for optimization. Graphical comparison of experimental results using regression models showed a high degree of correlation. Results revealed that the ternary N0N1N2 blends composite made up of 67.97 wt% N0, 23.13 wt% N1, and 8.89 wt% N2 exhibited the best mechanical properties. Furthermore, a good correlation between the scanning electron microscopy (SEM) observations and tensile test results was observed. Hence, the new reprocessed formulation presents a cost‐effective alternative of virgin PA6/GF30 for different engineering applications.

Effect of Heat Treatment on the Microstructure and Mechanical Properties of the Al0.6CoCrFeNi High-Entropy Alloy.

The effect of heat treatment on the microstructure and tensile properties of an as-cast Al0.6CoCrFeNi high-entropy alloy (HEA) was investigated in this paper. The results show that the as-cast Al0.6CoCrFeNi HEA presents a typical FCC dendrite morphology with the interdendritic region consisting of BCC/B2 structure and heat treatment can strongly affect the microstructure and mechanical properties of HEA. Microstructure analysis revealed the precipitation of a nano-sized L12 phase in the FCC dendrite and the formation of the FCC and σ phases in the interdendritic region after annealing at 700 °C. The coarse B2 phase was directly precipitated from the FCC dendrite in the 900 °C-annealed sample, with the coexistence of the B2, FCC, and σ phases in the interdendritic region. Then, the interdendritic region converted to a B2 and FCC dual-phase structure caused by the re-decomposition of the σ phase after annealing at 1100 °C. The tensile test results show that the 700 °C-annealed HEA presents the most significant strengthening effect, with increments of corresponding yield strength being about 107%, which can be attributed to the numerous nano-sized L12 precipitates in the FCC dendrite. The mechanical properties of 1100 °C-annealed alloy revert to a level close to that of the as-cast alloy, which can be attributed to the coarsening mechanism of B2 precipitates and the formation of a soft FCC phase in the interdendritic region. The observed variation in mechanical properties during heat treatment follows the traditional trade-off relationship between strength and plasticity.

Research on property and burning behavior of flammable casing for underground coal gasification

In this work, the comprehensive properties of flammable casing for underground coal gasification is systematically investigated, including flammable casing material physical, chemical and mechanical properties and full-size flammable casing mechanical properties and burning behavior. The flammable casing material consists of magnesium alloy matrix and rare earth particles, thermal conductivity and expansion property of which are weak. Results of high-temperature tensile test reveal that flammable casing material has good high temperature strength which declines by 30 % at 300 °C. Corrosion rate of flammable casing material is relatively high without extra protection. The full-size flammable casing possesses considerable mechanical property, thread property and high temperature collapse resistance. Burning of flammable casing is safe and stable. Burning rate of flammable casing material can be effectively controlled by water flow. Combustion product of flammable casing presents powder condition, which has no risk of blocking the gasification channel. To sum up, flammable casing is necessary to the realization of underground coal gasifying process, which plays the significant role of the development and application of underground coal gasification technology.

Study of hot tensile deformation behavior and microstructure characteristics of Zn-22Al microtubes using direct resistance heating-assisted tensile tests

To explore the deformation behavior of Zn-22Al alloy microtubes during hot forming processes with rapid heating, direct resistance heating (RH)-assisted tensile tests using microtubes are introduced based on their quick and easy temperature control. Notably, the large temperature difference of the sample during the RH-assisted tensile tests affected the accuracy of the tensile test results. To perform the RH-assisted tensile tests of the microtubes correctly, the specimens were designed with optimized structures of effective and total lengths of 30 and 60 mm, respectively. Better ductility was observed in the microtube drawn at 200 °C owing to the highly activated grain boundary sliding (GBS) caused by its uniform finer grain structure, greater high-angle grain boundary (HAGB) densities in the close-to-fracture area, and intergranular ductile fracture mode. The primary deformation mechanism of the microtube during hot forming was built based on hot tensile behavior, microstructure, and fracture surface analysis. It was also demonstrated that there is an intrinsic relationship between the temperature distribution, change in the microstructure of different parts, and multiple necking phenomena of the microtube formation process.

Synthesis of non‐isocyanate polyurethanes with high‐performance and self‐healing properties

AbstractDue to the utilization of the potentially hazardous monomer, isocyanate compound, polyurethanes (PUs) with good properties are restricted in several fields, such as bio‐engineering. Non‐isocyanate polyurethanes (NIPUs) with high overall performance and self‐healing properties were synthesized by dicarbamate, bio‐based isosorbide (IS) and polycarbonate diols (PCDLs) through a solvent‐free and ecologically friendly melt polycondensation route. Previously, few bio‐based monomers have been introduced into polycondensation reactions of PUs. Chemical structures of NIPUs were analyzed by Fourier transform‐infrared spectroscopy (FT‐IR), proton nuclear magnetic resonance (1H NMR) and gel permeation chromatography (GPC). With changing the IS content and the molecular weight of PCDL, the obtained NIPUs had linear structures and high molecular weights ranging from 3.3 × 104 to 5.9 × 104 g/mol. Results of tensile testing, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) suggested NIPUs had well thermal and mechanical properties, with Td,5% above 286.2°C and tensile strength between 8.0 and 16.7 MPa due to the crystallization and the hydrogen bonding interactions. Furthermore, the NIPUs exhibited self‐healing ability and recyclability, having great potential for industrialization.

Microstructure and mechanical property of Ti/Cu ultra-thin foil lapped joints with different weld depths by nanosecond laser welding

In present study, 50 μm thick Ti/Cu pure metal ultra-thin foils are successfully lap-welded by a nanosecond fiber laser. The joints with adjustable depths are obtained by controlling the laser energy input precisely. The microstructure and mechanical properties of Ti/Cu joints with different depths are well analyzed, respectively. In the joint with smaller penetration depth of 10 μm, thin band-like Ti/Cu intermetallic compounds (IMCs) are formed, while in the joint with a larger penetration depth of 40 μm, thicker band-like Ti/Cu IMCs and sizable bright dendritic Ti2Cu phases are formed, since more Cu element are involved in the chemical reaction in the joint with penetration depth increasing. The tensile test results show that the weld with 10 μm penetration depth has the best tensile strength up to 240 MPa, which is mainly due to less IMCs and low heat input in the weld. In addition, the fracture mode of the joint is classified into two models, including brittle quasi-cleavage fracture on the Ti side fusion zone (FZ) and ductile fracture on the Cu heat affected zone (HAZ), respectively, depending on the penetration depth above or below 30 μm.

Adhesion and Sliding Constitutive Relationship between Basalt–Polypropylene Hybrid Fiber-Reinforced Concrete and Steel Bars

The extreme marine environment of the South China Sea Islands, which features high temperatures, high humidity levels and high salt levels, seriously affects the safety of building structures. The durability of concrete can be significantly improved by adding a basalt–polypropylene hybrid fiber, but its bonding mechanism with deformed bars is complicated. Therefore, the bonding performance of hybrid basalt–polypropylene fiber-reinforced concrete and deformed bars was studied by combining experiments and a theoretical analysis. We designed 38 groups of different concrete strengths, different thicknesses of concrete covers, different anchor lengths and different diameters of rebars. The bond strengths, bond–sliding curves and failure forms of each pull specimen were compared and analyzed. The results showed that the failure forms and bond–slip curves of the basalt–polypropylene hybrid fiber-reinforced concrete specimens and the ordinary concrete specimens were essentially the same. Based on the results of the axial tensile tests, an ultimate bond strength prediction model was developed, and a bond–sliding constitutive model for hybrid fiber-reinforced concrete and steel bars was also established.

Creep damaged microstructure and mechanical properties of Cr–Mo–V steel subjected to long-term service exposures

Evaluating the degree of creep damage is of high importance for the residual life assessment of high temperature and pressure steam piping systems of power plants. This study aims at assessing creep damaged microstructure and mechanical properties of low alloy Cr–Mo–V steel after long-term service exposures. Variations in mechanical properties have been assessed by means of tensile tests, hardness measurement and instrumented indentation testing (IIT). Optical and scanning electron microscopies were employed for the identification of creep damaged microstructure. The effect of heat treatment on the recovery of microstructure and mechanical properties was also studied. Correlations of IIT and hardness results between surface and bulk values have been obtained. The results of IIT agree well to the results of tensile tests. Moreover, relationships between hardness and tensile properties have been assessed. Eventually, the evaluation of the degree of creep damage by employing IIT and hardness measurement was attempted.

Segmental biomechanics of the normal and glaucomatous human aqueous outflow pathway

The conventional aqueous outflow pathway, encompassing the trabecular meshwork (TM), juxtacanalicular connective tissue (JCT), and inner wall endothelium of Schlemm's canal (SC), governs intraocular pressure (IOP) regulation. This study targets the biomechanics of low-flow (LF) and high-flow (HF) regions within the aqueous humor outflow pathway in normal and glaucomatous human donor eyes, using a combined experimental and computational approach. LF and HF TM/JCT/SC complex tissues from normal and glaucomatous eyes underwent uniaxial tensile testing. Dynamic motion of the TM/JCT/SC complex was recorded using customized green-light optical coherence tomography during SC pressurization in cannulated anterior segment wedges. A hyperviscoelastic model quantified TM/JCT/SC complex properties. A fluid-structure interaction model simulated tissue-aqueous humor interaction. FluoSpheres were introduced into the pathway via negative pressure in the SC, with their motion tracked using two-photon excitation microscopy. Tensile test results revealed that the elastic moduli of the LF and HF regions in glaucomatous eyes are 3.5- and 1.5-fold stiffer than the normal eyes, respectively. The FE results also showed significantly larger shear moduli in the TM, JCT, and SC of the glaucomatous eyes compared to the normal subjects. The LF regions in normal eyes demonstrated larger elastic moduli compared to the HF regions in glaucomatous eyes. The resultant strain in the outflow tissues and velocity of the aqueous humor in the FSI models were in good agreement with the digital volume correlation and 3D particle image velocimetry data, respectively. This study uncovers stiffer biomechanical responses in glaucomatous eyes, with LF regions stiffer than HF regions in both normal and glaucomatous eyes. Statement of significanceThis study delves into the biomechanics of the conventional aqueous outflow pathway, a crucial regulator of intraocular pressure and ocular health. By analyzing mechanical differences in low-flow and high-flow regions of normal and glaucomatous eyes, this research unveils the stiffer response in glaucomatous eyes. The distinction between regions' properties offers insights into aqueous humor outflow regulation, while the integration of experimental and computational methods enhances credibility. These findings have potential implications for disease management and present a vital step toward innovative ophthalmic interventions. This study advances our understanding of glaucoma's biomechanical basis and its broader impact on ocular health.

The elasto-plastic numerical study of crack initiation in notched PMMA specimens under uniaxial loading conditions – Tension and torsion

This paper presents the results of FEM numerical calculations aimed at describing the plastic strain and stress fields under critical loading conditions: tensile force or torsional moment. The calculations were carried out with reference to the results of experimental tensile and torsional tests of flat PMMA specimens weakened with V-notches of different root radii: 0.5, 2 and 10 mm. The procedure for conducting nonlinear numerical analyses is described, including the determination of the actual hardening curve by the hybrid method. A high level of consistency between the results of the experimental and numerical calculations was obtained through description of PMMA with the elastic–plastic material model. The points of occurrence of stress maxima and plastic strain were indicated, which were taken as potential crack initiation sites. On the basis of the stress and plastic strain values measured at the critical points, a stress–strain fracture criterion was formulated, which was then positively verified.

Experimental and analytical investigation of the tensile behavior of 3D-printed composites based on micro-CT analysis

Mechanical properties of short fiber reinforced composites manufactured with fused deposition modeling is affected by variables such as printing properties and internal structure of the composite. In this study, the relation between the tensile properties of 3D-printed short fiber reinforced composites, printing orientation and internal structure is inspected. Samples of different printing orientations are manufactured. These samples are inspected under X-ray micro computed tomography (micro-CT) and their fiber orientation distributions and fiber properties are determined. Then, these internal structure properties are applied to analytical material models to estimate the tensile properties of composites. Estimated material properties are compared with tensile test results. It turns out that analytical models that consider internal structure properties provide more accurate estimations than other analytical models that does not take these into account.

Structure and Mechanical Properties of Milled and 3D-Printed Ti-6Al-4V Alloys for Subtractive and Additive CAD/CAM Manufacturing in Dentistry

The mechanical properties, structure, and morphology of milled and 3D-printed Ti-6Al-4V alloys produced by selective laser melting were investigated in this study. The mechanical properties were investigated by means of nanoindentation, a tensile test, and a three-point bending test. An Atomic Force Microscope (AFM) was used to study the surface topography and roughness of both titanium alloys. The surface structure and phase analyses were studied by a scanning electron microscope (SEM) and through powder X-ray diffraction (XRD). The results from the nanoindentation experiments showed that the 3D-printed sample has higher indentation hardness and modulus than the milled one. The AFM observation of the surface topography of the samples showed that the milled sample has a higher roughness than the 3D-printed one. The tensile test results showed that the 3D-printed sample by means of Selective Laser Melting (SLM) technology has about 26% higher tensile strength and smaller elongation than the milled one. The three-point bending test revealed that the 3D-printed Ti-6Al-4V sample has higher flexural strength than the milled one. It was found that the 3D-printed sample has a smaller crystal size than the milled one, which, according to the Hall–Petch relationship, leads to its higher indentation hardness.

Microstructure and properties in CuCrZr alloy fabricated by selective laser melting with different heat treatment

CuCrZr alloy is promising in many industrial applications because of its extremely high thermal conductance and conductivity. In this paper, the effects of aging heat treatment temperature and time on microstructure and mechanical properties of CuCrZr alloy fabricated by selective laser melting were investigated. The mechanical properties of CuCrZr alloy after aging heat treatment were investigated by high temperature tensile experiments. The results showed that the aging treatment did not change the grain size and morphology of CuCrZr alloy. Scanning electron microscope (SEM) and transmission electron microscope (TEM) observation showed that Cr precipitated in the microstructure after aging treatment and caused precipitation strengthening, which is an important factor for the mechanical properties of CuCrZr alloy manufactured by SLM. After aging heat treatment, the hardness of CuCrZr alloy increases to 185.7 ± 1.82HV. Tensile test results show that aging heat treatment can greatly improve the tensile strength of CuCrZr fabricated by SLM, and the maximum value is 515.5 ± 12.8 MPa. At the same time, the tensile property of CuCrZr alloy decreases with the increase of temperature, but can still reach 319.34 ± 0.49 MPa at 250 ℃.

The anisotropy of fracture toughness of an α+β titanium alloy by β forging

This study aims to investigate the anisotropic fracture toughness of an α+β titanium alloy processed by β forging. A typical basket-weave microstructure is observed, including the primary α (αp) phase, micron-scaled secondary α (αs) phase and residual β phase. The tensile test results show that the anisotropic strength results from the fine grain strengthening as well as the texture strengthening, and the plasticity difference is determined by the normal stress acting on the main crack in the fracture process. The orientation of the specimen also has a significant impact on fracture toughness. The corresponding toughening models of underlying damage mechanism with different orientations are proposed and discussed. It is found that the internal toughening mechanism is dominant, and external toughening mechanism also plays an important role in fracture toughness, including delamination and crack deflection caused by elongated β grains arrangement. Finally, the differences of J-integral resistance curves with different orientations are investigated in detail. The strength and fracture toughness values, KJIC (crack-initiation toughness) and KSS (growth toughness), are both highest when loading along radial direction (RD), and the positive effects of β grain morphology and two-phase texture on anisotropy of KJIC are summarized.

Effect of Superheat on Microstructure and Mechanical Properties of Al-7Si-2Fe Alloy

Recycling of aluminum (Al) alloys is critical to meet the demands of global net zero emission targets. The major challenge in the recycling of Al alloys is the presence of a higher content of iron as an impurity in Al alloy scraps, which deteriorates the mechanical properties of recycled alloys. In the present work, Al-7%Si alloys and Al-7%Si-2Fe alloys were cast at three different superheat temperatures to study the effect of superheat on the formation of iron intermetallic particles in these alloys. Microstructure–mechanical properties correlations were carried out using SEM-EDS and tensile testing of the alloys. 3D x-ray computed tomography (XCT) results show that the β-phase intermetallic particles were observed to be large and platelet-shaped in the Al-7Si-2Fe alloy cast at 700°C, while these particles appeared to be finer and uniformly distributed throughout the sample in the alloy cast at 900°C. XCT results show the presence of large shrinkage porosity in the Al-7Si-2Fe alloy cast at 700°C, due to the presence of large intermetallic particles which hinder the flow of molten metal during solidification of the alloys. Tensile test results show that the addition of 2% iron resulted in a significant reduction in the elongation of the alloy at all superheat temperatures.