Tensile Specimens Research Articles

Surrogate model-based assessment of particle damage behaviour of Al[sbnd]Zn[sbnd]Mg alloy

Recent research has found some intermetallic compound particles with even stronger hydrogen trapping capacity (e.g., Al7Cu2Fe) than the age-hardening precipitates that are reported to be the origin of hydrogen embrittlement in aluminium. Such intermetallic compound particles can reduce hydrogen concentration at the interface between the precipitates and aluminium by absorbing hydrogen in their interiors, thus preventing the hydrogen embrittlement of aluminium. However, this cannot be achieved if the particles, which have absorbed large amounts of hydrogen, are damaged due to hydrogen embrittlement. In this study, the hydrogen embrittlement of aluminium was observed in situ by X-ray CT, and the damage behaviour was analysed of all the particles that were located in the gauge section of a single tensile specimen. After exhaustive quantification of the size, shape, and spatial distribution of the particles, coarsening processes identified highly correlated design variables. Subsequently, particle damage behaviour was analysed utilizing a surrogate model using a support vector machine. The damage to Al7Cu2Fe particles could be described only by design variables representing size and shape, while those representing spatial distribution were removed through the coarsening processes. No change was observed in the damage behaviour of Al7Cu2Fe particles with increasing hydrogen concentrations, and it was concluded that the dispersion of Al7Cu2Fe particles is effective in preventing hydrogen embrittlement of aluminium. The contribution of damaged particles to the formation of fracture surfaces and the damage behaviour of Mg2Si particles, where damage is accelerated by hydrogen, were also analysed.

The crack propagation behaviors, microstructure and mechanical properties of T-welded joints for TIGW with crystal plasticity model and XFEM

In view of the significant impact of welding defects on the fracture behaviors involving the strength, stress concentration and bearing capacity of welded joint, etc., the propagation behaviors and mechanical properties of welded joints with porosity and micro crack are deeply investigated using a multiscale method. In this work, a crack nucleation and propagation model based on crystal plasticity theory, combined with the extended finite element method (XFEM), is established for the T-welded joint. The maximum slip on the predominant slip system method is applied to predict the crack propagation path of pores and micro cracks in the weld zone (WZ), and the effect of crystal orientation on crack growth is explored. Then, a continuous model is used to analyze the micro and macro fracture behaviors near the weld under tensile load, combined with the maximum principal stress method. The WZ and heat affected zone (HAZ) are observed using electron backscatter diffraction (EBSD) to study the microstructure evolution. Considering grain boundaries, the image information of crystal morphology is processed through binary image analysis for FE modeling. The local mechanical properties testing is carried out using micro-specimens of HAZ and WZ to calibrate the crystal plastic parameters. The results show that the resolved shear stress of the predominant slip system of crack initiation and propagation elements is increased by pore and crack defects. The fracture positions of tensile specimens through numerical simulation are in good agreement with the macroscopic experimental results. It will provide an analysis basis for preventing fracture failure and improving the service performance of thin-walled structures in future.

Experimental and theoretical studies on 3D printed short and continuous carbon fiber hybrid reinforced composites

3D-printed carbon fiber composites hold significant potential in aerospace applications because of their lightweight, high strength and complex structure fabrication capabilities. However, additive manufacturing characteristics such as high porosity, anisotropy and continuous fiber content significantly affect the mechanical properties of printed parts. The aim of this study is to investigate the influence of hybrid printing of short and continuous carbon fibers on the mechanical properties and failure mechanisms of composites and to develop a model to predict elastic properties considering porosity. First, mechanical testing and characterization of short and continuous fiber reinforced polyamide (nylon) print filaments are performed. The results indicate that the elastic modulus and ultimate strength of continuous carbon fiber filaments reach 60 GPa and 1500 MPa, respectively, while the strength and elastic modulus of short carbon fiber filaments reach 60 MPa and 1 GPa, respectively. Then tensile specimens with different continuous fiber orientations and different continuous fiber placement sequences are printed and tested using a multi-material 3D printing technique. The specimens are characterized before and after testing using scanning electron microscopy and microscopy to assess the porosity and failure mechanisms of specimens with different configurations. The results show that the mechanical properties of the printed parts are much lower than those of the print filaments, which proves the serious negative impact of the material extrusion process on the mechanical properties of the printed structural parts. Finally, an analytical method for predicting the elastic behavior of printed composites is developed by introducing the porosity factor in the volume-averaged stiffness model. For continuous and short fiber filled composites with different fiber contents and printing orientations, the predicted results are in agreement with the experiments, and the prediction error is greatly reduced from 30 % to <5 %.

Excellent low temperature superplasticity and its deformation mechanism in nano/ultrafine grained Fe–17Cr–6Ni stainless steel

Superplastic deformation typically occurs in non-ferrous metals at high temperatures, which results in severe surface oxidation and high energy consumption. In this study, we designed and manufactured a nano/ultrafine-grained stainless steel with a dual-phase microstructure that exhibits excellent low-temperature superplastic deformation capability. A maximum tensile elongation of approximately 500% was achieved when the tensile test was conducted at 700 °C with an initial strain rate of 5 × 10⁻⁴ s⁻1. Even after a 500% tensile elongation, the austenite grains in the gauge section of the tensile specimen still maintained an equiaxed grain shape, and the texture also weakened significantly, indicating that grain boundary sliding and grain rotation dominated the deformation process during superplastic flow. The outstanding superplasticity is mainly attributed to the dual-phase microstructure composed of nano/ultrafine austenite grains and martensite.

Comparative evaluation of vat photopolymerization and steel tool molds on the performance of injection molded and overmolded tensile specimens

AbstractThis study explores the use of vat polymerization stereolithography (SLA) for fabricating mold tooling, subsequently utilized in injection molding (IM) and overmolding of tensile specimens and directly compared to those produced using metal molds. The results first find the manufacturing time for an SLA‐fabricated mold is remarkably short, approximately 6 h, presenting a substantial improvement over traditional methods. Mechanical testing revealed that the tensile specimens from the SLA‐fabricated molds exhibited the highest tensile strength among all overmolding batches. This performance was consistent with the tensile bars produced using metal molds, demonstrating the viability of SLA‐fabricated molds for overmolding applications and highlighting the potential of FDM to customize the properties of final products. However, variations in mold types impacted the dimensional tolerance and tensile strength of the final specimens. Metal mold‐fabricated tensile bars exhibited superior dimensional accuracy and maximum tensile strength (50.6–61.7 MPa) compared to those produced with SLA‐fabricated molds (46.9–55.9 MPa). These differences are attributed to the rougher surface finish inherent to the layer‐by‐layer construction of SLA and the internal stresses and defects resulting from lower thermal conductivity and uneven cooling. In conclusion, this study underscores the promising future applications of SLA‐fabricated molds in overmolding, offering reduced manufacturing costs and enhanced design freedom. The findings support the potential of SLA to revolutionize mold fabrication, thereby extending its utility and optimizing the production of polymer components with customized properties.Highlights SLA molds compared to metal molds for direct injection molding and overmolding. FFF preforms with varied geometries were overmolded to finalize the specimens. Joint configurations in overmolding improved tensile performance. Overmolding showed better dimensional accuracy than FFF specimens. SLA mold preparation significantly reduced manufacturing costs.

Tension fracture delamination analysis on a hot rolled Nb-bearing high-strength steel for vehicle wheel application

A comparative analysis was conducted on post-tensile specimens with and without delamination to investigate the causes of tensile delamination in hot rolled steel with a 600 MPa ultimate tensile strength (UTS) for automotive wheel applications. The tensile specimens were sampled from the hot rolled coils in the transverse direction per ASTM A370 standards, and Tensile tests were performed at room temperature with a constant crosshead speed of 0.5 mm/min. The results indicate that normal segregation is not the sole factor contributing to delamination; rather, the presence of Nb lumps within the central segregation area increased the susceptibility to tensile delamination. The statistical analysis indicates that there is a more intense presence of Nb lumps in specimens with tension delamination, tension delamination will occur during specimen stretching when there are Nb lumps with an average size greater than 6.5 μm and a quantity greater than 3 in the central segregation region. Meanwhile, the sources of lumps are also analyzed indicates that these Nb lumps originate from the ferroniobium alloy added during BOF tapping and ladle refining.

Investigating the influence of 3D printing parameters on the mechanical characteristics of FDM fabricated (PLA/Cu) composite material

This investigation elucidates the impact of 3D printing parameters, encompassing the infill pattern variations (cross, grid, line, triangle, and tri-hexagon) and infill percentages (10%, 30%, 50%, 70%, and 90%), on the mechanical behavior of the PLA/Cu composite. A 3D model of the tensile specimen was designed in accordance with the ASTM D1708 standard and subsequently printed using carefully chosen printing parameters. Subsequent to fabrication, the samples were subjected to tensile testing. Scanning Electron Microscopy (SEM) imaging, along with Energy-Dispersive X-ray (EDX) analysis, was carried out for the fabricated specimens. Additionally, SEM analysis was performed on the fracture surface of the specimens. Tensile tests were performed on all printed samples, encompassing various patterns and infill percentages. The resulting tensile data were analyzed and discussed with a focus on parameters such as toughness, ultimate tensile strength (UTS), Young's modulus, and strain at UTS. The maximum UTS observed was 13.69 MPa, occurring in specimens with a line pattern at an infill density of 90%. In contrast, the minimum UTS recorded was 4.5 MPa for samples utilizing a triangle pattern at 50% infill density. The highest Young’s modulus measured, 275.6 MPa, was achieved with the line pattern at 90% infill density, whereas the lowest recorded Young’s modulus, 92 MPa, was associated with the triangle pattern at 10% infill density. Furthermore, the maximal strain at UTS (30%) was exhibited by the tri-hexagonal pattern at 50% infill density, while the minimal strain (10%) was observed in the line pattern at 70% infill density.

Corrosion of aluminium alloy AA2024-Τ3 specimens subjected to different artificial ageing heat treatments

The effect of artificial-ageing on corrosion behaviour of aluminium alloy (AA)2024-T3 was investigated. The natural ageing which takes place during the aircraft's lifespan was simulated with isothermal heat-treatments at 190 °C. Electrochemical impedance spectroscopy measurements were performed in different heat-treated specimens to examine the prevailing corrosion mechanisms. Additionally, pre-corroded tensile specimens from different heat-treatment conditions were mechanically tested to assess the corrosion-induced degradation. Different forms of corrosion were revealed in the investigated ageing tempers; intense localized attack was noticed in the initial (T3) and under-aged (UA) tempers. UA condition exhibited the highest susceptibility to corrosion propagation followed by T3, according to the charge transfer resistance RCT and degradation rate of tensile elongation at fracture Af ( ≈ 0.118) and ( ≈ 0.103), respectively. Corrosion-induced degradation rates for the peak-aged (PA) and over-aged (OA) tempers ( ≈ 0.042 and 0.054, respectively) were almost one third of UA, attributed to volume fraction and size of the precipitated second-phase particles.

Optimization of friction stir processing parameters to improve mechanical properties and microstructure of Al5083 aluminum alloy reinforced with AlCoCrFeNiSi high-entropy alloy

Abstract This study explores integrating AlCoCrFeNiSi high-entropy alloy (HEA) particles into the Al5083 aluminum alloy matrix via Friction Stir Processing (FSP) to enhance mechanical characteristics. Microstructural analysis reveals a homogeneous distribution and size reduction of HEA particles, contributing to improved structural strength. X-ray diffraction (XRD) examination confirms the formation of solid solution phases in the HEA particles, validating their role in enhancing material properties. Through the utilization of Design of Experiments (DOE) and Response Surface Methodology (RSM), FSP parameters are systematically optimized, enabling precise predictions of mechanical behavior. Multi-response optimization identifies the optimal combination of FSP parameters, resulting in significant enhancements in Ultimate Tensile Strength (UTS) and Hardness, reaching 314 MPa, 42% elongation, and 75 HV, respectively. Scanning Electron Microscopy (SEM) analysis of tensile test specimens elucidates the impact of varied FSP parameters on microstructural features, emphasizing the importance of optimal mixing for improving interfacial bonding and mechanical properties. This study underscores the effectiveness of integrating HEA particles and optimizing FSP parameters to elevate the mechanical properties of Al5083 aluminum alloy, paving the way for tailored composite materials with enhanced performance for specific applications.

Microstructure and mechanical properties of 1 mm thin plate TC4 titanium alloy joint by ring laser welding

Abstract Ring laser welding was used to weld 1 mm thin plates TC4 titanium alloy, and the effects of different ring laser powers on the microstructure and mechanical properties of the weld were studied. The results indicate that the microstructure in the weld zone under different powers all contain basket structures, although the morphology of the martensite within the baskets differs. The microstructure in the weld zone is mainly composed of acicular α′ martensite, secondary α phase, and residual β phase. The microstructure in the heat-affected zone of the weld is mainly composed of acicular α′ martensite, initial α phase, secondary α phase, and residual β phase. The hardness of the weld is higher than that of the base metal, showing an overall trend of first increasing, then decreasing, and then increasing again before decreasing. The tensile specimens under different powers all fractured in the heat-affected zone of the weld, and the type of fracture is quasi-cleavage. At a laser power of 900 W, the weld has good formation, with minimal spatter on the surface, and good weld penetration. The microstructure of the weld is mainly composed of acicular α′ martensite, initial α phase, secondary α phase, and residual β phase. The hardness of the weld is 387.76 HV. The tensile strength and elongation are 1098.3 MPa and 12%, respectively.

Low-cost two-dimensional digital image correlation system

A low-cost digital image correlation (DIC) system for measuring two-dimensional displacement fields is described. Using an off-the-shelf camera, lens, and open-source DIC analysis software, displacement fields in aluminum and steel dog-bone tensile specimens were measured. Correction for out-of-plane motion is used to obtain strains from the displacement fields. Proposed DIC strain measurement system is validated using conventional thin-film strain gauges for strains below 1%. Average strain measurements from the DIC system were found to be within 1% of the measurement obtained using strain gauges. For strains between 1% and 10%, strain histories from the DIC systems displayed excellent correlation with strain measurements obtained using an extensometer.

Unidirectional fibre reinforcement of syntactic metal foams

Abstract Metal matrix syntactic foams are porous structures where the porosity is formed by introducing a porous filler material into the metal matrix. They have low density and absorb significant energy during compression but cannot withstand tensile stress. The main goal of this study was to apply unidirectional fibre reinforcement to syntactic metal foams. Therefore, a lightweight double-composite structure that can be utilised against tensile load and has advantageous properties during compression was created. Copper-nickel coated carbon fibre bundles were used as unidirectional long fibre reinforcement, lightweight expanded clay aggregate particles as filler material and Al99.5 aluminium as matrix material. The samples were created with vacuum infiltration and formed into cylindrical tensile specimens. Quasi-static tensile tests were carried out on the specimens and fibre trusses, and quasi-static compression was applied on specimens in the parallel and perpendicular direction to the unidirectional fibre truss.

A six degrees of freedom femtosecond laser system for fabrication of small-scale mechanical property specimens.

We present the details of a novel ultra-short pulsed laser machining workstation that has been employed for high-throughput laser machining of small-scale mechanical property specimens. This system employs a six degrees of freedom hexapod positioning stage capable of macroscopic movements at high positional accuracy. We developed a methodology that uses quantitative image analysis to measure key parameters required to minimize the hexapod positioning and rotational error. Application of this system to laser machining of small-scale 316L stainless steel tensile specimens and ultra-high molecular weight polyethylene compressive specimens using eucentric tilt and rotation about the specimen axis will be shown, where serial laser milling at a specimen tilt angle of 10° was used to effectively eliminate any taper in the sample cross section that is typically found in laser machining.

Residual mechanical properties of corroded ultra-high-strength steels and weld metals

This paper presents an in-depth investigation into the residual mechanical properties of ultra-high-strength steels and weld metals after exposure to corrosive environment. The tensile specimens of weld metals were fabricated using ER100S-G, ER110S-G, ER120S-G feedstock wires by robotic gas metal arc welding, whilst ultra-high-strength steel tensile coupon specimens were machined from the Q890 and Q960 steel plates. The high-strength steel and weld metal tensile specimens were exposed to neutral salt spray accelerated corrosion conditions. Six exposure durations were designed to achieve different corrosion degrees of specimens. A total of 23 corroded ultra-high-strength steel tensile coupon specimens and 19 corroded high-strength weld metal specimens were included. The geometric profiles of corroded steel specimens were determined via non-contact 3D laser scanning. Monotonic tensile tests were conducted to determine the stress-strain responses and key mechanical properties of corroded steel and weld specimens. Mechanical properties deterioration of corroded ultra-high-strength steels and weld metals are reported and discussed. Prediction equations on the residual mechanical properties regarding the tensile loading capacity, yield stress and ultimate tensile stress of ultra-high-strength steels and weld metals after exposure to corrosive environment were established.

Developing hybrid C-sections from waste and recycled composite materials

This paper investigates the performance of hybrid composites made from mixed waste plastics (wMP), recycled carbon fibre (rCF), and waste glass fibre (wGF). Two lay-up configurations with varying wGF and rCF contents were considered: one with approximately 7 vol% rCF (25 vol% wGF) and another with approximately 15 vol% rCF (9.4 vol% wGF). The tensile, compressive, and flexural performance of standard coupon specimens for both configurations were assessed, revealing that specimens with increased rCF content exhibited superior performance. Additionally, three hybrid C-sections, containing 15 vol% rCF, were thermoformed and subjected to axial compression. All three C-sections failed due to bearing failure, accompanied by some interlaminar delamination and material crushing at the loading ends. Their weight-specific load capacity surpassed that of similar sections published in the literature, such as ultra-thin-walled steel C-sections, by almost 95 %. A finite element model (FEM) of the C-section was developed and was able to predict reasonably well the stress versus strain response. These findings demonstrate that waste and recycled composite materials could serve as sustainable alternatives to ultra-thin-walled steel C-sections and other conventional materials commonly used in construction.

Tensile testing of S690QL1 HSS welded joint heterogeneous zones using small scale specimens and indentation methods

Abstract The welded joints are structures with significant heterogeneity, indicated by their fundamental segmentation into base metal (BM), heat affected zone (HAZ), and weld metal (WM). The heat affected zone, having width in millimeter scale for fusion welding processes, is further segmented into several characteristic regions, having differences in grain structure and size. The microstructural heterogeneity results in significant differences in mechanical properties of individual welded joint zones. Mechanical testing of such small material volumes is inconvenient, or even impossible, using the standard size specimens proposed in testing standards. Requirement to precisely position the specimens, even ones with subsize dimensions, and investigate mechanical properties of specific narrow HAZ regions presents certain challenge. This work investigates the X welded joint of S690QL1 grade high strength steel (HSS), welded with slightly overmatching filler metal. The material tensile properties are tested, using small scale specimens and indentation methods. Small scale specimens are ASTM E8 round tensile subsize and flat sheet mini tensile specimens (MTS). The indentation methods include hardness testing and profilometry-based indentation plastometry (PIP) method, to gain additional insights into material stress–strain behavior. Finally, paper evaluates the testing methods, comparatively processes the collected experimental data, and provides guidelines for heterogeneous structures testing.

Time-dependent behaviour of 3D printed fibre-reinforced limestone calcined clay cement concrete under sustained loadings

The evolution of 3D-printed concrete (3DPC) structures has made remarkable impacts in the construction industry and academia for prospective engineering practice globally. This is due to promising outcomes of various investigations on its construction coupled with several advantages it offers over conventional cast concrete. However, the time-dependent deformation of 3DPC under sustained loading is still unknown and requires extensive research. Quasi-static studies have also shown that creep could be of great concern due to its production technique involving layer stacking, which eventually leads to weak interlayer bond strength. This paper experimentally investigates the time-dependent behaviour of fibre-reinforced printed concrete (FRPC) containing limestone calcined clay cement (LC3) under sustained tensile and flexural loadings. The experimental tests conducted on LC3-FRPC specimens in two orthogonal directions were individual creep and shrinkage to determine other parameters associated with creep responses, including creep fracture. The specimens for tensile and flexural creep were subjected to sustained stresses of 40, 60 and 80 % of the tensile and 40 % flexural strength results obtained from quasi-static tests. The quantified creep is compared in terms of the difference in stress levels, as the results revealed that none of the specimens fractured under sustained loadings. Instead, higher direct tensile strengths were recorded for the creep specimens after 225 days loaded at different stress levels. Then, it is postulated that direct tensile tests on similar LC3-FRPC specimens without creep loading may confirm that the monotonic stress-strain response at the age at which the tests are terminated forms an envelope for creep fracture.

Influence of surface pre-deformation on the Portevin-Le Chatelier effect and the related multiscale complexity of plastic flow in an Al-Mg alloy

The influence of the surface pre-deformation on jerky flow caused by the Portevin-Le Chatelier (PLC) effect was investigated using flat tensile specimens of an Al-Mg alloy. Although jerky flow represents a macroscopic plastic instability, the underlying mechanisms stem from self-organization of dislocations, which pertains to deformation processes at mesoscopic scales. To provide a comprehensive approach, the investigation was carried out by coupling tensile tests, digital image correlation and acoustic emission techniques, each targeting a particular range of scales. Thin superficial layers were pre-deformed using surface mechanical attrition technique (SMAT). It was found that the observed effects depend on which surfaces are processed. Overall, the treated samples exhibited an enhanced yield strength without deterioration of ductility in comparison with the initial material. These changes in the general mechanical behavior are likely to be correlated with the changes in jerky flow. Using digital image correlation, a tendency to delocalization of bursts of plastic flow was found for both the PLC bands and smaller-scale strain heterogeneities outside the bands, the latter having been little studied so far. Unexpectedly, SMAT occurred to modify plastic flow drastically at this scale. In addition to clarification of the role played by the surface in the PLC effect, these findings provide new insights into relationships between deformation processes at distinct scales.

Hydrogen embrittlement of Zircaloy-4 fabricated by ultrasonic additive manufacturing

Ultrasonic additive manufacturing (UAM) was successfully applied to the zirconium material system to create a planar geometry. Following fabrication, SS-J3 type tensile specimens of the UAM and wrought Zircaloy-4 with a nominal gage section of 5 × 1.2 × 0.75 mm were machined for hydriding studies and mechanical testing. The SS-J3 type tensile specimens were gas-charged with hydrogen using a custom system that precisely controls hydrogen gas flow rate, hydrogen partial pressure, and temperature. To avoid altering the UAM material, the maximum process temperature was limited to 550 °C. Using different initial hydrogen gas pressures and flow rates, various hydrogen contents (70–1755 wppm) were achieved for Zircaloy-4 specimens. Tensile testing shows that, regardless of hydrogen content, all UAM specimens measured yield strengths in the range of 557 ± 16 MPa and ultimate tensile strengths of 660 ± 4 MPa. However, total elongation clearly decreased as a function of increasing hydrogen content. At the lowest hydrogen content, the total plastic elongation measured 21.5 %, and this value decreased to less than 2 % when the hydrogen content was increased to 1000 wppm. Cross-sectional optical microscopy images revealed that the hydride distributions are randomly oriented. For the low hydrogen content specimen, these randomly distributed hydrides are isolated from each other. A sandwiched structure, consisting of high-density and low-density layers, was also observed for the specimens with hydrogen content between 200 and 400 wppm. As the hydrogen content increases, the hydrides diffuse into the low-density hydride layers to form a network across the whole specimen. Although the tensile properties of UAM and wrought Zircaloy-4 exhibit the same behavior with increasing hydrogen content, the distinctions in grain orientations led to differences in the hydride orientations at low and intermediate hydrogen concentrations.

A Relationship between Fracture Toughness Kc and Energy Release Rate Gc According to Fracture Morphology Analysis

This study investigated the relationship between fracture toughness (Kc) and energy release rate (Gc) through fracture morphology analysis, emphasizing the critical role of fractal dimensions in accurately characterizing fracture surfaces. Traditional linear elastic fracture mechanics (LEFM) models relate Gc to Kc by combining energy principles with the nominal area of the fracture surface. However, real materials often exhibit plasticity, and their fracture surfaces are not regular planes. To address these issues, this research applied fractal theory and introduced the concept of ubiquitiform surface area to refine the calculation of fracture surfaces, leading to more accurate estimates of Gc and Kc. The method was validated through standard compact tensile specimen tests on a nickel-based superalloy at 550 °C. Additionally, the analysis of fractal dimension differences and dispersion in various fracture regions provides a novel perspective for evaluating the fracture toughness of materials.