Tensile Tests Research Articles

On the feasibility of a predictive model of mechanical properties of AM Inconel 718 thin wallets produced by DED-LB process monitored with thermal methods

AbstractNickel-based superalloys are widely used in applications requiring resistance to high temperatures and high strain rates. Various additive manufacturing (AM) processes, such as Laser Metal Deposition (LMD), a Directed Energy Deposition (DED) process, can be used to produce these components. The quality of the components depends on the process parameters, so it is crucial to investigate the influence of each parameter and their combinations through extensive experimental campaigns. In this scenario, it would be very important to predict the mechanical properties of the produced components through the online monitoring of the process parameters using non-destructive techniques, such as thermography. The aim of this work was to explore the feasibility to predict the mechanical properties of Inconel 718 thin wallets around 10 mm produced by DED-LB, based on the extraction of suitable thermal features directly during the production. An experimental campaign analysed the effect of different process parameters (laser power, scan speed, powder flow rate, and energy density) on the mechanical properties achieved. All sample production was monitored with an infrared uncooled camera integrated with the laser head moving at the same scan speed. After the process, hardness measurements and tensile tests in both growth directions were carried out for each sample to evaluate the mechanical behaviour of the "as-built" coupons and the influence of selected process parameters. Macrographic analyses of the material structure were performed to determine the morphology of the passes and the degree of overlap between different passes and layers. Various thermal features and statistical models were considered to demonstrate the possibility of establishing a predictive model. The obtained results demonstrated the correlation between the hardness and the apparent temperature assuming a confidence level of 95%, and the possibility of predicting in this sense the final macrostructure and the mechanical behaviour of the printed material considering an empirical model with the R2 coefficient around 0.8.

Effects of nanosilica and nanocellulose on poly(butylene adipate‐co‐terephthalate) nanocomposites for food packaging applications

AbstractPolymeric materials are highlighted in the global market due to their low cost, excellent properties, and diversity of applications, such as food packaging, which in addition to protecting packaged foods also promotes control and conservation against contaminants. Thus, the objective of this research is to investigate the effects of adding silica nanoparticles and cellulose nanofibers, alone and together, on the properties of poly(butylene adipate‐co‐terephthalate), aiming for application in food packaging. For this purpose, PBAT and the nanofillers were initially mixed in a rheometer to produce masterbatches, and, then, to be processed by a single screw extruder to generate the nanocomposites. The nanocomposites are analyzed by scanning electron microscopy, x‐ray diffraction, thermogravimetric analysis, differential scanning calorimetry, nuclear magnetic resonance, tensile testing, water contact angle, and microbial permeability. In low concentrations, it is observed that the system tends to be less heterogeneous. Nanoparticles do not interfere with thermal stability and present a barrier to microorganisms. Interestingly, in the two conditions studied, polymers with cellulose nanofibers or silica nanoparticles have filtering capacity, being effective as physical barriers to the growth of microorganisms within 60 days. However, the effect on mechanical properties is small, being more pronounced with the use of cellulose nanofibers.

Stress relaxation aging of 7050 aluminum alloy under elastic and plastic loadings: A perspective from the geometrically necessary dislocations

Aerospace integral panels with large curvature often experience not only elastic loading but also plastic loading during creep age forming. However, the stress relaxation aging behaviors and mechanisms under loading stresses ranging from elastic to plastic regions, especially from the perspective of geometrically necessary dislocations (GNDs), have not been fully explored. The stress relaxation aging (SRA) behavior of 7050 aluminum alloy under elastic (200/250/300 MPa) and plastic loadings (350/400 MPa) are studied by uniaxial SRA, hardness and tensile tests, and corresponding mechanisms are clarified by Electron Back Scatter Diffraction (EBSD) tests and transmission electron microscopy (TEM) observations. Regardless of the loading stress, the stress relaxation of 7050 alloy shows a typical two-stage behavior (rapid stress reduction and stable stress relaxation rate). The second stage of stress relaxation under elastic loading shows an abnormal stress rebound, while the stress continuously decreases under plastic loading, and hardness and yield strength at 350 MPa are lower than that at 200 MPa during SRA. These results are attributed to strong dislocation pinning from small and dense precipitates at elastic loading and dislocations shearing large and sparse precipitates at plastic loading, respectively. Furthermore, both the stress reduction and its ratio increase with the increase of initial stress. GNDs contribute to the formation of low-angle grain boundaries (LAGBs) and accumulate at the LAGBs intersection to coordinate grain orientation for creep deformation. Compared to elastic loading, plastic loading promotes global growth of intragranular precipitates by elastic stress field and local heterogeneous nucleation and coarsening of precipitates at subgrain boundaries by more GNDs.

Improving the performance of polyvinyl chloride with added natural extracts for medical storage

Abstract Polyvinyl chloride (PVC) is a candidate biopolymer for medical packaging due to its inertness to biological fluids, high 
mechanical and chemical resistance, and wide range of processing possibilities. Blood bags were fabricated to obtain a 
flexible blood bag with high durability, antibacterial resistance, and good bio-properties. Recently, most of the problems 
related to blood bags available in hospitals are related to the synthetic plasticizer added to the base material to provide the 
required flexibility for application, but these synthetic materials harm human blood as they lead to blood dissolution and thus 
blood corruption quickly. So the present work focuses on modifying the properties of PVC by incorporating extracted natural 
materials including basil seeds at different concentrations (1%, 2%, and 3%) using solvent cast method. Then, extracted 
wheat gel at concentrations (0.5 and 1%) was added to composite samples containing basil seed gel (3%). The resulting 
samples were characterized by tensile, water absorption, FTIR, wettability, transparency, antibacterial, and hemolytic tests. It 
was found that the ultimate tensile strength decreased with increasing concentration of two additives. While the elastic 
modulus value decreased when basil seed gel was added, but tended to increase when wheat gel was added. The elongation 
ratio results showed improvement with the addition of gel. The results showed that the water absorption and wettability of the 
composites increased with the increase of the additive concentration. The results also showed that these materials had better
resistance to S. aureus and C. albicans bacteria. The transparency and hemolysis results decreased with the addition of a gel 
enhancer. According to the obtained results the resultant composite has better properties than commercial blood bags and is 
more suitable for blood bags.

Stability of kangaroo rat burrows in the Sonoran Desert: Evidence of biocementation

Kangaroo rats (Dipodomys deserti) construct complex burrow systems in loose desert sand that survive temperature and relative humidity fluctuations and storms. Animals that burrow in desert sand typically burrow in compacted sand, near plant roots, or when the soil is unsaturated. However, these processes are insufficient to explain tunnel stability of kangaroo rats. Our goal is to understand how kangaroo rat burrows remain stable in loose desert sand, intending to translate this knowledge to geotechnical engineering. A kangaroo rat habitat in the dunes of The Sonoran Desert, AZ, was selected for the study. Dynamic cone penetrometer tests performed at active, abandoned, and no-burrow sites demonstrated that the animals prefer loose sand for burrow construction. Soil samples collected from the burrows' ceilings, subsurface, and surface were characterized. Brazilian tensile strength test results showed that burrow soil has approximately 3 times greater tensile strength than the rest at dry state, which indicates increased interparticle attractive stress in burrow ceilings due to biocementation. Laboratory experiments, scanning electron microscopy, and confocal microscopy images showed that fungal and microbial biofilms provided 17 kPa increase in interparticle attractive stress at less than 1% biomass concentration, indicating potential to be used in soil improvement applications.

Indentation-Free Resistance Spot Welding of SUS301L Stainless Steel

Paint-free bodywork has become an attractive alternative for rail vehicles, in the direction of easy maintainability and low manufacturing costs. However, conventional resistance spot welding inevitably leaves indentation marks to detrimentally reduce the optical homogeneity of the paint-free bodywork. In light of this, indentation-free resistance spot welding is proposed for joining SUS301L stainless steel sheets in order to achieve superior surficial integrity. A tiny SUS301L steel ball with a diameter of 1.5 mm was chosen as the intermediate filler between two steel sheets to avoid the formation of surficial indentation. The influence of welding current and welding time on the mechanical properties of joints was studied. The optimal parameters of the mechanical properties were obtained when the welding current was 8.0 kA, the welding time was 150 ms, the electrode pressure was 0.35 MPa, and the electrodes were cylindrical planar electrodes, which was determined by comparing the tensile shear test results. The surficial indentation depth was less than 1% of the plate thickness, and no observable indentations were seen on the surface of the optimized welding spots.

Novel method to assess anisotropy in formability using DIC

In this study, a novel technique was developed to identify localized neck of a tensile sample based on the curvature of the surface that is expected to work with any metal in which a localized neck forms prior to fracture. Moreover, a MATLAB-based computational tool has been developed to conduct advanced mathematical computations and numerical analysis on data generated from uniaxial tensile test of DP980 steel coupled with Digital Image Correlation (DIC) based on the novel curvature method. The presented curvature technique is a geometry-based approach that uses the specimen's surface profile and groove geometry to detect localized necking, avoiding the limitations of strain-based methods in distinguishing between localized and diffuse necking. A detailed analysis was conducted on the accuracy of the onset and anisotropy of localized neck. The results of the study revealed that specimens fabricated with 30-degree orientation with respect to the Rolling Direction (RD) of the sheet metal, exhibit a higher level of total strain at the onset of the localized necking, indicating the influence of anisotropy on the material's behavior for DP980. Moreover, consistent R-values were observed among specimens with the same orientation with respect to the RD, exhibiting a rising trend of R-value for orientations from zero to 60-degree, followed by a decrease from 60 to 90-degree. Furthermore, the results exhibited a negative linear relationship between R-values and the magnitude of thinning strain.

On the Competition between Pores and Hidden Entrainment Damage during In Situ Tensile Testing of Cast Aluminum Alloy Components

The competition between pores and hidden entrainment defects during tensile testing of specimens from Al-Si-Cu alloy high-pressure die castings has been characterized. In all tests, multiple strain concentrations have been identified by using the digital image correlation technique and the final fracture has been preceded by a competition between pores and hidden damage, later identified as oxide bifilms. The results have confirmed previous findings that overall damage to the metal during its liquid state is much more extensive than what can be assessed via X-ray inspection, which looks only for pores. It is concluded that current quality assurance techniques need to be updated.

Examination of the Effects of Chemical Treatments on the Mechanical, Chemical, and Physical Characteristics of <i>Hibiscus rosa-sinensis</i> Plant Fiber

Natural fibres in recent years have been found to contribute a great share in making composites. Hibiscus rosa-sinensis plant fibres which are natural were used in this work and have not yet been tried to make the composites so far and easily available thus making this study very necessary it aims to perform various chemical treatments and to study the physical and chemical properties of them. The methodology adopted was that literature review, problem identification, extraction of fibres, treatment of fibres, chemical and mechanical testing of fibres, results and discussions and conclusion. Fibre chemical composition tests were also done to determine the constituents of the fibres. Two chemical treatment methods (alkalinization and benzoylation) were proposed in this work. Chemical treatments were found to improve surface roughness. Using Scanning Electron Microscopy (SEM), researchers examined the fibres' structural and morphological alterations and discovered that components like pectin were largely eliminated. The structural properties of fibres were known from X-ray diffractograms, and crystallinity percentages were found for the cellulosic fibres. Fourier Transform Infrared (FTIR) spectroscopy presented the spectra of the fibres which revealed the structure of organic compounds and the presence or the absence of functional groups. It showed the partial removal of hemicellulose and lignin. Axial tensile tests were performed for the fibres to know the maximum tensile force and percentage elongation. Chemical treatments partially removed impurities in the fibres and made morphological changes. The improvements in mean tensile values and percentage elongation were found in 5% alkali-treated and benzoylation-treated fibres, 56% and 63% higher than the untreated fibres respectively.

Comparison of FE Simulation and Experiment on Tensile Test of TWB-HPF 22MnB5 Steel

Finite element (FE) analysis of the tensile test of TWB-HPF 22MnB5 steel was performed and compared with the experimental results. To improve the accuracy of the simulation, the damage theory of FLD and ductile damage theory were used in 2D and 3D simulations. The tensile strength of 22MnB5 steel was determined under various welding heat inputs for FE simulation. Crack propagation of the welded region indicated that the fracture was observed in the base metal under normal welding conditions. Also, the crack propagated along the HAZ region due to higher heat input of the welding, and lead fractures have been highlighted as a potential complication.

Effect of Star-like Polymer on Mechanical Properties of Novel Basalt Fibre-Reinforced Composite with Bio-Based Matrix.

This study is aimed at developing a fibre-reinforced polymer composite with a high bio-based content and to investigate its mechanical properties. A novel basalt fibre-reinforced polymer (BFRP) composite with bio-based matrix modified with different contents of star-like n-butyl methacrylate (n-BMA) block glycidyl methacrylate (GMA) copolymer has been developed. n-BMA blocks have flexible butyl units, while the epoxide group of GMA makes it miscible with the epoxy resin and is involved in the crosslinking network. The effect of the star-like polymer on the rheological behaviour of the epoxy was studied. The viscosity of the epoxy increased with increase in star-like polymer content. Tensile tests showed no noteworthy influence of star-like polymer on tensile properties. The addition of 0.5 wt.% star-like polymer increased the glass transition temperature by 8.2 °C. Mode-I interlaminar fracture toughness and low-velocity impact tests were performed on star-like polymer-modified BFRP laminates, where interfacial adhesion and impact energy capabilities were observed. Interlaminar fracture toughness improved by 45% and energy absorption capability increased threefold for BFRP laminates modified with 1 wt.% of star-like polymer when compared to unmodified BFRP laminates. This improvement could be attributed to the increase in ductility of the matrix on the addition of the star-like polymer, increasing resistance to impact and damage. Furthermore, scanning electron microscopy confirmed that with increase in star-like polymer content, the interfacial adhesion between the matrix and fibres improves.

Characterize the high-temperature steady-state rheological behavior and Arrhenius activation of PEEK via strain rate jump tensile tests

Polyetheretherketone (PEEK) is a high-performance thermoplastic polymer with diverse industrial applications, such as aerospace, automotive, electronics, and medical devices. However, systematic research on its high-temperature rheological characteristics is inadequate. In this study, strain rate jump tensile tests were introduced to examine the steady-state rheology phenomena and strain rate sensitivity of PEEK at four different temperatures and nine different strain rates. Theoretical analysis based on the free volume theory and the Arrhenius law was also carried out to further analyze the transition of PEEK from Newtonian flow to non-Newtonian flow. Results indicate that PEEK materials exhibit a transition from Newtonian flow to non-Newtonian flow similar to metal materials at high temperatures. The transition point from Newtonian flow to non-Newtonian flow is marked by the emergence of steady-state rheology and its characteristic stress. Theoretical analysis demonstrates that the transition of PEEK is in accordance with the Arrhenius low. Moreover, its apparent activation energy (1.42 eV) is significantly lower than that of metal materials (5.28 eV), indicating a lower energy barrier and an easier transition. The strain rate sensitivity index correlates negatively with rising temperatures, especially at lower rates. This study enhances understanding of PEEK's rheological characteristics at high temperatures, aiding the development and application of high-performance thermoplastic materials.

A trust region algorithm for finite-strain plasticity with strongly coupled hardening

As extensions to our Lagrangian finite-strain plasticity framework based on the approximate exponential integrator, we introduce two new algorithms: (i) a fixed-radius trust region root finder for the nonlinear system involving the elastic right Cauchy Green tensor and plastic multiplier (ii) a partitioned approach for the hardening variables, which are determined in a staggered form using the strongly-coupled concept typically adopted for multiphysics problems. This allows the use of intricate hyperelastic laws combined with recent yield functions, which otherwise would involve a laborious treatment, and the use of corresponding work-hardening. Work-hardening would introduce significant nonlinearities in the constitutive system if used in a fully-coupled form. For the partitioned approach, a dynamic relaxation algorithm is adopted. This allows the efficient solution of the two nonlinear equations without significant drifting. Results show that robustness and efficiency are significantly improved. Herein, algorithms are described in detail. Significant testing is performed with imposed strains up to 100 for a carbon steel. This contributes to the robustness of equilibrium iterations. Drifting is also assessed as a function of number of steps in the dynamic relaxation algorithm. Numerical experimentation is performed in the 3D tension test for an anisotropic yield function.

Research on the connection performance and micro-hydration mechanism of super-performance grouting material for prefabricated component connections

Abstract The performance of grouting material determines the connection reliability of prefabricated components and the overall safety of the structure. In order to realize the rapid connection of prefabricated components, improve the construction efficiency and improve the quality of component connection. The research group has developed a grouting material with fast early strength improvement and high late strength. The formation mechanism was analyzed by scanning electron microscopy. The reliability of grouting material was verified by uniaxial tensile test of sleeve grouting connector. The results show that : CH, AFt and C-S-H are formed inside the grouting material, and the cementing system is dense inside. The skeleton formed by AFt inhibits the shrinkage of the system, which can provide support for the later compressive and flexural strength. Uniaxial tensile test results and theoretical analysis. The external reinforcement of the sleeve is broken, and the bonding performance between the grouting material and the reinforcement inside the sleeve is reliable. The internal bond stress is far less than the failure stress of the connector, which is about 50 % of the failure stress.

Microstructural evolution and mechanical properties of Al-4Ni-0.4V alloyed with Zr and Ti at elevated temperatures

The influence of Zr and Ti alloying on the microstructural evolution and mechanical properties of an Al-4Ni-0.4V alloy at elevated temperatures was investigated. The results showed that the coarsening rate of the eutectic Al3Ni phase in the Al-4Ni-0.4V-0.2Zr-0.2Ti alloy decreased from 21.1 nm3/s in the Al-4Ni-0.4V alloy to 7.4 nm3/s after annealing at 350 °C for 0 h to 120 h. The tensile strength, yield strength, and elongation at room temperature of the annealed Al-4Ni-0.4V-0.2Zr-0.2Ti alloy (350 °C, 8 h) were 181 MPa, 108 MPa, and 27.2 %, respectively. After tensile test at 350 °C, these values of the annealed Al-4Ni-0.4V-0.2Zr-0.2Ti alloy were 108 MPa, 72 MPa, and 29.8 %, respectively. Transmission electron microscopy results revealed the precipitation of the L12 ordered structure of the Al3M (M = Zr, V, Ti) phase, approximately 2 nm in size, in the α-Al after annealing. These phases exhibited excellent lattice matching with the α-Al and considerable precipitation strengthening. Segregation of Zr, V, and Ti elements at the α-Al/Al3Ni interface hindered Ni diffusion in the matrix, thereby reducing Al3Ni phase coarsening. Moreover, the Al3M phase precipitated at the interface exhibited favorable matching with the lattice planes of the α-Al and Al3Ni phase, which improved the thermal stability of the eutectic structure and the mechanical properties at elevated temperatures.

Evaluation of U-Notch and V-Notch Geometries on the Mechanical Behavior of PVDF: The DIC Technique and FEA Approach.

The notch effect of semicrystalline PVDF was investigated using U- and V-notch geometries with different depths, and tensile tests were performed at 23 °C using the DIC technique and FEA. Both unnotched and notched dumbbell-shaped specimens were subjected to tensile loading with the DIC technique to obtain mechanical curves and strain maps. The experimental data were compared to a numerical model, analyzing both global mechanical curves and local strain maps around the notch region to assess the accuracy of the simulations. The results demonstrated that the geometry and depth of the notch influence the mechanical behavior of PVDF, presenting a decrease in load and displacement compared to unnotched specimens. This aspect was corroborated by strain maps, which showed the increase in the local strain around the notch tip. For FEA, the global analysis indicated a good correlation with experimental results, and the local analysis demonstrated a reasonable agreement in strain map results within 0.5 mm of the notch neighborhood. Overall, the DIC technique and FEA provided a reliable evaluation of notch behavior on the PVDF used as pressure sheaths with reasonable precision.

Impact of Ultrasonic Welding Parameters on Weldability and Sustainability of Solid Copper Wires with and without Varnish.

This article contains an advanced analysis of the properties of solid wire electrical contacts produced by ultrasonic welding, both with and without varnish. The main disadvantage of ultrasonic welding of thin wires is the inability to achieve acceptable peel force and tensile strength, which is mainly due to the deformation and thinning of the wires. This study deals with ultrasonic welding using a ring of thin solid copper wires that minimises the deformation and thinning of the wires. The influence of welding parameters such as energy, pressure and amplitude were systematically analysed. Based on these parameters, the optimum welding programme and control method was determined to weld unvarnished and varnished wires. The investigations included electrical resistance tests, optical microscopy, micro-hardness measurements, peel tests and tensile tests, and the measurement of energy consumption. The results showed no significant differences in microstructure and hardness between varnished and unvarnished joints. Ultrasonic joints of varnished wires achieved lower electrical conductivity (by 38%), lower tensile strength (by 3%) and higher peel strength (by 7%), while the welding process was more sustainable in terms of energy (by 6.6%) and time consumption (without preprocessing).

Dissimilar fabrication of the TC4/Ni60 bimetallic structure by laser melting deposition using a V/Cu transition bilayer

The bonding of Ti and Ni alloys to manufacture high-quality bimetallic structures represents an optimal integration strategy for fully leveraging their superior performance. However, the metallurgical bonding between TC4 and Ni60 dissimilar metals is extremely challenging due to the formation of TiNi, TiC and TiFe brittle intermetallic compounds and the differences in thermophysical properties. To address this issue, this paper presents a solution based on the compatibility of elemental components. A V/Cu transition bilayer was designed to achieve defect-free bonding between TC4 and Ni60 by laser melting deposition. The microstructure of the TC4/Ni60 bimetallic structure was analyzed by SEM, XRD and EBSD to evaluate its feasibility. The results indicate that the generation of brittle intermetallic compound phases was reduced to a certain extent when a V/Cu transition bilayer was employed, thus preventing cracking and peeling of the TC4 substrate and Ni60 cladding layer. Additionally, the mechanical properties of the bimetallic structure were evaluated through micro-shear tests and tensile tests. The micro-shear test results indicate that the weakest layer of the bimetallic structure is the Cu transition layer with a shear strength of 183.0 ± 108.8 MPa and an indentation rate of 8.25 ± 3.3 %. The room temperature tensile results demonstrate that the developed bimetallic structure fractured at the Cu/Ni60 interface, exhibiting a tensile strength of 286.3 ± 54.1 MPa and an elongation of 6.3 ± 0.5 %. The expected research can provide valuable references for improving the mechanical properties of TiNi dissimilar bimetallic structures produced by laser melting deposition.

Development of zeolite 5A-incorporated polyvinyl alcohol membrane for desalination by pervaporation

Abstract With the rapid depletion of potable and useable water resources globally due to population growth and the effects of global warming, the desalination of seawater – the world’s largest source of water – to acceptable quality levels is critical to meeting future water needs. This study investigates the use of zeolite 5A-incorporated polyvinyl alcohol membranes to produce fresh water from seawater for industrial and domestic use and evaluates the application of the pervaporation process on the separation performance. Polyvinyl alcohol and polyvinyl alcohol/zeolite 5A mixed matrix membranes were prepared by solution-casting technique, and their morphological, structural, and mechanical properties were analyzed by field emission scanning electron microscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy, and tensile strength tests. The swelling behavior and pervaporation performance of the membranes were investigated at different temperatures (30, 45, and 60 °C) using synthetic seawater containing 35 g L−1 NaCl, and membrane–solvent interactions were determined using data from sorption experiments. The membrane produced water flux and salt rejection values at 60 °C of 5.82 kg m−2 h−1 and >99.9 %, respectively.

The SCC behavior of MAO/EPD biocomposite coatings on Ti-6Al-4V alloy

Aseptic loosening and inadequate osseointegration are significant issues associated with titanium alloy implants in complex body fluid environments. Surface coatings techniques are often employed to enhance the bioactivity and osseointegration capabilities. In this research, biocomposite coatings were fabricated on Ti-6Al-4V alloy employing micro-arc oxidation (MAO) and the integration of micro-arc oxidation/electrophoretic deposition (MAO/EPD) technology. Microstructure, bioactivity, and corrosion resistance of the coatings were studied. To investigate the effect of the coatings on the stress corrosion cracking (SCC) behavior of Ti-6Al-4V alloy, slow strain rate tension (SSRT) tests were conducted in simulated body fluid (SBF). Results show that the adhesive strength of the MAO/EPD composite coatings is around 28.41N, with an average contact angle of 19.05 °, indicating excellent wettability and biocompatibility. The corrosion rate of biocomposite coatings is 3.43 μm·a−1 and the biocomposite coatings exhibit excellent SCC resistance, with a SCC sensitivity of 9.21%, which is significantly lower than the 18.39% of Ti-6Al-4V alloy. This can be attributed to the lower porosity of the coatings, which can provide excellent protection for the alloy.