Tensile Bars Research Articles

The Influence of the Ratio of Circumference to Cross-Sectional Area of Tensile Bars on the Fatigue Life of Additive Manufactured AISI 316L Steel

The static and dynamic loading capacities of components depend on the stress level to which the material is exposed. The fatigue behavior of materials manufactured using additive technology is accompanied by a pronounced scatter between the number of cycles at the same stress level, which is significantly greater than the scatter from a material with the same chemical composition, e.g., AISI 316L, but produced by rolling or forging. An important reason lies in the fact that fatigue cracks are initiated almost always below the material surface of the loaded specimen. Thus, in the article, assuming that a crack will always initiate below the surface, we analyzed the fatigue behavior of specimens with the same bearing cross section but with a different number of bearing rods. With a larger number of rods, the circumference around the supporting part of the rods was 1.73 times larger. Thus, experimental fatigue of specimens with different sizes showed that the dynamic loading capacity of components with a smaller number of bars is significantly greater and can be monitored by individual stress levels. Although there are no significant differences in loading capacity under static and low-cycle loading of materials manufactured with additive technologies, in high-cycle fatigue it has been shown that the ratio between the circumference and the loading cross section of tensile-loaded rods plays an important role in the lifetime. This finding is important for setting a strategy for manufacturing components with additive technologies. It shows that a better dynamic loading capacity can be obtained with a larger loading cross section.

Dynamic tensile behaviors and crack propagation in fiber-reinforced cementitious composites: Experimental investigation and Peridynamic simulation

Fiber-Reinforced Cementitious Composites (FRCC) have gained significant attention in engineering applications due to their superior mechanical properties and toughness, particularly under high strain rate conditions. This study performed dynamic tensile tests on FRCC at high strain rates (35-110 s⁻¹) using a Split Hopkinson Tensile Bar (SHTB) apparatus. Additionally, a novel Peridynamic (PD) model was developed for the SHTB and FRCC system, leveraging the advanced capabilities of the emerging PD theory. The study compared and analyzed dynamic tensile strength, ultimate tensile strain, strain rate effects, failure modes, and crack development in FRCC with different fiber ratios at various high strain rates, using both experimental data and PD simulations. The results show that the PD-SHTB-FRCC dynamic model developed in this study exhibits high consistency between numerical simulations and experimental findings, effectively capturing the processes of crack initiation, propagation, and complete failure in FRCC specimens. The dynamic tensile properties of FRCC improve significantly with increased strain rates, with polyethylene (PE) fibers providing superior reinforcement compared to steel fibers. Notably, the dynamic tensile strength, peak tensile stress, and ultimate tensile strain of FRCC increase significantly with rising strain rates, with specimens containing higher PE fiber content showing a more pronounced enhancement effect. For strain rates between 42.6 s⁻¹ and 76.1 s⁻¹, considering dynamic tensile strength, ultimate tensile strain, and peak tensile stress, the optimal combination for resisting dynamic tensile loads was 1.5% PE fibers and 0.5% steel fibers. At a strain rate of 99.8 s⁻¹, a 2% PE fiber ratio alone provided the best performance.

Plastic strain effect on cleavage microcracks propagation in probabalistic statement. Part 2. Research results

The second part of the paper presents the results of uniaxial tension testing of smooth round bars of 2Cr–Ni–Mo–V steel in the thermally-embrittled state and St3 steel in the initial state. SEM examination of the fracture surfaces is carried out. The brittle fracture probability is calculated using the Prometey model presented in the first part of this article. It has been found that the plastic strain effect on the microcrack propagation probability is caused by two reasons: (1) the critical brittle fracture stress increase due to formation of new barriers for microcrack under plastic deformation, and (2) the working volume decrease due to the neck formation in tensile round bar. A unified set of parameters has been proposed to take into account the plastic strain effect on cleavage microcracks propagation probability for WWER-1000 RPV steel and low-alloyed low-strength steel.

Evaluation of Post-Processing on Additive Manufactured Bioresorbable Polymers for Medical Devices.

Additive manufacturing (AM) has seen massive growth in the medical device sector and an increase in the clearance of devices. Many challenges still exist in the design, development, and clinical use of AM-fabricated devices, notably the processing, annealing, and sterilization of resorbable polymers. In addition, the use of these materials continues to grow in medical devices and scaffold technologies for tissue engineering and regenerative medicine (TERM). Specifically, this study focused on the scaffold mechanical properties post-processing and throughout a simulated resorption (in vitro) study. Herein, we evaluated three (3) materials that span a range of mechanical properties and degradation rates relating to a range of tissue healing rates and mechanical properties affording the opportunity of biomimetic potentials, Caproprene 100M, Lactoflex 7415, and Lactoprene 100M. These bioresorbable polymers were additively manufactured into scaffold forms of Type V tensile bars to investigate post-processing parameters. A range of heat treatments were then performed after the AM process to induce a range of semicrystalline morphologies, and subsequently, two different sterilization techniques were performed, one based on super critical carbon dioxide and another using electron beam radiation. It was statistically shown that the heat treatment parameters and the sterilization method had statistically significant effects on the scaffold properties of each material. While material differences were responsible for the majority of the mechanical property breadth, techniques utilizing analysis of variance allowed the observation of significant effects and interactions associated with heat treatment, sterilization, and material parameters (alpha = 0.05). The characterization of the sample groups provided insight into the process-structure-property-performance relationships of the resorbable scaffold samples. It was established that the post-processing impacted the scaffold structures, and therefore, sterilization and heat treatment selections should be included within initial design considerations alongside material selection as critical for device development, especially when AM bioresorbable scaffolds for TERM.

Radiation and thermal embrittlement of RPV steels: the links of embrittlement mechanisms, fracture modes and microcrack nucleation and propagation. Part 2. Strength and plasticity properties

The uniaxial tension test results are represented over wide temperature range for smooth round bars of 2Cr–Ni–Mo–V steel and A533 steel used for RPVs of WWER and PWR types. These steels are studied in the following states: (1) the initial (as-produced) state; (2) the thermally embrittled state modelling hardening mechanism of embrittlement; (3) the thermally embrittled state modelling non-hardening mechanism of embrittlement; (4) the irradiated state. The true stress-strain curves are determined over wide temperature range that is required for calculation of the stress-and-strain fields for various specimens. The true stress-strain curves for the investigated steels in the initial and thermally embrittled states are obtained when using standard mechanical characteristics. For the irradiated steels the true stress-strain curves are obtained when using the data of the digital video recording under continuous in-testing monitoring of the cylindrical parts of tensile bars. For the irradiated materials the procedure based on standard characteristics cannot be used as it is connected with very small strain. The procedure based on the digital video recording data is verified by comparison of the stress-strain curves obtained for the initial and thermally embrittled states on the basis of the digital video recording data and standard characteristics.

Impact of Runner Size, Gate Size, Polymer Viscosity, and Molding Process on Filling Imbalance in Geometrically Balanced Multi-Cavity Injection Molding.

The injection molding process is one of the most widely used methods for polymer processing in mass production. Three critical factors in this process include the type of polymer, injection molding machines, and processing molds. Polypropylene (PP) is a widely used semi-crystalline polymer due to its favorable flow characteristics, including a high melt flow index and the absence of a need for a mold temperature controller. Additionally, PP exhibits good elongation and toughness, making it suitable for applications such as box hinges. However, its tensile strength is a limitation; thus, glass fiber is added to enhance this property. It is important to note that the incorporation of glass fiber increases the viscosity of PP. Multi-cavity molds are commonly employed to achieve cost-effective and efficient mass production. The filling challenges associated with geometrically balanced layouts are well documented in the literature. These issues arise due to the varying shear rates of the melt in the runner. High shear rate melts lead to high melt temperatures, which decrease melt viscosity and facilitate easier flow. Consequently, this results in an imbalanced filling phenomenon. This study examines the impact of runner size, gate size, polymer viscosity, and molding process on the filling imbalanced problem in multi-cavity injection molds. Tensile bar injection molding was performed using conventional injection molding (CIM) and microcellular injection molding (MIM) techniques. The tensile properties of the imbalanced multi-cavity molds were analyzed. Flow length within the cavity served as an indicator of the filling imbalance. Additionally, computer simulations were conducted to assess the shear rate's effect on the runner's melt temperature. The results indicated that small runner and gate sizes exacerbate the filling imbalance. Conversely, glass fiber-filled polymer composites also contribute to increased filling imbalance. However, foamed polymers can mitigate the filling imbalance phenomenon.

Contribution of spatially variable pitting corrosion on fatigue life prediction of RC beams

Pitting corrosion induces stress concentration in steel bars, significantly reducing the fatigue life of reinforced concrete (RC) beams. Moreover, spatially variable pitting corrosion can cause fatigue fractures in tensile steel bars at various cross-sections of beams, not just at the mid-span section. This will further increase the failure probability of beams but is rarely considered by existing studies. Thus, this study proposes a fatigue life prediction method for RC beams experiencing spatially variable pitting corrosion. First of all, the spatial variability of pitting corrosion in tensile steel bars in RC beams is simulated through the three-dimensional laser scanning method and the spectral representation method, in which the steel bar diameter, length, distance, corrosion level, and the correlation between corrosion pits are systematically considered. Subsequently, the fatigue crack initiation and propagation of pitting corroded steel bars are modeled based on fracture mechanics. The spatial analysis is then conducted on corroded RC beams until fatigue failure occurs. The proposed prediction method is verified with results from existing references. The findings highlight that neglecting the spatial variability of pitting corrosion leads to an overestimation of the fatigue life of corroded RC beams, especially under uniformly distributed loadings and high corrosion levels. This study provides a reasonable prediction for the lifespan of corroded RC beams.

Behavior of corroded HSC beams repaired by sprayed UHTCC and textile: Experimental study and theoretical analysis

Behaviors of twelve high strength concrete (HSC) beams were studied, including one control specimen, five corroded but non-repaired beams, and six corroded beams repaired by sprayed ultra-high toughness cementitious composites (UHTCC) with or without textile reinforcement. Galvanostatic accelerated corrosion technique was adopted, and three targeted corrosion levels (5 %, 10 %, and 15 %) were selected for each tensile steel bar. Corrosion-induced results, such as voltage change, crack initiation, concrete spalling, corrosion crack length and width, and non-uniform corrosion of steel bars were studied and compared with the results observed in normal strength concrete (NSC) beams. Structural behaviors, including failure modes and load-displacement responses were investigated through four-point bending tests. Results revealed that compared to NSC beams, HSC beams sustained more severe damages under a comparable corrosion level. Spalling was observed at a relatively lower corrosion ratio of 4.43 % and the maximum non-uniform corrosion coefficient, which was defined as the ratio of the maximum corrosion ratio to the average corrosion ratio, was 4.28. Corrosion-induced bonding degradation can alter the failure mode of corroded specimens in bending tests from bending to debonding. For repaired beams, however, the bonding degradation effect was reduced and bending failure was observed for all specimens. The bearing capacity of the beams repaired with sprayed UHTCC cannot be restored with a 12.42 % corrosion ratio, while the beams repaired with sprayed UHTCC/textile can recover their capacity even at a 13.6 % corrosion ratio. Furthermore, an improved theoretical model based on the fiber section analysis and virtual work method was developed to predict structural bending responses. The comparison of the experimental and theoretical results indicated the average corrosion ratio-based method may overestimate the loading capacity, especially for the beams with severe corrosion.

Evaluation of Different ZX Tensile Coupon Designs in Additive Manufacturing of Amorphous and Semi-Crystalline Polymer Composites

The layer-by-layer deposition of molten polymer filament in fused deposition modeling (FDM) has evolved as a disruptive technology for building complex parts. This technology has drawbacks such as the anisotropic property of the printed parts resulting in lower strength for parts printed in the vertical Z direction compared with the other two planes. In this manuscript, we attempt to address these challenges as well as the lack of standardization in sample preparation and mechanical testing of the printed parts. The paper focuses on process parameters and design optimization of the ZX build orientation. Type I tensile bars in ZX orientation were printed as per the ASTM D638 standard using two (2B) and four (4B) tensile bar designs. The proposed design reduces material loss and post-processing to extract the test coupons. Printing a type I tensile bar in the ZX orientation is more challenging than type IV and type V due to the increased length of the specimen and changes in additional heat buildup during layer-by-layer deposition. Three different polymer composite systems were studied: fast-crystallizing nanofiller-based high-temperature nylon (HTN), slow-crystallizing nanofiller-based polycyclohexylene diethylene terephthalate glycol-modified (PCTG), and amorphous carbon fiber-filled polyetherimide (PEI-CF). For all the polymer composite systems, the 2B showed the highest strength properties due to the shorter layer time aiding the diffusion in the interlayers. Further, rheological studies and SEM imaging were carried out to understand the influence of the two designs on fracture mechanics and interlayer bonding, providing valuable insights for the field of additive manufacturing and material science.

Effectiveness evaluation of different steel fibers on the shear strength of reinforced SFRC slender beams without web rebars

Current studies have mainly focused on the effect of specific steel fibers on the shear performance of steel fiber-reinforced concrete (SFRC) slender beams. However, there has been a lack of in-depth research evaluating the effectiveness of different steel fibers through a statistically comparative analysis of experimental data from various researchers. Existing design methods do not fully account for the impact of all types of steel fibers on the shear capacity of SFRC slender beams, providing very limited guidance on selecting appropriate steel fibers. This highlights the need for research to verify the strengthening effectiveness of different steel fibers. This paper establishes databases comprising 232 shear-failed reinforced SFRC beams with four other types of steel fibers straight wire, deformed wire, deformed cut-sheet and ingot mill, based on a comprehensive review of published literature. These databases complement an existing database of 280 reinforced SFRC beams using hook-end wire steel fibers as shear reinforcement. The databases are used to evaluate the validity of several well-known existing formulas for predicting the shear capacity of beams and to determine the fiber bond factor values that reflect the diverse strengthening effects of different steel fibers. Utilizing a simi-empirical synergetic prediction model for the shear strength of reinforced SFRC slender beams with hook-end wire steel fibers, the shear resistances of test beams in databases with the other four types of steel fiber are analyzed. The primary contributors to shear capacity are identified as the uncracked shear-compression SFRC and the dowel action of longitudinal tensile steel bars. The contribution of steel fibers is linked to the shear resistance of uncracked shear-compression SFRC. From a practical design perspective, a conservative prediction formula is verified, aligning with the lower boundary of the tested shear strength obtained from the database of beams. Finally, suitable steel fibers for s enhancing the shear strength of reinforced SFRC beams without web rebars are suggested based on their effectiveness.

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.

Flexural Behavior of Precast Rectangular Reinforced Concrete Beams with Intermediate Connection Filled with High-Performance Concrete

Precast rectangular reinforced concrete (PRRC) beams are joined on construction sites using concrete in situ to achieve the desired length. Limited research exists on the effect of intermediate connection shapes and the types of infilled concrete on the flexural performance of PRRC beams. This paper presents a comprehensive experimental and numerical investigation into the performance of PRRC beams with various intermediate connection geometries and infilled materials under flexural loading. The study examines rectangular, triangular, and semi-circular intermediate connections, along with the performance of beams infilled with normal concrete (NC), engineered cementitious composites (ECC), ultra-high-performance ECC (UHPECC), and rubberized ECC (RECC). The experimental results indicate that the rectangular intermediate connection exhibits superior performance in terms of strength and energy absorption compared to the triangular and semi-circular shapes. Beams incorporating UHPECC demonstrated the most significant improvements in strength and energy absorption, outperforming those with ECC and RECC for any shape of intermediate connection. Moreover, beams with rectangular connections and UHPECC infill exhibited the most significant increase in energy absorption and ultimate load compared to the beams with ECC and RECC. The ultimate load of the beams with UHPECC and tensile reinforcement bar diameters of 10 mm and 12 mm increased by 13% and 29%, respectively, compared to the control beam. The energy absorption of the beams with tensile reinforcement bar diameters of 10 and 12 mm was found to be 75% and 184% higher, respectively, than the control beam. In addition, an increase in tensile bar diameter was found to enhance both the energy absorption and the ultimate load capacity of the beams, regardless of the type of infill concrete. Beams incorporating UHPECC demonstrated the most significant improvements in strength and energy absorption, outperforming those with ECC and RECC. In particular, beams with rectangular connections and UHPECC infill exhibited an increase in energy absorption and ultimate load of up to 184% and 29%, respectively. UHPC was calculated to be as high as 184%, and 29%, respectively, compared to the control beams. In addition, an increase in tensile bar diameter was found to enhance both energy absorption and ultimate load capacity. Finite element modeling (FEM) was developed and validated against the experimental results to ensure accuracy. A parametric study was conducted to study the effects of various concrete types in triangular and semi-circular connections, as well as the influence of intermediate connection length on semi-circular connections under flexural loads. The findings reveal that increasing the length of intermediate connections increases the ultimate load of the beams.

Effect of geometric parameters on dynamic fracture toughness of compact tensile specimens

In this paper, the dynamic fracture toughness test and numerical simulation of CT specimens of 2A12-T4 aluminum alloy were carried out by using strain gauge method and finite element method based on Hopkinson tensile bar experiment device. The influence of crack transverse shape, loading hole size and dimension on the dynamic fracture performance of CT specimens was explained. The experimental and simulation results show that for CT specimens with different internal cracks, the time to reach stress equilibrium at the same tensile stress wave loading is roughly the same, while the time of initial cracking varies slightly. The dynamic fracture toughness obtained by concave arc-shaped internal crack and straight line-shaped internal crack is basically the same, while other changes in crack shape have a large impact. For CT specimens with straight line-shaped cracks, the position of the loading hole has a small effect on the dynamic fracture of the CT specimen under the same tensile stress wave. However, when the position of the loading hole is fixed, changing the diameter of the loading hole has a significant effect on the dynamic fracture toughness of the CT specimen.

Experimental investigation of Lord Kelvin’s isentropic thermoelastic cooling and heating expression for tensile bars in two engineering alloys

ABSTRACT Solids change temperature when rapidly and elastically stressed. The effect proposed by W. Thomson, who was ennobled as Lord Kelvin, is adiabatic thermoelastic cooling or heating depending on the sign of the stress. A highly sensitive radiometrically calibrated, cooled infrared camera was employed to measure temperatures both decreasing and increasing. Temperature measurements made from the reversible, elastic part of the stress–strain curve during rapid uniaxial tensile loading and unloading were investigated. The quasi-isentropic cooling temperature from the stress loading curve is recovered by heating after the specimen fractures when the load is released. These measurements establish for the first-time isentropic temperature recovery. The materials tested are an AISI 4340 steel and an aluminium 2024 alloy. Measurements of the stress cooling are − 0.65 ± 0.05 K/GPa for steel and − 1.8 ± 0.3 K/GPa for aluminium alloy. The thermoelastic heating is − 1.2 ± 0.3 K/GPa for steel and − 1.8 ± 0.2 K/GPa for aluminium. These values are compared to Thomson’s theoretical thermoelastic prediction; comparisons are also made to equations of state tables. The experimental values are below theoretical predictions. The quasi-isentropic, elastic part of the temperature change is fully recovered after extensive plastic deformation by the fracture stress release wave.

Investigation into microstructure, mechanical properties, and compressive failure of functionally graded porous cylinders fabricated by SLM

As the utilization of additively manufactured (AM) functionally graded porosity (FGP) structures continues to rise in various industries, there is a growing need for a comprehensive understanding of their design, microstructure, mechanical behavior, and failure mechanisms. This study involves the design and fabrication of FGP specimens with an 85 % volume fraction using selective laser melting (SLM) and 316L stainless steel powder, focusing on characterizing porosities, printing quality, and microstructure. Experimental tests, including tensile, quasi-static compression, and Split Hopkinson Pressure Bar tests, are conducted to assess the material behavior. Additionally, finite element analysis (FEA) and experimental compression tests are employed to investigate the compressive mechanical behavior and failure modes of FGP structures. The findings indicate that porosity distribution has minimal impact on the compressive behavior, specific energy absorption (SEA), and toughness of FGP structures. Furthermore, reducing the volume fraction from 85 % to 75 % in the S1FG samples increases the SEA by 7.2 % and changes the toughness by 5.9 %. Notably, porosity distribution influences fracture position and failure mechanisms during compression tests.

Finite Element Ductile Fracture Simulation of Charpy and Drop Weight Tear Tests for API X52

This paper presents a systematic procedure for performing finite element (FE) impact ductile fracture simulation of Charpy (CVN) and Drop Weight Tear Tests (DWTT) with validation using test data of API X52. For deformation and fracture models, the Johnson-Cook (J-C) model is used, of which seven parameters are determined by analyzing (1) round bar tensile test data at three different temperatures (two parameters), (2) tensile test and fracture toughness test at room temperature (three parameters) and (3) instrumented Charpy test (load–displacement) data at room temperature (two parameters). FE impact fracture simulation results with the determined parameters show good agreement with instrumented CVN test data at three different temperatures (0 °C, −30 °C and −60 °C) and DWTT data at temperatures of RT and −30 °C. For DWTT simulation, an analysis of the pre-strain due to flattening is included. Additionally, sensitivity analyses for the effect of adiabatic heating and strain rate on simulation results show that, although both phenomena should be considered in simulation, the strain rate effect is more significant than the adiabatic heating effect.

Sensitivity of mechanical properties to processing defects: Is tensile testing an appropriate metric for laser beam metal powder bed fusion machine qualification?

The Laser-based Powder Bed Fusion of Metals (PBF-LB/M) process has shown potential in the manufacturing of critical flight components, yet also has faced difficulties in achieving reproducibility. One potential reason for this is that tensile testing, which is one of the methods traditionally used to ascertain quality in the additive manufacturing (AM) industry, is insufficient for capturing underlying flaws in an additively manufactured component. To quantify the ability of tensile testing to detect underlying flaws in a component, a generalized full factorial experiment was performed where the tensile properties of UNS N07718 were measured across several types of build conditions. Combinations of differently sized bars and surface conditions were investigated. Defects were induced by amplifying the polygon delay parameter, hence prolonging the dwell time of the laser in the contours. The authors found that those tensile bars that experienced increased polygon delay had ∼10x more pores than those built with nominal parameter values while still maintaining an average porosity of <0.25 % (i.e., a total part porosity that is acceptable by NASA-STD-6030). Regardless of the specimen geometry and surface condition, differences between parts which had undergone polygon delay and those that had not were either statistically insignificant or were too small to be relevant, indicating that tensile testing may not be an effective metric for identifying the quality of a PBF-LB/M process.

AlCrTaTiZr-based high entropy alloy nitride coatings on stainless steel substrates: Characterization and microscale tension testing

High entropy alloy nitride coatings promise improved mechanical properties and are under current investigation for a range of applications. In this work, we report deposition of high entropy alloy nitride coatings on 316 stainless steel substrates by inductively coupled plasma assisted dc magnetron reactive sputtering of nominally equiatomic AlCrTaTiZr alloy targets. Characterization of coating composition and structure was carried out through X-ray photoelectron spectroscopy, Rutherford backscattering spectrometry, X-ray diffraction, and scanning/transmission electron microscopy. Mechanical testing was conducted through instrumented nanoindentation, interfacial shear loading through micropillar compression, and tension loading of coated microscale tensile bars in a scanning electron microscope. Microscale tension testing offers a potential avenue to assess the limiting shear strength of the coating/substrate interface, as well as the level of cohesion within the coating. The present study indicates that microscale tension tests yield results consistent with macroscale testing, while avoiding the need for multiple macroscale specimens. The present results suggest that cohesion of the high entropy alloy nitride coating and limiting shear strength of the coating/steel interface both increase with increasing substrate bias voltage during deposition, and that these coatings may be more adaptive to increased levels of ion bombardment during deposition without inducing excessive residual stresses.

Investigating mechanical properties and energy absorption of elastomeric polymer nanocomposites containing cellulose nanofibers in tensile, quasi-static compression, and high strain rate tests

In this study, mechanical properties and energy absorption of elastomeric nanocomposites reinforced with cellulose nanofibers are investigated from tensile, Quasi-static Compression (QSC), and Split-Hopkinson Pressure Bar (SHPB) tests. For this purpose, the design and preparation of rubber nanocomposites with different loadings of cellulose nanofibers (CNFs) were carried out, and the optimal cure temperature (T90) of the rubber compound containing cellulose nanofibers was determined from the rheometer test. In the continuation of this study, the effects of adding cellulose nanofibers on the tensile strength, elongation to break, and energy absorption of the proposed Nano-composites were investigated. The results showed that the nanocomposite containing 6 phr increases the ultimate strength and elastic modulus of 300% by 33.5% and 22.7%, respectively, compared to the control rubber (0 phr). Similarly, these numbers are about 10 and 65% for loading 12 phr cellulose nanofibers. From the results of the quasi-static compression test for different amounts of cellulose nanofibers at a strain rate of 50%, it was found that the lowest and highest compressive stress due to the resistance of elastomeric nanocomposites is related to the control sample (0 phr) and the 12 phr sample, respectively. Also, from high strain rate tests of Split Hopkinson Pressure Bar, it was found that the fracture mechanism of flexible composites containing cellulose nanofibers changes in response to a high-speed impact, and the samples respond to high-pressure impact with brittle fractures. It was also found that rubber nanocomposites reinforced with cellulose nanofibers are very sensitive to strain rates. As the strain rate increases, the energy absorption of rubber nanocomposites increases. The optimal loading (6 phr) of cellulose nanofibers in rubber compounds makes them suitable for energy absorption applications. Cellulosic nanofibers provide acceptable dispersion of nanomaterials through good interaction with natural rubber and lignin-carbon fillers. Therefore, through the physical interweaving of fillers with polymer chains, CNF provide better binding of polymer chains to improve properties.

Deformation and failure behavior of 2024-T42 sheet under impact loading

The deformation and failure behavior of 2024-T42 aluminum alloy sheet was investigated through a combined experimental-numerical method. Nine types of specimens were designed to cover a wide range of stress triaxialities and strain rates. Quasi-static and dynamic tests were carried out by electronic testing machine and split Hopkinson tensile bar respectively, and digital image correlation (DIC) method was introduced to measure the deformation. The phenomenological damage model GISSMO (generalized incremental stress state dependent damage model) and Johnson-Cook model were adopted to simulate all of the above tests and the load-displacement curves through numerical simulation were derived. An optimization method was developed to obtain all the model parameters by matching the load-displacement curves from simulation with those from tests by LS-OPT. Finally, drop weight tests and tensile tests of the central-hole plate were conducted. The applicability and accuracy of the damage models were verified by comparing the simulation results with the experiments, which indicates that GISSMO model predicts better the tests than the Johnson-Cook failure model.