Differences In Tensile Properties Research Articles

Tensile mechanical properties and damage analysis of layered woven GFRP composite bolts

Composite bolts have become one of the research focuses in screw threads joints due to their lightweight, high-strength, and wave transmission properties. We elucidate the differences in tensile properties, damage processes, and tensile failure forms between two types of layered woven GFRP composite bolts through tests and numerical simulations. It was found that the tensile strength of layered plain woven bolts is 40% higher than layered twill woven bolts. The failure forms of both types of bolts are related to their layered woven structure. The fracture surface of plain bolts is planar, while the fracture surface of twill bolts is apex shaped. Subsequently, a refined thread stretching model was established to study the effect of loading speed on the tensile property of screw threads. It was found that the tensile strength of plain woven screw threads and twill woven screw threads at a loading speed of 1 mm/min was 11% and 6% higher than that at 3 mm/min, respectively. The results show that the bolts and screw threads with layered plain woven have stronger tensile strength than those with layered twill woven, and a decrease in loading speed within a certain range can improve the tensile strength of the screw threads.

Reinforcing melt electrowritten elements with entangled multifibrillar strands for thin hydrogels with potential in bone resurfacing

Osteonecrosis of the femoral head (ONFH) is a disease that affects young adults in their thirties to fifties, representing the progressive destruction of the hip bone caused by deficient vascularization. As the condition slowly leads to complete collapse of the femoral head, the conventional solution is total hip arthroplasty. Thin scaffolds consisting of fiber-reinforced hydrogels could be used to regenerate the affected bone surface, coupled with hip resurfacing for less invasive approaches. Melt electrowriting (MEW) was used to produce polycaprolactone (PCL) reinforcing elements for thin scaffolds, with four mesh densities and highly tunable mechanical properties. The influence of the MEW process parameters on the PCL filaments’ morphology was investigated using Design of Experiments to optimize their fabrication and obtain tailorable structures with entangled fiber morphology for increased contact surface with the hydrogel component. Uniaxial tensile tests were performed to investigate the difference in tensile properties of the entangled design versus the aligned counterparts, including the exploration of the mesh size effect. The microstructure and microstructural changes of the entangled meshes at uniaxial tensile deformation were explored using micro-computed tomography. Plasma treated meshes were embedded in gelatin methacryloyl/alginate hydrogels, developing reinforced composite scaffolds with potential for bone surface reconstruction.

2 GPa H13 steels fabricated by laser powder bed fusion and tempering: Microstructure, tensile property and strengthening mechanism

The successful manufacture of crack-free and highly dense H13 tool steel using laser powder bed fusion (LPBF) has been widely reported. Although the phases contain only martensite and some (<20 %) of residual austenite (RA), the differences in tensile properties are very large in previous studies. Here, the microstructure and tensile properties of the LPBF-fabricated H13 steels with different heat treatments were comparatively studied. Tensile strengths ranged ∼2.0–2.2 GPa for the optimal as-built and direct-tempered samples. By increasing the heat input, the RA content was reduced to 0.1 % and the microstructure contained only hierarchically fine martensite with improved tensile properties and anisotropy. Based on the full-martensitic microstructure in the optimal as-built samples, secondary hardening was achieved by direct tempering at 530–590 °C with tensile strengths of ∼2.1–2.2 GPa and improved elongations (4.93–6.43 %). The optimal direct-tempered samples yielded higher tensile strengths compared to the standard heat-treated counterparts. For the direct-tempered samples, the substantial retaining of the fine martensitic structure and high density of dislocations introduced by LPBF was the key to the excellent properties rather than the precipitates. This work elucidated the effect of the LPBF process, direct tempering, and standard heat treatment on the tensile property of H13 steel. It is concluded that process optimization for LPBF fabrication of H13 steel requires not only defect avoidance but also fine martensite and low-content RA. On this base, the LPBF-prepared H13 steel can be directly tempered to further obtain components with excellent tensile properties, which are superior to the standard heat-treated counterparts.

Effects of Intercritical Heat Treatment on the Temper Embrittlement of SA508 Gr.4N Ni-Cr-Mo High Strength Low Alloy Steels for Reactor Pressure Vessels

To analyze the effects of intercritical heat treatment on the temper embrittlement of SA508 Gr.4N steels, two model alloys with different phosphorus (P) contents were fabricated. Each sample was heat treated by applying a conventional heat treatment process (quenching-tempering) with/without an intercritical heat treatment process (IHT) and a step-cooling heat treatment for temper embrittlement. Then their microstructure and mechanical properties were evaluated. The microstructure of the SA508 Gr.4N model alloy was composed of tempered lower bainite and martensite, and nano-sized precipitates formed both inside and at boundaries. The grain size was reduced when IHT was applied. There was a small difference in tensile properties according to the heat-treatment conditions and P contents, but the difference in Charpy impact properties was large. The heat treatment for temper embrittlement (TE) increased the impact transition temperature, and a very significant increase was observed in steels with a high P content. The increase in transition temperature owing to TE was reduced when IHT was applied. The fractograph analysis of Charpy fractured specimens at transition temperatures showed that an increase in intergranular fracture was main reason for the TE, and that IHT reduced the formation of intergranular fracture. The AES results showed that P-Ni was segregated at grain boundaries, and the level of segregation was reduced by applying IHT. This occurred because the formation of prior austenite grain boundaries by IHT dispersed the P at grain boundaries, and reduced the amount of P segregation.

Tensile behavior of UHPFRC made by a fiber orientation device with adjustable vibrational frequency

Ultra-High-Performance Fiber Reinforced Concrete (UHPFRC) not only has high compressive and tensile strength, but also exhibits strain-hardening characteristics in tension due to the addition of steel fibers. In this study, a new-style fiber orientation device equipped with a vibration motor of adjustable vibrational frequency was used to prepare UHPFRC. The wall effect and fiber length were considered in the manufacturing process of the device. Uniaxial tensile tests were conducted on fiber-oriented UHPFRC to explore the effects of vibrational frequency and corresponding vibrational force on the tensile behaviors. The test results showed that the elastic ultimate tensile strength, elastic ultimate tensile strain, tensile strength, peak tensile strain, and tensile elastic modulus of UHPFRC specimens cast by fiber orientation process at various vibrational frequencies were different. The fiber orientation parameters were quantitatively evaluated by the image analysis technique to explain the differences in tensile properties of the specimens. The effect of different vibrational frequencies on the tensile strength of UHPFRC matrix and its porosity was also considered. Therefore, this study provides a reference for how to adjust the vibrational frequency of the vibrating platform under the directional channel when pouring relevant components.

Precipitates evolution during isothermal aging and its effect on tensile properties for an AFA alloy containing W and B elements

A 20Cr-25Ni-2.5Al alumina-forming austenitic alloy containing W and B elements was aged at 923 K for 5000 h, and the microstructure and tensile properties with different aging time were investigated. NiAl, σ and Laves were observed at grain boundaries (GBs) successively. The matrix was covered by NiAl and Laves with the extension of aging. The evolution of precipitates during aging contributed to the variation of tensile properties. Precipitation of nanosized NbC carbides within grains and σ phase at GBs led to a rapid increase in strength and a decrease in elongation for 500 h aging sample. In the later stage of aging, the coarsening of NiAl and Laves phases, as well as the reduction in dislocation density caused a decline in strength. The coarsening of precipitates upon aging time follows the Ostwald ripening theory. Due to its lower diffusion rate in austenite compared to Mo, W may accelerate the growth of Laves at GBs. Boron was mainly enriched in Laves instead of NiAl, NbC and σ phases after high temperature aging. The addition of W and B improved the precipitation strengthening of Laves, increasing the high temperature tensile strength after long term thermal aging. The difference in tensile properties between room temperature and 923 K is due to the ductile–brittle transition of NiAl. No σ phase was observed within grains even after 5000 h aging and elemental chromium particles occurred around Laves due to boron hindering the growth of σ.

Research on anisotropy of the 7B50 super thick plate

In this study, the microstructure and in-plane anisotropy (IPA) of mechanical properties along the normal direction (ND) of the 7B50 Al super thick plate are mainly studied. When adopting the same heat treatment for the experiment, higher degree of recrystallization is displayed on the surface of the plate and lower degree is achieved in the center along the ND. The main textures developed through the plate are Brass, Cube, Copper and R textures. The maximum texture density along the ND occurs at the center and there exists a complex stress condition, resulting in the texture weakening at 10 mm ∼ 20 mm depth from the rolling surface. Considering the final mechanical properties, the IPA is not substantial along the ND compared with thin plates in other studies and the differences in tensile properties are mainly embodied in the nonuniform elongation. The main reason for this phenomenon may be attributed to the fact that growth and aggregation of micropores along the transverse direction (TD) are easier.

Crop Nitrogen Fertilization Schedule in Bread Wheat Affects the Mechanical Performances of Thermoplastic Films Obtained by Plasticization of Flours

Recent research has investigated the plasticization of wheat flour as a non-food alternative application. In this work, we analyzed the performances of thermoplastic films obtained using flours of two bread wheat cultivars (Bologna and Bora) grown in fall–spring under four nitrogen (N) fertilization treatments: (1) continuously well-N-fed (N300 = 300 kg N ha−1, split throughout the growth cycle); (2) N-fed only very early (N60-0 = 60 kg N ha−1, just one month after sowing); (3) N-fed only extremely late (N0-120 = 120 kg N ha−1 at pollination); (4) unfertilized control (N0). Flours were characterized for glutenin and gliadin fractions, Chopin’s alveograph parameters, Field Emission Scanning Electron Microscopy (FESEM) images, and thermogravimetric analysis (TGA), while films were evaluated for mechanical properties (tensile strength at break, σb; elongation at break, εb; Young’s modulus, E) and FESEM images. Differences among treatments for absolute and relative abundances of gluten fractions and alveographic parameters were extremely marked and gave rise to differences in tensile properties of thermoplastic films. Within each cultivar, the ranking of treatments for εb values was N0 &gt; N60-0 &gt; N0-120 &gt; N300. Thus, εb was inversely correlated with crop N availability and total gluten content of the flour. The σb was less variable among N treatments; however, in both cultivars, it was high in N0 and N300 and appreciably lower in N0-120. Overall, the best mechanical performances were obtained with flours from crops not subjected to imbalances in N nutrition (N0, N300). Our work demonstrates that bioplastic engineering needs to take into consideration the variability of biological source material like that caused by different crop N availability.

Effect of Part Thickness and Build Angle on the Microstructure, Surface Roughness, and Mechanical Properties of Additively Manufactured IN-939

Powder bed fusion-laser beam of metals (PBF-LB/M) has attracted significant interest due to the possibility of producing dedicated design features like thin-walled structures, even though their mechanical response and microstructure are not well understood. Hence, thin-walled IN-939 structures of different thicknesses (0.5, 1 and 2 mm) were manufactured at two build angles (90 and 45 deg) by PBF-LB/M. A preferred 〈100〉 crystallographic orientation was found along the build direction in all cases. The crystallographic texture intensity and surface roughness increased as the part thickness decreased for 90 deg and increased for 45 deg build angle. Reduction in wall thickness resulted in a decrease in the tensile properties, e.g., YS decreases by up to 33 pct and UTS decreases by up to 30 pct in comparison with the bulk specimen which had YS of 1051 ± 11 MPa and UTS of 1482 ± 9 MPa. Obtained results indicate that the apparent difference in tensile properties is primarily due to the overestimation of the load-bearing area. Two methods to estimate the accurate tensile properties based on roughness compensation are presented, using of which the corrected tensile performance of the thin-walled specimens was comparable with a standard tensile specimen.

X-ray computed tomography analysis of pore deformation in IN718 made with directed energy deposition via in-situ tensile testing

Directed energy deposition (DED) is a metal additive manufacturing technique often used for larger-scale components and part repair. It can result in material performance that differs from conventionally processed metal. This work studies spatial and orientation-based differences in tensile properties of nickel-based alloy IN718 using in-situ x-ray computed tomography to observe internal pore populations. Anisotropy and spatial variability in mechanical properties are shown while the evolution of pore shape during deformation is measured. Measured pore deformation is compared to predict deformations simulated using a computational crystal plasticity scheme, which provides insight, through inverse modeling, to the grain orientation in which the pore resides. The measurements provide a high fidelity method to compare experimental and computational approaches to pore deformation studies. Pore deformation measurements show that pores tend to grow and elongate in the direction of loading, consistent with ductile deformation and likely deforming with the material. Generally, the pore defects observed in this material (not from lack-of-fusion) do not cause so-called premature failure, and fully developed necking occurs prior to fracture.

Tensile properties of TIG welded 2219-T8 aluminum alloy joints in consideration of residual stress releasing and specimen size

Different dimensions of tensile test specimen can be used for qualification of welding procedure according to the existing standard. However, they are found to be dissimilar in tensile properties. In this study, the tensile properties of TIG welded 2219-T8 aluminum alloy joints were tested with different tensile specimen sizes. The welding residual stress releasing, specimen size effect, as well as fracture criteria were taken into account by using a sequential “welding - cutting - tensile” finite element simulating method. Results indicated that the degree of welding residual stress releasing decreased with the increasing of specimen width. For specimens with 250 mm width, over 80% of the residual stresses were kept. Tensile testing result showed that the tensile strength and elongation of joint decreased when the specimen width increased. The differences in tensile properties were proved to result from the size distinctions, rather than residual stress releasing, because the stress triaxialities were different in the specimens with different sizes. This phenomenon was precisely simulated by using the Johnson–Cook fracture criterion. Eventually, the constitutive equations of Johnson–Cook model were established based on the experimental tensile strengths to describe the tensile behaviors of 2219 aluminum alloy joints.

Mechanical testing and microstructural analysis of wire arc additively manufactured steels

Wire arc additive manufacturing (WAAM) is a metal 3D printing method that allows the cost-effective and efficient production of large-scale elements, and has thus gained great interest from architects and structural engineers. Integration of this novel technology into the construction industry, however, requires the development of a clear understanding of the mechanical behaviour of WAAM materials. To this end, a comprehensive experimental study into the mechanical properties and microstructure of WAAM plates made of normal- and high-strength steels has been undertaken and is reported herein. A total of 137 as-built and machined tensile coupons were tested, extracted in various directions relative to the print layer orientation from WAAM plates of two nominal thicknesses, built using different deposition strategies. The influence of the geometric undulations inherent to the WAAM process and deposition strategy on the resulting mechanical properties was investigated. Microstructural characterisation was also performed by means of optical microscopy (OM) and electron backscatter diffraction (EBSD). The WAAM normal-strength steel plates exhibited a principally ferritic-pearlitic microstructure, while the WAAM high-strength steel plates displayed a mixed microstructure featuring ferrite, bainite and martensite. The EBSD analysis revealed a weak crystallographic texture, which explained the observed mechanical properties being almost isotropic. No significant differences in tensile properties were observed with the different deposition strategies, except for some variation in ductility. The geometric undulations of the as-built coupons resulted in some reduction in effective mechanical properties and a degree of anisotropy. Overall, the examined WAAM material exhibited consistent mechanical properties, a Young’s modulus comparable to conventionally-produced steel plates, marginally lower strength, reflecting the slower cooling conditions than is customary, and good ductility.

An investigation on tensile and fatigue properties of cast Al-7Si-1.5Cu alloy applied in cylinder head considering size effect phenomenon

The cylinder head is one of the most critical diesel engine components. Under service conditions, different loads are exerted on the cylinder head, leading to the failure of various degrees at different positions of the cylinder head. In this study, the differences in mechanical properties at the different positions of the cylinder head are investigated by sampling specimens, metallography measurement, tensile and fatigue tests, and fracture surface analysis. Meanwhile, the Weibull statistical distribution method is used to analyze the size effect of the specimen. The results show that the microstructure features of the cylinder head exhibit high spatial heterogeneity. The mechanical properties are affected by microstructure features. The tensile properties of the top plate are optimum, followed by the flame plate, and the connecting wall has the worst properties. The difference in tensile properties at different positions is mainly affected by the grain and eutectic structure. In the same position, the tensile and fatigue properties of standard specimens are better than small specimens. The porosity is the critical parameter determining the tensile and fatigue properties of the different specimens. In addition, based on the statistical analysis of mechanical properties, the relationship of mechanical properties between the standard and small specimens was established. Through the established relationship, the mechanical properties of small specimens can be used to predict the mechanical properties of standard specimens, and the predicted value is in good agreement with the experimental data.

Mechanical and Microstructural Anisotropy of Laser Powder Bed Fusion 316L Stainless Steel.

This paper aims at an in-depth and comprehensive analysis of mechanical and microstructural properties of AISI 316L austenitic stainless steel (W. Nr. 1.4404, CL20ES) produced by laser powder bed fusion (LPBF) additive manufacturing (AM) technology. The experiment in its first part includes an extensive study of the anisotropy of mechanical and microstructural properties in relation to the built orientation and the direction of loading, which showed significant differences in tensile properties among samples. The second part of the experiment is devoted to the influence of the process parameter focus level (FL) on mechanical properties, where a 48% increase in notched toughness was recorded when the level of laser focus was identical to the level of melting. The FL parameter is not normally considered a process parameter; however, it can be intentionally changed in the service settings of the machine or by incorrect machine repair and maintenance. Evaluation of mechanical and microstructural properties was performed using the tensile test, Charpy impact test, Brinell hardness measurement, microhardness matrix measurement, porosity analysis, scanning electron microscopy (SEM), and optical microscopy. Across the whole spectrum of samples, performed analysis confirmed the high quality of LPBF additive manufactured material, which can be compared with conventionally produced material. A very low level of porosity in the range of 0.036 to 0.103% was found. Microstructural investigation of solution annealed (1070 °C) tensile test samples showed an outstanding tendency to recrystallization, grain polygonization, annealing twins formation, and even distribution of carbides in solid solution.

Organosolv Lignin Barrier Paper Coatings from Waste Biomass Resources.

The aim of the study was to isolate lignin from organosolv, beech tree (Fagus sylvatica), and Japanese knotweed (Reynoutria japonica), to use it for paper surface and to replace part of the non-renewable product resources with bio-based ones. A total of nine coated samples with different lignin formulations and starch were compounded, prepared, and evaluated. The basic (grammage, thickness, specific density), mechanical (elongation at break, tensile, burst and tear indices), and barrier properties (contact angle, water penetration, water vapour permeability, kit test) of the coated papers were investigated. The analysis showed no significant difference in tensile properties between uncoated and coated samples. Furthermore, the decrease in water vapour transmission rate and the lower contact angle for coated samples were nevertheless confirmed. The novel coating materials show promising products with very good barrier properties. Finally, the correlation between structural, morphological, and (other) natural lignin-based factors was revealed, highlighting the importance of parameters such as the equivalence ratio of aliphatic and phenolic hydroxyl groups or the average molecular weight. Tuning functionality by design could optimise performance in the future.

Experimental Study on a Microwave Composite Forming Process Based on a SiC Mold for Manufacturing Fiber Metal Laminate.

The microwave composite forming (MCF) process can reduce manufacturing cost because the process time is reduced by the dielectric heating of the mold and the composite material. In a previous study, the MCF process using a commercial microwave oven with a polytetrafluoroethylene mold was applied. Disadvantages of the previous MCF process have been investigated. These included the difference in tensile properties according to the cutting location, absence of a method to measure temperature during the MCF process, and the fact that the input power cannot be controlled according to the temperature. To solve these problems, a microwave oven with a silicon carbide mold was proposed in this study. Uniaxial tensile tests were conducted to obtain the tensile properties of the fiber metal laminate (FML) specimen. In addition, a microscopic image was captured to investigate the non-adhesive area. The tensile properties and thickness distribution of the FML specimens manufactured by the proposed and previous MCF processes were compared according to the cutting location of the FML sheets. Furthermore, the non-adhesive area was quantified to compare the processes. The results revealed that the proposed MCF process improved the tensile properties of the FML specimen and reduced the non-adhesive area.

Influence of fused filament fabrication parameters on tensile properties of polylactide/layered silicate nanocomposite using response surface methodology

AbstractThis study aimed at assessing and optimizing the influence of printing speed and extrusion temperature in a fused filament fabrication (FFF) process on the tensile properties of a polylactide/layered silicate nanocomposite. Mathematical models using Doehlert designs were formulated to examine factor and interaction effects. The models were corroborated by measurements using capillary rheology, tomographic images, and crystallinity analyses to find physical explanations for the differences in tensile properties. The tensile properties were a non‐monotonic function of printing speed, which may be due to various deposition defects that influence the porosity of composite tensile specimens. This study provides new insights into FFF process optimization regarding rheological behavior and mesostructure of nanocomposite by highlighting new modes of deposition defects that originate from process parameter settings and materials. The results contribute to the properties mastery of FFF‐processed materials.

Synergetic strengthening of additively manufactured (CoCrFeMnNi)99C1 high-entropy alloy by heterogeneous anisotropic microstructure

In this study, the heterogeneous anisotropic microstructure and mechanical properties of additively manufactured (CoCrFeMnNi)99C1 high-entropy alloy (HEA) are comprehensively investigated using experimental and theoretical analyses. For the present alloys, the selective laser melting (SLM) process produced orthogonally anisotropic microstructure with not only strong macroscopic morphological but also sharp microscopic crystallographic textures. Moreover, due to the complex thermal gradient and history in the melt pools, the columnar grains were heterogeneously evolved along the building direction with alternatively arranged layers of fine and coarse grains parallel to the laser scanning direction. This unique morphological texture played a dominant factor for the big difference in tensile properties between different loading directions in the early stage of deformation. In particular, the alternatively arrangement of fine and coarse grains could generate high hetero-deformation induced (HDI) hardening along the scanning direction in the as-built samples by profuse evolution of geometrically necessary dislocation at the boundaries of each layer. On the other hand, upon the last stage of plastic deformation, the crystallographic texture played a crucial role in directional flow behavior by modulating twinning activity. The combined contribution of the various anisotropic microstructural factors to the tensile properties of the SLM-processed HEAs was clarified both qualitatively and quantitatively. This work will shed light on effective utilization of both heterogeneity and anisotropy of the structural parts for customized performance via expanding multi-scale freedom of design in additive manufacturing.

Process Development: Burr and Film Formation during High Speed Punching of Extruded PC Based Polymers

First investigations focus on the usage, processing and material properties of polycarbonate (PC) based materials used in cable duct production. Test coupons were taken from in-situ cable ducts including further additives generally used in industry. Different mechanical and optical analytical methods were performed. Significant differences in tensile properties of polycarbonate/ acrylonitrile butadiene styrene (PC/ABS) compared to mineral reinforced PC were observed. The hardness of mineral reinforced PC is significantly dependent on the geometry of the cable ducts. The fracture behavior and morphology of the PC/ABS fracture surface is directly related to the coupon temperature during Charpy impact testing. The process temperature influences the failure behavior during high impact processing such as high speed punching. Due to the lower impact strength of mineral reinforced PC less film and burr formation compared to PC/ABS are likely. However, the mineral distribution is not homogeneous and therefore subject to further investigation. This study aims at a better understanding of process properties of PC/ABS products, parameter selection, quality improvement and general understanding of underlying microstructural and surface properties.

Surface modification of polyvinyl alcohol (PVA)/polyacrylamide (PAAm) hydrogels with polydopamine and REDV for improved applicability.

Developing a small-diameter vascular graft with a satisfactory performance in terms of mechanical and biological properties remains a challenging issue because of comprehensive requirements from clinical applications. Polyvinyl alcohol (PVA)/polyacrylamide (PAAm) hydrogels exhibit many desirable characteristics for small-diameter vascular grafts because of their tunable mechanical properties, especially high compliance. However, poor cells adhesion hinders their application for endothelialization in situ. Therefore, in the present work, polydopamine (PDA) and tetrapeptide Arg-Glu-Asp-Val (REDV) were used to functionalize the hydrogels surface and improve cells adhesion. A series of characterizations were systematically conducted to examine the applicability of coated hydrogels to small-diameter vascular grafts. Results showed that bare and coated hydrogels have appropriate structural stability, and no significant differences in tensile properties could be found after being coated with PDA or PDA-REDV. The hydrophilicity of the hydrogels decreased with the coatings of PDA and especially PDA-REDV to improve protein adsorption, porcine iliac artery endothelial cells (PIECs) adhesion, viability, proliferation, and spreading on the hydrogels. Lower hemolysis percentages and higher blood clotting index values were attained for the hydrogels, suggesting their satisfactory hemocompatibility. Overall, the present work provided insights into the development of a novel hydrogel-based small-diameter vascular graft. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 108B:117-127, 2020.