Offset Yield Strength Research Articles

Development of novel ultrafine grain cu metal matrix composites reinforced with Ti-Cu-Co-M (M: Ni, Zr) amorphous-nanocrystalline powder

Novel ultrafine grain composites of Cu matrix reinforced with 2-50 wt. % of Ti48Cu39.5Ni10Co2.5 and Ti48Cu39.5Zr10Co2.5 (at. %) amorphous-nanocrystalline alloy particles have been fabricated by powder metallurgy. The composites showed a homogeneous structure. The characterization of composites was performed by optical and scanning electron microscopy (SEM), X-ray powder diffraction (XRD), micro- and macrohardness, as well as density measurements. After hot-pressing the crystallite size of Cu was smaller than 200 nm and nanocrystalline phases of reinforcing powder were 5-35 nm. Densities of 97-76 % relative to calculated values of consolidated composites were obtained, depending on the reinforcing weight fraction. Additionally, the mechanical properties and electrical resistivity of composites have been investigated. The results reveal that the 0.2% offset compressive yield strength of composites increases by two and five times, with respect to pure Cu matrix, for the composites reinforced with 2 and 50 wt. % of reinforcing particles, respectively. Electrical resistivity increases continuously, with higher values after 30 wt. % of addition. Changes in mechanical and electrical properties were produced by the increase of amorphous-nanocrystalline additive.

Anomalous High-Temperature Strengthening of an Al <sub>0.5</sub>CoCrCuFeNi Dual-Phase High-Entropy Alloy

Mechanical response of an Al0.5CoCrCuFeNi high-entropy alloy was investigated through uniaxial compression tests, the 0.2 % offset yield strength decreases with increasing temperature up to 773 K. However, at temperatures above 773 K, two anomalous yield strength hardening regions peaked at 873 K and 1073 K were observed. Microstructure analyses reveal an enhanced L12 ordering with the increase of compression temperatures and the subsequent precipitation of B2 phase at 973 K. Meanwhile, transmission electron microscopy observations of the deformation structure reveal that reveal that plastic deformation is carried primarily by dislocation at room temperature, but changes to deformation twinning at temperatures higher than 873 K. At temperature higher than 1073 K, a mix of dislocations and deformation twins is observed. These findings suggest that the yield strength anomaly is strongly related to the phase stability of high-entropy alloys at high deformation temperatures.

Microstructure and Mechanical Properties of ITER Correction Coil Case Material

The modified 316LN austenitic stainless steel was selected as ITER correction coils case material to provide structural reinforcement to the winding pack. Considering the case structure, high-assembling accuracy and other strict requirements, 316LN in special extruded form has been developed. In the present study, the microstructure and mechanical properties of the material were investigated. The microstructure of the 316LN material was analyzed by means of the optical microscopy, transmission electron microscope, and X-ray diffraction. It was observed that the material presents fine grain size and a single austenitic phase. Moreover, the intergranular corrosion resistance of the 316LN was evaluated and the results indicated that it exhibited a remarkable intergranular corrosion resistance. The tensile properties of materials were measured at both room and cryogenic temperatures. The 0.2% offset yield strength ( $R_{p0.2}$ ), ultimate tensile strength ( $R_{m}$ ), and elongation at break ( A ) at 4.2 K were determined to be higher than 800 MPa, 1500 MPa, and 40%, respectively. Furthermore, the J-integral fracture toughness of the 316LN was tested through means of an unloading compliance method at 4.2 K and the plane strain fracture toughness $K_{Ic}$ converted from the J-integral are well above the specified value of 180 MPa√m. In addition, the fatigue test and fatigue crack growth rate of the 316LN stainless steel were also investigated at 4.2 K. According to these results, all requirement of the case material including uniform microstructure, excellent corrosion resistance, and good mechanical properties established by the ITER IO are confirmed.

Experimental characterization of the mechanical properties of 3D-printed ABS and polycarbonate parts

PurposeThis paper aims to present the methodology and results of the experimental characterization of three-dimensional (3D) printed acrylonitrile butadiene styrene (ABS) and polycarbonate (PC) parts utilizing digital image correlation (DIC).Design/methodology/approachTensile and shear characterizations of ABS and PC 3D-printed parts were performed to determine the extent of anisotropy present in 3D-printed materials. Specimens were printed with varying raster ([+45/−45], [+30/−60], [+15/−75] and [0/90]) and build orientations (flat, on-edge and up-right) to determine the directional properties of the materials. Tensile and Iosipescu shear specimens were printed and loaded in a universal testing machine utilizing two-dimensional (2D) DIC to measure strain. The Poisson’s ratio, Young’s modulus, offset yield strength, tensile strength at yield, elongation at break, tensile stress at break and strain energy density were gathered for each tensile orientation combination. Shear modulus, offset yield strength and shear strength at yield values were collected for each shear combination.FindingsResults indicated that raster and build orientations had negligible effects on the Young’s modulus or Poisson’s ratio in ABS tensile specimens. Shear modulus and shear offset yield strength varied by up to 33 per cent in ABS specimens, signifying that tensile properties are not indicative of shear properties. Raster orientation in the flat build samples reveals anisotropic behavior in PC specimens as the moduli and strengths varied by up to 20 per cent. Similar variations were observed in shear for PC. Changing the build orientation of PC specimens appeared to reveal a similar magnitude of variation in material properties.Originality/valueThis article tests tensile and shear specimens utilizing DIC, which has not been employed previously with 3D-printed specimens. The extensive shear testing conducted in this paper has not been previously attempted, and the results indicate the need for shear testing to understand the 3D-printed material behavior fully.

An Investigation on the Softening Mechanism of 5754 Aluminum Alloy during Multistage Hot Deformation

Isothermal interrupted hot compression tests of 5754 aluminum were conducted on a Gleeble-3500 thermo-mechanical simulator at temperatures of 350 °C and 450 °C, and strain rates of 0.1 s−1 and 1 s−1. To investigate the metadynamic recrystallization behavior, a range of inter-pass delay times (5–60 s) was employed. These tests simulated flat rolling to investigate how softening behaviors respond to controlled parameters, such as deformation temperature, strain rate, and delay times. These data allowed the parameters for the hot rolling process to be optimized. The dynamic softening at each pass and the effect of metadynamic recrystallization on flow properties and microstructural evolution were analyzed in detail. An offset yield strength of 0.2% was employed to calculate the softening fraction undergoing metadynamic recrystallization. A kinetic model was developed to describe the metadynamic recrystallization behaviors of the hot-deformed 5754 aluminum alloy. Furthermore, the time constant for 50% recrystallization was expressed as functions related to the temperature and the strain rate. The experimental and calculated results were found to be in close agreement, which verified the developed model.

Modelling and simulation of local mechanical properties of high silicon solution-strengthened ferritic compacted graphite iron

This study focuses on the modelling and simulation of local mechanical properties of compacted graphite iron cast at different section thicknesses and three different levels of silicon, ranging from about 3.6% up to 4.6%. The relationship between tensile properties and microstructure is investigated using microstructural analysis and statistical evaluation. Models are generated using response surface methodology, which reveal that silicon level and nodularity mainly affect tensile strength and 0.2% offset yield strength, while Young′s modulus is primarily affected by nodularity. Increase in Si content improves both the yield and tensile strength, while reduces elongation to failure. Furthermore, mechanical properties enhance substantially in thinner section due to the high nodularity. The obtained models have been implemented into a casting process simulation, which enables prediction of local mechanical properties of castings with complex geometries. Very good agreement is observed between the measured and predicted microstructures and mechanical properties, particularly for thinner sections.

Effects of angular misalignment on material property characterization by nanoindentation with a cylindrical flat-tip indenter

Abstract

Effects of pressure on microstructure and mechanical properties of SiCp/2024 Al-based composites fabricated by powder thixoforming

SiCp/2024 composites were fabricated by powder thixoforming, and the effects of pressure on the microstructure and mechanical properties were studied. The results indicate that the pressure applied during thixoforming affected the secondary solidification behavior by altering the solidification rate, microstructure compactness, plastic deformation, loading capacity of SiCp, and thus the fracture regimes and the mechanical properties. The tensile strengths increased as the pressure increased from 128 to 224 MPa because of the improved compactness, enhanced work hardening and loading capacity of SiCp, and increased concentration of the θ-phase and then decreased owing to the serious stress concentration and θ-phase harmfulness. The composite thixoformed under 224 MPa exhibited the largest improvements, with an ultimate tensile strength of 388 MPa, a 0.2 % offset yield strength (YS) of 297 MPa, and an elongation of 3.8 %, which were increased by 29.3 and 35 % and decreased by 63.5 %, respectively, compared with those of the 2024 alloy. The increment in the tensile strength was due to the synergetic contributions resulting from the strengthening mechanisms of load transfer, thermal mismatch, geometrically necessary dislocations, and grain refinement.

Fabrication of Nano-SiC Particulate Reinforced Mg-8Al-1Sn Composites by Powder Metallurgy Combined with Hot Extrusion

Nano-SiC particulates (n-SiCp) reinforced Mg-8Al-1Sn (AT81) composites with different volume fractions (0, 0.25, 0.5 and 1.0 vol.%) were fabricated by powder metallurgy process (P/M) combined with hot extrusion. The mechanical properties of the composite increased as the n-SiCp content increased until the n-SiCp content exceeded 0.5 vol.%, at which point they began to decrease. For this reason, the 0.5 vol.% n-SiCp/AT81 composite was considered optimal. The 0.2% offset yield strength (YS), ultimate tensile strength (UTS) and elongation (e) of 0.5 vol.% n-SiCp/AT81 composites increased from 175, 318 MPa and 4.5% to 239, 381 MPa and 8.3%, respectively, compared to AT81. Both, the strength and plasticity of the 0.5 vol.% n-SiCp/AT81 composites were improved as well. The improvement in mechanical properties can be attributed to the progressively refined matrix grain size, relatively uniform distribution of n-SiCP and the well-bonded interfaces between n-SiCp and the matrix.

Enhancing overall static/dynamic/damping/ignition response of magnesium through the addition of lower amounts (

This study examines Mg-Y binary alloys synthesized using disintegrated melt deposition technique and secondarily processed by hot extrusion. The alloys were subjected to ignition, damping and tensile tests to determine the effect of low Y content addition on the properties of Mg. Further, the alloys were also subjected to low and high strain rates of approximately 8.33 × 10−5 s−1 and 1.3 × 103 s−1 in compression to elucidate the effect of yttrium addition on dynamic response of magnesium. The results of microstructural characterization revealed a progressive reduction in grain size of magnesium with the increasing presence of yttrium. Transmission electron microscopy revealed the presence of Mg-Y phases irrespective of the limited amount of yttrium. Results of mechanical characterization revealed that increasing presence of yttrium leads to an increase in the ignition temperature, micro-hardness, tensile and compressive fracture strain, 0.2% offset compressive yield and ultimate strength and dynamic strengths with the best values obtained for Mg-1.8Y alloy. An attempt is made in this study to inter-relate the microstructural features with the mechanical response of Mg-Y alloys.

Does plastic suture deformation induce gapping after tendon repair? A biomechanical comparison of different suture materials

Plastic deformation of sutures creates an irreversible extension during load. To test our hypothesis that such plastic deformation causes gap formation after tendon repair, we determined the plasticity of five different suture materials commonly used in tendon surgery. Prolene, Polydioxanone (PDS), Ethibond, Vicryl, and FiberWire sutures were biomechanically tested to determine their offset yield strength, initial extension, creep, relaxed elongation, peak-to-peak displacement, stiffness, and maximum tensile strength under static, constant, and cyclic loading. In addition, 35 porcine hindlimb tendons were used to evaluate gap formation and the biomechanical behavior of the suture materials after tendon repair. Prolene had a low offset yield strength and high initial extensions at 30, 60, and 90N combined with relatively large creep, relaxed elongation, and peak-to-peak displacement. Aside from the low maximum tensile strength and stiffness, these parameters indicate an early plastic deformation during loading. The material properties of PDS were generally better for suturing than those of Prolene, but no difference was found in offset yield strength or initial extension. In contrast to the monofilament materials Prolene and PDS, the braided Ethibond, Vicryl, and FiberWire materials showed significantly less plastic deformation. The lowest amount of plastic deformation was found in the FiberWire and the results for Ethibond and Vicryl were equal. Gap formation occurred at the lowest tension force in the Prolene group, but only FiberWire required a significantly larger tension force to produce gapping at the repair site, indicating a higher resistance to gap formation. The results of this study show that plastic deformation occurs at a lower tension force in the monofilament sutures Prolene and PDS than in the braided materials Ethibond, Vicryl, and FiberWire. After tendon repair, FiberWire likely prevents gap formation, whereas Prolene induces gapping through low-tension plastic deformation. Therefore, plastic deformation should be considered when selecting suture materials for tendon repair surgery.

Mechanical Properties, Short Time Creep, and Fatigue of an Austenitic Steel.

The correct choice of a material in the process of structural design is the most important task. This study deals with determining and analyzing the mechanical properties of the material, and the material resistance to short-time creep and fatigue. The material under consideration in this investigation is austenitic stainless steel X6CrNiTi18-10. The results presenting ultimate tensile strength and 0.2 offset yield strength at room and elevated temperatures are displayed in the form of engineering stress-strain diagrams. Besides, the creep behavior of the steel is presented in the form of creep curves. The material is consequently considered to be creep resistant at temperatures of 400 °C and 500 °C when subjected to a stress which is less than 0.9 of the yield strength at the mentioned temperatures. Even when the applied stress at a temperature of 600 °C is less than 0.5 of the yield strength, the steel may be considered as resistant to creep. Cyclic tensile fatigue tests were carried out at stress ratio R = 0.25 using a servo-pulser machine and the results were recorded. The analysis shows that the stress level of 434.33 MPa can be adopted as a fatigue limit. The impact energy was also determined and the fracture toughness assessed.

Room temperature stress relaxation in nanocrystalline Ni measured by micropillar compression and miniature tension

Abstract

The Assessment of Mechanical Properties of Titanium Sheets Applied to Building Elevations and Roofs

Dynamic development of various industries is tightly coupled with development of new technologies and materials which are increasingly dedicated for a particular application. This regards also titanium materials, which were often applied in aerospace and maritime industries. Gradually their applications spread into automotive, energy, civil engineering industries and medicine. Titanium and its alloys are characterized by unique properties that facilitates their wide adoption in different industries. Initially application of titanium materials was constrained by its high production and processing costs. The factors contributing to application of titanium in civil engineering include high corrosion resistance, low density and low thermal conductivity. High resistance to the elements is very important when durability and long term maintenance costs of a structure are considered. In case of components exposed to action of sea water, acid rains, pollutions, application of titanium materials is advantageous in long term perspective despite its high initial costs. Additionally titanium doesn’t require protective anticorrosive coatings unlike steels and copper. Titanium sheets are applied to large area architectural structures. There are many examples of technical grade titanium applications in building elevations and roofs. For these purposes thin (0.3÷3.0 mm) sheets are selected which allow for weight reduction. In this work properties of commercially pure titanium Grade 2, 3 and 4 were researched. During experimental research the following technological and mechanical properties were determined: offset yield strength Rp02, ultimate tensile strength Rm, elongation A, planar anisotropy Δr, normal anisotropy r, and strain-hardening exponent n.

Rapid microwave sintering of carbon nanotube-filled AZ61 magnesium alloy composites

Abstract In this study, a powder metallurgy processing technique combined with rapid microwave sintering was used to synthesise carbon nanotubes (CNTs) filled AZ61 magnesium alloy composites under ambient conditions, without recourse to any secondary process. In order to determine the appropriate amount of CNTs for taking full advantage of the AZ61/CNTs composite, a powder mixture of the CNTs, in varying volume fractions of 1–3%, and the AZ61 alloy was prepared through a mechanical milling process. The optimized milling intensity allowed for reducing the powder size for effective microwave absorption, and thus improved the dispersion of the CNTs in the Mg alloy matrix without reducing the structural integrity of CNTs. In addition to the incorporation of the CNTs with the dual role of mechanical reinforcement and microwave susceptor, microwave sintering was achieved in only 8 min by using a synergetic combination of graphite and silicon carbide as microwave susceptors in a microwave furnace. The sintered samples, whose porosity ranged between 4 and 6%, were characterised for microstructural, hardness, compressive and fracture properties. The results of hardness and compression tests indicated that these properties of all the composites were significantly improved compared to the monolithic samples. The highest microhardness value (∼105% increment) was recorded for the composite with 3.0% volume fraction of CNTs, while the composite sample with 1.0% volume fraction of CNTs had the highest ultimate compressive yield strength and 0.2% offset yield strength with approximate increments of 59% and 127%, respectively. The failure mechanisms of the composites as compared with the monolithic samples were discussed.

Mechanical Properties and Microstructure of PM Mn-Cr-Mo Steels With Low Carbon Concentration

The effect of chemical composition of the sintering atmosphere on the microstructure and mechanical properties of PM structural low-carbon steels is presented. The base powders were Astaloy CrL, Astaloy CrM, low carbon ferromanganese and graphite C-UF. From the base powders two mixtures with compositions of Fe-3%Mn-(1.5/3%)Cr-(0.2/0.5)%Mo-0.2%C were prepared. Following pressing in a steel rigid die, compacts were sintered at 1250°C for 60 min in a semi-closed container. 5%H2-95%N2mixture and air were the sintering atmospheres. For sintering in air, lumps of ferromanganese were placed with the compacts in the container. After sintering, half of the samples were tempered at 200°C for 60 minutes in air. Mechanical tests (tensile, bend, toughness, hardness) and microstructural investigations were performed.The microstructures of the steels were inhomogeneous, mainly ferritic-bainic. Tempering of steel based on Astaloy CrM sintered in an atmosphere of 5% H2-95% N2slightly reduced tensile strength and toughness: from 748 to 734 MPa and from 7.15 to 6.83 J/cm2, respectively. Chemical composition had a greater effect; steels based on Astaloy CrL and Astaloy CrM had tensile strengths 526-665 and 672-748 MPa, hardness 280-325 and 388-421 HV, respectively. The best properties were obtained after sintering in air of Fe-3%Mn-3%Cr-0.5%Mo-0.2%C without heat treatment: tensile strength 672 MPa, toughness 6.93 J/cm2, hardness 421.1 HV, 0.2 % offset yield strength 395 MPa.

Calcium phosphate–titanium composites for articulating surfaces of load-bearing implants

Calcium phosphate (CaP)–titanium (Ti) composites were processed using a commercial laser engineered net shaping (LENS™) machine to increase wear resistance of articulating surfaces of load-bearing implants. Such composites could be used to cover the surface of titanium implants and potentially increase the lifetime of a joint replacement. It was hypothesized that adding calcium phosphate to commercially pure titanium (CP-Ti) and Ti6Al4V alloy via laser processing would decrease the material loss when subjected to wear. This added protection would be due to the in situ formation of a CaP tribofilm. Different amounts of CaP were mixed by weight with pure Ti and Ti6Al4V powders. The mixed powders were then made into cylindrical samples using a commercial LENS™-750 system. Microstructures were observed and it was found the CaP had integrated into the titanium metal matrix. Compression test revealed that CaP significantly increased the 0.2% offset yield strength as well as the ultimate compressive strength of CP-Ti. It was found that the addition of CaP to pure titanium reduced the material loss and increased wear resistance. This was due to the formation of CaP tribofilm on the articulating surface. The in situ formed tribofilm also lowered the coefficient of friction and acted as a solid lubricant between the two interacting metal surfaces. Overall, CaP addition to Ti and its alloy Ti6Al4V show an effective way to minimize wear induced damage due to the formation of in situ tribofilm at the articulating surface, a strategy that can be utilized in various biomedical devices.

Sample-free control of the mechanical properties of aluminum-based alloys with rare-earth metal additions

A technique is developed for sample-free control of the 0.2 offset yield strength and the ultimate tensile strength of aluminum alloys with rare-earth metal additions using indentation with a spherical indenter.

The Effect of Processing Parameters on Microstructure and Mechanical Properties of Sintered Structural Steels Based on Prealloyed Powders / Wpływ Parametrów Wytwarzania Na Strukturę I Własności Mechaniczne Spiekanych Stali Wykonanych Na Bazie Proszków Stopowych

The object of the study was to evaluate the effect of production parameters on the structure and mechanical properties of Cr and Cr-Mo PM steels. The measurements were performed on sintered steels made from commercial Höganäs pre-alloyed powders: Astaloy CrA, Astaloy CrL and Astaloy CrM mixed with carbon, added in the form of graphite powder grade C-UF.Following mixing in a Turbula mixer for 30 minutes, green compacts were single pressed at 660 MPa according to PNEN ISO 2740 standard. Sintering was carried out in a laboratory horizontal furnace at 1120°C and 1250°C for 60 minutes, in 5%H2-95%N2atmosphere. After sintering, the samples were tempered at 200°C for 60 minutes in air. The steels are characterized by ferritic - pearlitic, bainitic - ferritic and bainitic structures.Following mechanical testing, it can be assumed that steel based on Astaloy CrA pre-alloyed powder could be an alternative material for steels based on Astaloy CrL powder. These steels sintered at 1250°C with 0.6% C had tensile strengths about 650 MPa, offset yield strengths about 300 MPa, elongations about 8.50 %, TRSs about 1100 MPa, hardnesses 220 HV.

Property enhancement of soy protein isolate-based films by introducing POSS

To enhance the mechanical and water-resistant properties of soy protein isolate (SPI) based films, hydrophobic TriSilanolPhenyl polyhedral oligomeric silsesquioxanes (POSS) was incorporated to modify the SPI films. POSS has three SiOH groups in a molecular, which is employed to cross-link SPI with the help of 3-glycidoxypropyltrimethoxysilane (GPTMS). POSS is a structure of eight phenol groups, playing a critical role in improving the physical and mechanical properties. The X-ray diffraction (XRD) and attenuated total reflectance (ATR) Fourier transform infrared spectroscopy (FT-IR) were used to characterize the films. The degree of reaction of SiOH groups in the POSS was estimated to be 53.0% according with the absorbance of ATR FT-IR spectra. Although the elongation at break was reduced by 52.6%, the tensile modulus, tensile strength and 10% offset yield strength were significantly increased by 86.6%, 34.0% and 56.8%, respectively, due to the cross-linking reactions among SPI, GPTMS and POSS. The results of water-resistant tests showed that the 24-hour water absorption was dramatically reduced by 54.7%.