Ultimate Tensile Strength Of Specimens Research Articles

Effects of heat treatments on the microstructure and mechanical properties of Inconel 718 alloy fabricated by electron beam freeform fabrication

The present study investigated the effects of different heat treatments on the microstructure and mechanical properties of Inconel 718 alloy fabricated by electron beam freeform fabrication. The Laves phases, γʹ phases, and (Nb,Ti)C particles were precipitated in the as-deposited specimen. Solution at 960 °C promoted the partial dissolution of Laves phases and the precipitation of δ phases. Further increasing the solution temperature to 1060 °C dissolved the Laves phases effectively, facilitating the adequate precipitation and uniform distribution of γʹ and γʹʹ phases during the subsequent double aging heat treatment. The ultimate tensile strength (UTS) and elongation of the as-deposited specimen were 770 MPa and 12.2 % respectively. The solution heat treatment at 1060 °C increased the elongation to 38.1 % but decreased the UTS to 734 MPa. The microhardness and UTS of specimens that underwent double aging heat treatment were significantly increased, with the maximum average microhardness and UTS reaching 491 HV0.5 and 1285 MPa, respectively. The undissolved Laves phases and the precipitated δ phases at grain boundaries impaired the ductility. The transformation from single solution or double aging heat treatment to solution plus double aging heat treatment led to a shift from a ductile fracture mode to a mixed ductile and brittle fracture mode.

A novel practical method for the production of Functionally Graded Materials by varying exposure time via photo-curing 3D printing

Functionally Graded Materials (FGMs) are one category of composites suitable for situations requiring conflicting properties in one component. Due to the limitations of conventional manufacturing techniques for FGMs, Additive Manufacturing (AM) as a promising candidate has been widely utilized in recent years. Among AM methods, photo-curing 3D printing is a high-precision method that can produce FGMs. In this article, for the first time, a novel practical technique for printing FGMs is introduced based on changing exposure time without additional cost and equipment. For evaluation, a sample whose layers were printed with different exposure times from 4 s to 46 s with 6 s intervals and a nanoindentation test was conducted to measure Young's modulus in selected layers. The tensile test results illustrated that the average values of Young's modulus and ultimate tensile strength of specimens cured for 46 s were 4.76 and 2.17 times as large as those of cured for 4 s, respectively. Also, the maximum amounts of toughness and elongation belonged to the samples printed with 16 s exposure time. In the final parts, three types of cellular solids were fabricated to show the feasibility of the novel method for building complex components. In addition, compression tests were conducted to reveal the behaviours of samples.

Microstructure and mechanical properties of Ti-3Al-2V alloy by dual wire + arc additive manufacturing

In this study, dual wire + arc additive manufacturing technology was used to fabricate the Ti-3Al-2V alloy with TC4 and TA1 wires. Microstructure and mechanical properties of Ti-3Al-2V alloy were studied. The results show that a Ti-3Al-2V wall component was fabricated successfully without defects, and the microstructure mainly consisted of lamellar α + β. The average ultimate tensile strength of specimen in horizontal/vertical direction was 634 MPa/648 MPa, and meanwhile the average elongation of specimen in horizontal/vertical direction was 7.03%/5.10%. Further, the tensile fracture of Ti-3Al-2V component was a mixture of ductile and brittle microstructure.

Effect of cryo-deformation on structure and properties of CoCrFeNiMn high-entropy alloy

Microstructure evolution in high-entropy alloy CoCrFeNiMn during plane-strain multipass rolling to a thickness strain of 80% at 293 and 77 K was studied. Deformation at both temperatures was found to be accompanied by twinning. At 77 K, twinning was more extensive in terms of the fraction of twinned grains and the length of the twinning stage thereby providing faster kinetics of the microstructure evolution. Micro-shear bands formed in the microstructure of the alloy at the late stages of rolling (at ε ≈ 80% at 293 K and ε ≈ 40% at 77 K). The ultimate tensile strength of specimens rolled at 77 K or 293 K was found to be 1500 or 1200 MPa, respectively while the strength in the initial homogenized condition was 440 MPa. The contribution of various mechanisms to the hardening of the alloy following rolling at 77 K and 293 K was analyzed quantitatively.

Investigation of layer thickness effect on the performance of low-cost and commercial fused deposition modelling printers

Rapid prototyping is one of the common technologies in additive manufacturing. The layer-by-layer mechanism of rapid prototyping allows this technology to rapidly create and print complex geometries from three-dimensional models of any objects. Fused deposition modelling is one of the common processes in rapid prototyping, and its maturity has given birth to full-scale, commercial fused deposition modelling machines, as well as low-cost, fused deposition modelling machines, which are also referred to as three-dimensional printers. This work compares the effect of layer thickness during printing on the tensile and compressive strengths of samples, for commercial and low-cost fused deposition modelling machines. Standard samples based on ASTM D638 and ASTM D695 were prepared for the tensile and compressive tests, with layer thicknesses of 0·3302 and 0·2540 mm, using acrylonitrile butadiene styrene as the printing material. From the tensile tests, specimens prepared using low-cost fused deposition modelling managed to obtain only 41·87 and 54·69% of the ultimate tensile strength of specimens prepared using commercial fused deposition modelling, for layer thicknesses of 0·3302 and 0·2540 mm. Meanwhile, from the compressive tests, specimens prepared using low-cost fused deposition modelling managed to obtain only 75·55 and 73·79% of the ultimate compressive strength of specimens prepared using commercial fused deposition modelling, for the same layer thicknesses. Ultimately, low-cost fused deposition modelling still needs more improvement in order to give better results, compared to the currently available commercial-grade fused deposition modelling printers.

Effect of hot working on microstructure and mechanical properties of TC11/Ti2AlNb dual-alloy joint welded by electron beam welding process

The influence of hot working on the microstructures of TC11/Ti2AlNb dual-alloy joints welded by electron beam welding (EBW) process was investigated. The tensile tests were performed at room temperature for specimens before and after thermal exposure. The results show that the fusion zone of TC11/Ti2AlNb dual-alloy joint welded by EBW is mainly composed of β phase. After deformation and heat treatment, the grain boundaries of the as-cast alloy are broken and the fusion zone mainly consists of β, α2 and α phases. The fusion zone performs poor property in the tensile test. Specimens before and after thermal exposure all fail in this area under different deformation conditions. The ultimate tensile strength of specimens after heat treatment is up to 1190 MPa at room temperature. The joints by water quenching after deformation have better plasticity with an elongation up to 4.4%. After thermal exposure at 500 °C for 100 h, the tensile strength of the specimen slightly rises while the ductility changes a little. SEM observation shows that the fracture mechanism is predominantly transgranular under different deformation conditions.

Effect of Mn Addition on Mechanical Property and Corrosion Behavior in Hot Rolled 19 % Cr Duplex Stainless Steel

The effect of Mn addition on mechanical property and corrosion behavior of hot rolled 19 % Cr duplex stainless steel was investigated. The ultimate tensile strength of specimen decreased from 950 to 840 MPa with increasing Mn content from 3.6 to 5.5 wt.%, and further decreased to 768MPa with Mn content addition up to 8.1 wt.%. The sample with the addition of 5.5 wt.% Mn exhibited the highest elongation up to 43%. The polarization result revealed that higher value of breakdown potentials Eb was obtained with increasing Mn content from 3.6 to 5.5 wt. %, but which decreased with increasing Mn content to 8.1 wt.%. The electrochemical impedance spectroscopy (EIS) spectra showed higher corrosion prevention capability was obtained due to enhancement of polarization resistance with increasing Mn content from 3.6 to 5.5 wt.%.

탄소섬유를 이용한 Polyethylene배관의 전기융착 기술

Fuel gas is an important energy source that is being increasingly used because of the convenience and clean energy provided. Natural gas is supplied to consumers safely through an underground gas-pipe network made of a polyethylene material. In electrofusion, which is one of the joining methods used, copper wire is used as the heating wire. However, it takes a long time for fusion to occur because the electrical resistance of copper is low. In this study, therefore, electrofusion was conducted by replacing the copper heating wire with carbon fiber to reduce the fusion time and improve the production when joining large pipes. Fusion and tensile tests were performed after the electrofusion joint was made in the polyethylene pipe using carbon fiber. The results showed that the fusion time was shorter and the temperature inside the pipe was higher with an increase in the current value. The ultimate tensile strength of specimens was higher than that of virgin polyethylene pipe, except for polyethylene pipes joined using a current of 0.8 A. The best fusion current value was 0.9 or 1.0 A because of the short fusion time and lack of transformation inside the pipe. Thus, it was shown that carbon fiber can be used to replace the copper heating wire.

Minimizing scatter in load-controlled fatigue test data of textile polymer matrix composites using statistical techniques

Polymer matrix composites are composed of fiber reinforcement and polymer matrix. Fiber reinforcement is major load carrying component whereas matrix transfers load between the fibers. Fiber reinforcement in the form of textile fabric is popular in the composite industry. Fibers in textile form exhibit good out of plane properties, and good fatigue and impact resistance. The variety of fabric architectures includes weaves, knits, braids, and stitched fabric. Mechanical properties of the composites are dependent on fiber volume percentage and fiber orientation angle. Composites manufactured using low-cost vacuum infusion processes typically have varying fiber volume percentage from location to location and there exists some degree of fiber misalignment. In load controlled fatigue test, fatigue stress is applied as percentage of average ultimate tensile strength (UTS). Due to variation in fiber volume percentage and misalignment in fibers the UTS varies from specimen to specimen. The variation in the UTS between the specimens causes relatively large scatter in the fatigue data. The scatter can be confirmed on stress-cycle (S / Su − N) diagram. Stress-cycle diagram is major tool in predicting fatigue life of the composites. The large scatter in this diagram causes erroneous predictions. The large scatter is because of the considerable difference between average UTS and specimen’s actual UTS. It is necessary to apply fatigue stress based on specimen’s actual UTS. Since, evaluation of UTS is a destructive test there is need to predict UTS of specimen using some analytical tool. In this research braided fabric which is one of the forms of textile fabrics, was used in vacuum assisted resin transfer molding (VARTM) to produce flat composite panels. It was observed that the UTS is a function of the braid angle and fiber volume percentage. Using statistical approach an equation is derived for UTS as function of braid angle and fiber volume percentage. It is suggested that braid angle and fiber volume percentage be measured on each specimen. Then compute UTS of that specimen using derived equation. Then apply fatigue stress based on this computed UTS. This approach would minimize scatter in fatigue data. This approach can be used for any type of composites where UTS is dependent on multiple factors such as fabric orientation angle and fiber volume percentage.