Recovery Of Tensile Properties Research Articles

Investigation of Irradiation Hardening and Effectiveness of Post-Irradiation Annealing on the Recovery of Tensile Properties of VVER-1000 Realistic Welds Irradiated in the LYRA-10 Experiment

Assessing the embrittlement and hardening of reactor pressure vessel steels is critical for the extension of the service lifetime of nuclear power plants. This paper summarises the tensile test results on the irradiation behaviour of realistic VVER-1000 welds from the STRUMAT-LTO project. The welds were irradiated at the HFR (Petten, the Netherlands) to a fluence of up to 1.087 × 1020 n·cm−2, and their irradiation hardening was studied by means of tensile testing. The four grades, with different Mn and Ni contents, show different hardening behaviours. The highest degree of irradiation hardening is observed for the weld that has the highest combined Ni + Mn content. The results show that there is a synergetic effect of Mn and Ni on the irradiation hardening behaviour of the VVER-1000 welds. Besides irradiation hardening, the effectiveness of post-irradiation annealing treatments on the recovery of the tensile properties is studied in the present work. Post-irradiation annealing treatments conducted at 418 °C and at 475 °C proved to be effective for three of the four investigated welds. For the realistic weld with the highest combined Ni + Mn, only the annealing at 475 °C led to the complete recovery of the tensile properties.

Effect of graphene on self-healing performance of hydroxyapatite/polydimethysiloxane composites

ABSTRACT Recently, polymeric self-healing materials are tremendously being exploited in the fields of biomedical and other advanced engineering applications. However, mechanism of the self-healing materials is not very clear and the healing performance is very poor for the existed materials. Therefore in our present investigation, hydroxyapatite (HA) bioceramic, graphene (Gr) and polydimethysiloxane (PDMS) were used to develop a high performance novel self-healing composite. Here, we proposed a single step accessible preparation of short-layers graphene by the exfoliation of graphite layers via acid leaching method. Further, Gr/HA embedded PDMS membranes were prepared using a vascular method. We prepared the PDMS elastomer (resin:hardener ratio = 1:1) being mixed with 2 wt% HA and varying concentrations 0.1 wt%, 0.3 wt%, 0.5 wt% of Gr. The band gap, phase structure, crystalline and chemical structure of the Gr/HA composite films were characterized using UV-Vis, XRD and FTIR studies. A series of tensile tests were conducted to measure virgin and healed tensile specimens. The highest mechanical property was achieved at 2 wt% of HA. But best self-healing performance of the 0.1 wt%Gr composite was obtained from the recovery of tensile properties. The healing efficiency was found to depend on the curing properties of PDMS varied with HA/Gr reinforcement and quantity of healing agent delivered.

In-situ evaluation of self-healing performance of Engineered Geopolymer Composites (EGC) by ultrasonic method

This paper reports a novel method to evaluate the self-healing performance of Engineered Geopolymer Composites (EGC), the ultrasonic method which provides an in-situ evaluation of the samples. The dog-bone shaped samples were pre-loaded to 2% tensile strain at different curing ages (3d, 7d, 14d, and 28d) followed by putting them into 40 °C water for self-healing. Apart from the development of ultrasonic pulse velocity (UPV), the recovery of tensile properties and residual crack characteristics were investigated to verify the effectiveness of ultrasonic method. The results show that there is an increase of UPV in all samples while A7d samples (pre-loaded at 7d) have the highest UPV after self-healing for 28d and the most significant increasing magnitude during the self-healing process indicating great self-healing performance. The similar conclusion could be found according to the traditional indicators’ results of tensile properties and crack characteristics, which validates the effectiveness of ultrasonic method. Besides, there is a strong correlation between the tensile strength and UPV with R2 close to 1, which indicates that UPV could be a prediction to tensile strength according to the fitting equations.

Recovery of tensile properties in helium implanted EUROFER97 by post-implantation annealing

Reduced activation martensitic stainless steel EUROFER97 was homogeneously implanted at 250 °C with 0.25 at.% helium, and was subsequently annealed in vacuum for 10 h at 550 °C and 750 °C, respectively. Tensile testing at room temperature and at 250 °C showed increase in strength and decrease of ductility by the implantation. Both changes recovered during annealing: While the strength was reduced by annealing to values between unimplanted and implanted condition, ductility was increased even beyond that of virgin material. This means, the implanted plus annealed material showed improved behaviour even when compared to the virgin material: higher strength and greater ductility. Including the results on fracture surface and microstructural investigations, a tentative model is presented.