Detection of Hydrogen Damage in 2.25Cr1Mo0.25V by Ultrasonic Inspection

2.25Cr1Mo0.25V steel has better high temperature strength than ordinary Cr-Mo steel, and has been widely used in nuclear and chemical environments such as nuclear energy and chemical industry. However, vanadium-added steel is still likely to cause hydrogen damage and requires early detection. Ultrasonic inspection has strong penetrating ability. It can detect thin plates with thickness of 1-2mm and steel structure of several meters long. In this paper, ultrasonic longitudinal wave was used to detect the amplitude and longitudinal wave period before and after hydrogen charging, and the change of wave velocity was obtained. The dynamic tensile test of the specimen before and after hydrogen charging was also carried out, and the elastic modulus and elongation of hydrogen before and after hydrogen charging were obtained. The relationship between ultrasonic signal and hydrogen embrittlement was also discussed in this paper.

Physico-chemical and mechanical characterization of bambusa vulgaris fibers from Cameroon

In this study on characterization of bambusa vulgaris fibers from Cameroon (BV), we evaluated the linear density as well as the moisture uptake. With the help of SEM, the cross-sections were observed to be circular shapes; they increase from outside to inside in any transverse position along the stem. Also, the degradation temperature of BV was investigated with the aid of TGA and the result showed that the degradation temperature of BV fibers is between 366 °C and 380 °C. In addition, their Young's moduli in dynamic tensile test was determined and it was noticed that the Young moduli increase from inside to outside. The bending tests of BV fibers were carried out and enable the various parameters in zone 3/3. Finally, the creep behavior of BV fibers was studied and it was revealed that the 4-element Burger model describes very well this phenomenon and could help in well predicting fatigue behaviour of BV fibers reinforced composites.

Strain Rate Dependent Mechanical Stability of Retained Austenite in Hot-Rolled Medium-Mn Sheet Steels

The paper presents microstructural and mechanical results of medium manganese steel deformed under high strain rates. The rotary hammer tests at strain rates of 250, 500 and 1000 s-1 were applied. Mechanical properties under dynamic tensile loads were determined. According to the obtained results, when strain rate increased the yield point of the steel increased. An opposite trend was present regarding total elongation. In case of tensile strength, its level is similar for all analyzed deformation rates. The microstructure of the steel after the dynamic tensile test is composed of bainite, martensite and martensitic-austenitic islands. The strain-induced martensitic transformation was identified in microscopic investigations.

Dynamic Tensile Test of Granite and Its Tensile Sensitivity

Through the dynamic splitting tensile test under various loading rates, different mechanical parameters have been analyzed; not only the dynamic peak stress but also the dynamic peak strain has a good linear relationship with the strain rate. The tensile sensitivity obtained from the dynamic tensile test increases with strain rate gradually, and it shows a nearly linear relation, which fully indicates that the granite specimen is a strain rate sensitive material. Moreover, with the numerical simulation, the damage area of the specimen is consistent with the actual failure mode of the specimen. Furthermore, the influenced factor on the dynamic tensile strength is discussed, which illuminates that the most fundamental reason of the rate effect is that the stress wave velocity is faster than the crack propagation velocity in the specimen during the impact process.

Dynamic Tensile Properties of Granite Varied with Depths under a Similar Loading Rate

Based on the SHPB device, the dynamic tensile test was carried out on the granite, which is located at the depth 350 m∼580 m at the same borehole in TianHu area Xinjiang Province, the preselected site of the high-level radioactive waste geological disposal in China. Under the loading rate level of 105 MPa/s, the dynamic tensile strength is generally between 15 MPa∼35 MPa, which is of significant reference for the site selection. No matter whatever the depth, the dynamic tension strength increases with the loading rate, which shows the loading rate effect of brittle material. Meanwhile, the failure model is also tension pattern, which is the same as the static tension test. Furthermore, as the physical characteristics of the rock have been changed gradually, the rock strength and other mechanical properties will increase or decrease with the depth. From the point of physical mechanism, the density, porosity, and others are different at diverse depths, which lead to the differences of mechanical properties. And the result and the theoretical knowledge could be applied to the blasting and excavation of deep geoengineering and HLW geodisposal.

A Comparative Study on the Dynamic Tensile Behavior of Nanostructured Bainitic and Quenched-Tempered Martensitic Steels

In order to assess the dynamic tensile behavior of a newly developed three-step low-temperature-transformed bainitic microstructure, and a conventional one-step isothermal bainitic microstructure, and a quenched and tempered martensitic microstructure, a comparative research was conducted by using the dynamic tensile test. The results showed that more film-like retained austenite was obtained in the three-step low-temperature-transformed sample. The carbon content in the film-like retained austenite was found to be higher as compared to the blocky retained austenite. The dynamic tensile properties were all improved with an increase in strain rates (from 0.1 to 500 s−1). However, the three-step bainitic low-temperature-transformed sample showed the most remarkable dynamic tensile properties, including ultimate tensile strength and total elongation. This is attributed to a better transformation-induced plasticity effect that is exhibited by the higher stability of the film-like retained austenite. Therefore, the present study suggests that performing a three-step low-temperature bainitic transformation promotes grain refinement and the formation of film-like retained austenite and improves the dynamic tensile properties.

Experimental Study on Dynamic Mechanical Properties of Galvanized Iron Wire under Seismic Strain Rate

This paper focuses on the mechanical properties of galvanized iron wire under various conditions of earthquake-type strain rate. The dynamic tensile test of galvanized iron wire was conducted on MTS New 810 electro-hydraulic servo-controlled testing system. The dynamic tensile constitutive relationship of galvanized iron wire was proposed under seismic strain rate. The accuracy of the proposed constitutive relationship of galvanized iron wire was verified by comparing with reinforcing steel.