Degradation Of Strength Properties Research Articles

Effect of artificial ageing on microstructural behaviour of friction stir welded AA2014 aluminium alloy joints

Friction stir welding (FSW) of the heat treatable Al alloy causes degradation of strength properties in the as-weld condition due to thermal cycle. Hence, the post weld heat treatment is used to recover the lost joints properties. In this research, the effect of artificial ageing on microstructure characteristics was scientifically studied. The microstructural features were carried out using a microscope. The strength and hardness properties were correlated with the grain size. It was found that the aged joint exhibited higher lap shear strength than the as weld joint due to the formation of equi-axed grains and fine precipitates.

ОСНОВНЫЕ РЕЗУЛЬТАТЫ ОБОСНОВАНИЯ ПРОЕКТНЫХ ПРЕДЕЛОВ ДЛЯ МАТЕРИАЛА ОБОЛОЧЕК ТВЭЛОВ РУ СВБР-100

One of the key tasks for the reactor SVBR-100 project is substantiation of the core elements performance and efficiency. As part of the R & D program to justify the project, a significant amount of work was performed, which confirmed the corrosion resistance of the material of fuel rod claddings (ferric-martensitic (FM) steel) on the basis of 50 thousand hours, the consequences of deviations of the oxygen regime of the coolant from the optimal values were considered. Paper presents the main results of the analysis of fuel rod claddings loading conditions under normal operation, in violation of normal operating conditions and in conditions of hypothetical emergency overheating. It is concluded that the main mechanisms of damage to equipment and core elements in emergency and preemergency situations are associated with the degradation of strength properties with increasing temperature, while corrosion-erosion processes that accelerates with increasing temperature proceed relatively slowly and are limited in time of exposure. Based on the experimental data obtained in the justification of the SVBR project, the nature of the most dangerous emergency processes and the analysis of their consequences, the paper presents proposals for the formulation of key safety criteria for lead-bismuth reactor plants. The approach is based on the establishment of the maximum permissible temperature-time dependences and/or calculated residual deformations of fuel rod claddings made of FM steel.

Degradation of strength properties and its fracture behaviour of TiB2-TiC-based composite ceramic cutting tool materials at the high temperature

Strength retention is important for tool materials at high temperature because cutting temperature in machining is ranged from room temperature to 1000°C. A study examining the strength properties and fracture behaviour of TiB2-TiC-based composite ceramic cutting tool materials is presented at different temperatures. MoSi2 and SiC additives are considered to investigate their effects on the density, microstructure, strength and failure mechanism of composites. It is found that the addition of SiC contributed more to the high-temperature strength of composites than MoSi2, but it did not improve the room-temperature strength, despite grain refinement. The TBAVS8 composite has a flexural strength of 800MPa at room temperature and can retain 75% at 900°C. At room temperature, the fracture behaviour of composites was dominated by the strong bonding of the Ni binder phase. At high temperatures, the softer Ni binder phase was pinned, and its sliding was inhibited by SiC particles, which decelerated the strength degradation.

Residual Mechanical Properties of Fibre Reinforced Concrete after Exposure to Elevated Temperature

This study aims to find out the compressive strength, split tensile strength, flexural strength, bond strength and permeability of steel fibre reinforced concrete subjected to elevated temperatures ranging from room temperature to 800°C. The specimens were exposed to a heating rate of 10°C/min and the target temperature was maintained for 2 hours to achieve a thermal steady state. A total of 210 specimens of plain and fibre reinforced concrete were tested under the test program. Crimped steel fibres were employed in the study at three volume fractions i.e. 0%, 1% and 1.5%. The results show degradation in strength properties with an increase in maximum heating temperature in both plain and steel fibrous concretes. However, when steel fibres are incorporated in the mix, an improvement of fire resistance and crack resistance at elevated temperature was observed. The results indicate a reduced deterioration in residual compressive, split tensile, flexural and bond strengths of fibre reinforced concrete specimens as compared to controlled plain concrete specimens when the temperature was increased from room temperature to 800°C. Residual permeability characteristics of fibre reinforced concrete show better performance than plain concrete.

Analysis and Systematization of Defects Involved in the Mechanical Strength Degradation of β-Spodumene-Based Glass Ceramics

Structural defects in specimens of densely sintered glass ceramics of β-spodumene composition are analyzed and the relation between the defect size and mechanical strength of the material is considered. The failure of specimens is initiated by surface microcracks produced by mechanical grinding; the role of microstructure inhomogeneities in the degradation of strength properties is emphasized.

The application of BS5950: Part 8 of fire limit state design to the performance of ‘old’ structural mild steels

An investigation has been carried out to extend the guidance given in the new British Standard BS5950: Part 8, on fire limit state design, to the refurbishment and fire damage reinstatement of old steel framed, buildings. Structural mild steel produced to BS15 approximately 50 years ago was found to be generally weaker at elevated temperatures than its modern counterpart—BS4360: Grade 43A (BS EN 10025: Grade 430A). However, providing in design calculations due recognition is given to the lower yield stress of old mild steel at ambient temperature, its performance in fire will be as good as that being currently produced. For the present time, it is therefore appropriate to adopt the same relationships between strength, loading and temperature for structural members given in the new Code, with no additional penalties on fire protection thickness should this be necessary. Fire simulation treatments on steel manufactured to BS15 demonstrated that the degradation in strength properties is in agreement with work reported earlier on ‘weak’ mild steel—BS4360: Grade 43A. The results of a similar evaluation on mild steel produced since the 1986 revision of BS4360: Grade 43A are also in line with previous work.

Controlled energy dissipation in fibrous composites I. Controlled delamination

AbstractDelamination mechanisms in continuous fiber reinforced composites were investigated. The concept of controlled interlaminar bonding (CIB) is proposed as a guideline for preparing fiber‐epoxy composite laminates with enhanced fracture toughness without significant degradation in strength properties. The interlaminar bonding was manipulated by several specialized techniques including insertion of delamination promotors and surface modification of laminae. Results indicated that the plane‐strain fracture toughness of E‐glass‐epoxy laminates could be improved by inserting perforated interlaminar films of aluminum, paper, polyester and polyimide, and fabrics. Such interlayers were used to promote delamination which dissipate strain energy by blunting and diverting a propagating crack. The fracture resistance of a laminate was found to be dependent on the degree of delamination. The competition between the growth of delamination cracks and the propagation of a main crack is controlled by the relative magnitude of the interlaminar bonding strength and the lamina cohesive strength. The interlaminar bonding is controlled by the degree of interlayer perforation and the adhesion between interlayer and lamina. The loading direction was found to be very important in dictating the failure processes. Experimental results from several composite systems are presented and discussed along with post‐failure analysis data.