Improvement Of Toughness Properties Research Articles

Prediction on damage evolution of recycled crumb rubber concrete using quantitative cloud imagine correlation

Abstract To account for the improvement of mechanical properties for recycled crumb rubber concrete (RCRC) under uniaxial compression and flexural toughness test in detail, three groups of RCRC specimen covering contents of rubber aggregate from 10 percent to 30 percent and one group of normal concrete (NC) specimen were prepared. Experimental results present distinguished influence of rubber particle content on uniaxial compressive strength and failure mode. Then, improvement in toughness properties was displayed inherently through change of the index named ratio of flexural strength to compressive one ( R f - c ). Simultaneously, a mesoscopic numerical model on random aggregate of RCRC was built up and validated by comparison of results from damage simulating to in-door testing. Furthermore, the mechanism of ductility enhancement for RCRC is unveiled visually and the prediction on damage evolution is revealed in quantitative way by a novel methodology of quantitative cloud imagine correlation (QCIC) based on 2D analysis. Subsequently, the similar law is established by a 3D Extended QCIC named volumetric damage accumulation method (VDAM). Therefore, it put forward a step further from state-of-the-art research about mechanical properties of RCRC, which may promote the utility of optimal design for this ecological material in civil engineering.

Optimisation and analysis of the reinforcement effect of carbon nanotubes in a typical matrix system

The scope of this work is the analysis of the reinforcement effect of carbon nanotubes in typical matrix systems, such as epoxy resins. As is well known, efficient dispersion is critical in achieving adequate reinforcement. However, dispersion processes are also well known to degrade the nano-phase. Degradation is manifested as reduction in the aspect ratio as the nanotubes de-agglomerate and break at the same time. For the purpose of this study, multi-wall carbon nanotubes (MWCNTs) with typical length of 1 lm and diameter of 10-15 nm were used for manufactur- ing MWCNTs/epoxy nano-composites. The inclusion content was 0.5 and 1 % w/w respectively, and dispersion was performed using a typical sonicator gun. The tensile and the fracture toughness properties of the specimens were initially assessed and subse- quently optimized. The optimisation process resulted in spectacular improvement in toughness properties. Finally, the antagonistic mechanisms that govern the reinforcement efficient were analysed via the applica- tion of the Halpin-Tsai equations for the tensile properties and the distinct contributions of the mech- anisms that dissipate energy and enhance toughness, such as the nanotube pull-out, the plastic void growth of the epoxy and the nanotube debonding energy. The de-agglomeration and the aspect ratio reduction were

Effect of in-plane residual stresses on the post-deflection behaviour of a T-shaped deflected crack in layered systems

Post-deflection behaviour of a T-shaped crack in a bilayer material system under the presence of in-plane residual stress was investigated for a four-point bending configuration. Non-dimensional parameters for generalization of the residual stress state in a bilayer system were defined using globally measurable quantities such as curvatures and axial strains. It was predicted that the residual stress varying from tension at the outer edge to compression at the interface was beneficial to prevent kinking of the T-shaped crack out of the interface and therefore to toughening of the layered composites. However, it was expected that appreciable improvement in toughness properties was possible only when the intact layer is stiffer than the cracked layer. Further, incorporation of residual stresses higher than a certain level did not result in a further improvement in the toughness properties. Criteria for crack deflection-induced toughening of layered composites were derived from these predictions.

Differences in impact values of core and rim in electroslag weld metal: Improvement of toughness properties in ESW weld metal in constructional steels (2nd Report)

Summary The purpose of this paper is to investigate the impact properties of weld metal produced under different welding conditions with special reference to electroslag welding (ESW) as a high heat input welding process generally applied in the fabrication of four‐sided thick‐plate box columns for general multi‐storey buildings. The paper focuses in particular on the impact properties of ESW weld metal at its centre (core (C)) and periphery (rim (R)). The results obtained may be summarised as follows: The vE value of the weld metal core is lower than that of the weld metal rim. The absorbed energy transition temperature is also higher. The vE values of the weld metal core and rim altered with a change in the welding heat input Q (varied at six levels in the 10.1 ∼ 126.7 kJ/mm range), generally decreasing with an increasing heat input. The vE value of the core is lower than that of the rim. In the weld metal produced at the maximum heat input (126.7 kJ/mm), however, the core and rim have much the same vE values. The vE value of the weld metal core shows little change with a change in the steel type (one type of TMCP and two types of SM490A), and remains at a low value. When there is a change in the surrounding gas (oxygen (O2), air, and argon gas), the vE value decreases in an Ar, air, O2 sequence. The weld metal core vE value is little dependent on any change in the flux type (three types of fused flux) and weight of flux used (0.5 or 0.7 N). The microstructural observations suggest that grain‐boundary ferrite (GBF) occurs at the coarse prior austenite grain boundaries of the rim, with fine acicular ferrite (AF) being mainly found trans‐granularly. In the core, grain‐boundary ferrite is formed at high density at the fine prior austenite grain boundaries, with massive polygonal ferrite (PF) being formed at high density transgranularly. There are thus distinct differences in the coarse ferrite morphology of the rim and core. The SEM observations of the fracture surfaces suggest that the core weld metal has a large grain size, a feature corresponding to its low vE value. The observations made at the fracture surface periphery indicate that numerous secondary cracks are initiated in the grain‐boundary ferrite of the core, suggesting that the ferrite has a low toughness. The results of the SEM simultaneous fractographic‐microstructural observations suggest that fracture selectively propagates along the grain‐boundary ferrite. This indicates that the low vE value of the core is due to the presence of high‐density grain‐boundary ferrite and massive transgranular polygonal ferrite.

Improvement of impact properties in the core of electroslag weld metal by variation in welding wire composition: Improvement of toughness properties of ESW weld metal in constructional steels (3rd report)

Summary This paper describes an investigation of improvement of the impact properties of electroslag (ESW) weld metal using different types of welding wire. The tests were conducted with six types of welding wire and three levels of welding heat input, i.e. Q = 45.6, 79.0, and 126.7 kJ/mm. The results obtained may be summarised as follows: When a heat input at any level is applied, irrespective of any difference in the welding wire used, the impact value (vE value (J), 273 K) at the centre (core) is lower than that at the periphery (rim). No major improvement of the vE value of the core is found at Q = 45.6 kJ/mm (single‐layer standard heat input conditions for 40 mm thick plate) when wires A ∼ D are used. However, it is found effective to use Ni‐containing wire F (4.18%Ni) to improve the vE value of the weld metal core at Q = 45.6 kJ/mm. The differences in the vE values of the core and rim are closely related to the size of the prior austenite (γ) grains and the different precipitation conditions of the ...

Structure-property relations and the design of Fe-4Cr-C base structural steels for high strength and toughness

Some design guidelines for improving strength-toughness combinations in medium car-bon structural steels are critically reviewed. From this, quaternary alloy development based on Fe/Cr/C steels with Mn or Ni additions for improved properties is described. Transmission electron microscopy and X-ray analysis reveal increasing amounts of retained austenite in these alloys with Mn content up to 2 wt pct and Ni additions at 5 wt pct after quenching from 1100°C. A corresponding improvement in toughness properties is also found. Grain refining results in a further increase in the amount of retained austenite. In addition, the excellent combinations of strength and toughness in these quaternary alloys are attributed to the production of dislocated lath martensite from a homogeneous austenite phase free from undissolved alloy carbides. The question of thermal instability of retained austenite following tempering is considered in detail and it is shown that the decomposition of retained austenite is closely related to the ease of nucleation and growth of cementite. Thus, graphitizing alloying elements such as Ni are beneficial in postponing the decomposition of retained austenite.