Papers by Keyword: R-Curve

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Authors: Xiang Guo Wu, Sang Mook Han, Sung Wook Kim, Su Tae Kang
Abstract: An R-curve formula for ultra high performance cementitious composites is derived in this paper. The fracture mechanics based on R-curve is used to predict the load-deflection relation of ultra high performance cementitious composites. The reductions of stress intensity factor and CTOD by steel fiber reinforcement are assumed as conforming linear distribution along crack propagation. The effective numbers of steel fiber on unit area based uniform distribution is used here. Results of the theoretical predictions show a good agreement with test results of three point bending beam of UHPCC. The modified R-curve formula for UHPCC can be a reference for future study of fracture performances of UHPCC.
Authors: Hiroshi Kawamoto, Y. Takigawa, K. Hiramatsu, Atsushi Okada
Authors: Jana Špaková, Ján Dusza
Abstract: Study compare R-curve behaviour of silicon nitride obtained using Vickers indented beam specimens and single edge V-notched beam (SEVNB). R-curve measurement realized by Vickers indented beam was reported by Krause. Crack growth using single edge V-notched beam was observed in situ. The indentation experiments, in comparison with SEVNB method revealed higher R-curve values (KR=3.3 – 4.8 MPa.m1/2). The discrepancy in the R-curve results is attributed to inaccuracy related to the determination of indentation toughness. The indentation fracture toughness may include the aspects of crack opening behaviour, residual indentation stress intensity.
Authors: Magdalena Szutkowska, Marek Boniecki
Abstract: The relationship of KR versus crack length c (R curve) for Al2O3-30wt.% Ti(C,N).and for comparison alumina ceramics has been examined. The R-curve has been evaluated using pronounced long-crack formed during the three point bending (3PB) of the double edge notched beam. A combination of in situ microscopic crack growth observation and mechanical testing enabled measurement of crack growth resistance curves. The special device consisting of light microscope coupled with CCD camera, was fitted to Zwick 1446 testing machine. These observations reveal the existence of flat R-curve for Al2O3-30wt.% Ti(CN) and increasing R-curve for pure alumina. A study of slow-crack-growth (SCG) in tested materials was carried. The load-relaxation technique was used for observation at slow-crack-growth. The crack length was evaluated by linear-elastic analysis from the compliance of single-edge-notched specimen in three-point bending test. Parameters of stable crack growth n and logA, work-of fracture (WOF), stress intensity factor at the moment of crack initiation KI0 and maximum values of stress intensity factor KImax were determined. Mechanism of grain bridging responsible for occurrence of R-curve was observed by SEM and TEM.
Authors: Hassan El Attaoui, Malika Saâdaoui, Jérôme Chevalier, Gilbert Fantozzi
Authors: Hideo Awaji, Chun Hong Chen, Nobuyuki Kishi
Abstract: Although porous ceramics are materials with high potential for helping conserve the environment, the characteristics of pore-related mechanical properties have not yet been examined sufficiently. The R-curve behavior of porous ceramics was estimated using the crack stabilizer technique developed by Nojima et al. Also, the critical frontal process zone (CFPZ) size for porous ceramics was estimated from the strength and fracture toughness of the materials used. The results revealed that the R-curve behavior was almost flat in porous ceramics, in contrast with a steeply rising R-curve behavior for porous silicon carbide observed previously, and that the CFPZ size of porous ceramics was larger than that of dense ceramics. A schematic explanation for the crack extension in porous materials was presented to discuss the R-curve behavior of porous ceramics.
Authors: Dong Yun Li, Guan Jun Qiao, Zhi Hao Jin
Authors: Henryk Tomaszewski, Marek Boniecki, Helena Węglarz
Authors: M. Drissi-Habti, Jean-Louis Chermant, Dominique Rouby
Authors: Nikolai Kashaev, Stefan Riekehr, Manfred Horstmann, Volker Ventzke
Abstract: Weight reduction is the main driving force in automotive and aircraft structural design. As a result, magnesium alloys, with their high potential for lightweight construction, have attracted a considerable amount of industrial attention. The determining criterion for the structural applications of magnesium alloys is the availability of efficient joining technologies for the construction of lightweight structures and the availability of reliable data for the assessment of their damage tolerance behaviour. Laser beam welding (LBW), as a high-speed and easily controllable process, allows the welding of complex geometric forms that are optimised in terms of mechanical stiffness, strength, production velocity and visual quality. The work accomplished in this study addresses the challenges of the LBW process for typical joint configurations using the magnesium alloy AZ31HP: butt joints, T joints and overlap joints. LBW processes were developed for use with a 3.3-kW Nd:YAG laser to optimise the mechanical performance of such joints with respect to tensile strength, fatigue, fatigue crack propagation and mechanical fracture behaviour. The relationships between the LBW process and the microstructural and mechanical properties of welds were established. Compared to state-of-the-art aerospace alloys, AZ31HP demonstrates that magnesium alloys have potential for use in structural applications, with AZ31HP being comparable to AA2024T351 and AA6061T6. Welded AZ31HP exhibits better crack resistance than the base material, so fully welded integral structures made from magnesium alloys can be used in lightweight construction.
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