Papers by Keyword: Notch Sensitivity

Abstract: In this study, the Drucker yield function and S-shaped strain hardening model are employed to describe the yielding and hardening behaviors of SUS304 respectively. An uncoupled ductile fracture criterion is calibrated and then utilized to construct the fracture locus of SUS304. To explore the effect of various notches on the prediction of ductile fracture, the constitutive models and ductile fracture criterion are then introduced into the ABAQUS/Explicit code to predict the onset of ductile fracture of various notched specimens. The comparison demonstrates that the ductile fracture criterion captures the fracture strains for all specimens with different notch radius accurately and the finite element models predict the strain distribution, strain evolution and load-stroke curves with good agreement for specimens with large notch radius compared with the experimental results.

Abstract: Glass fiber reinforced thermoplastics and thermosetting composites were prepared in this study. Commercial grades of 20% glass fiber filled polypropylene, polyoxymethylene, polyamide 6 and polycarbonate were injection molded to dumbbell specimens. The specimens are referred as GF/PP, GF/POM, GF/PA and GF/PC, respectively. 55% GF reinforced novolak composites were fabricated by hand lay-up, which different curing times of 20 s, 35 s and 50 s. Mechanical properties, fracture behavior and morpgology of GF composites with and without notched were investigated. GF/PA showed the highest properties of tensile properties, notched strength and fracture toughness as compared to all of GF reinforced thermoplastics in this research. On the other hand, tensile properties and fracture toughness of GF reinforced novolak increased with increasing curing times. SEM photographs indicated ductile fractured surface near the crack edge while their brittle appeared at far of the crack in GF reinforced thermoplastics. It can be noted that notched sensitivity of GF reinforced thermoplastics was lower than GF reinforced thermosetting composites.

Abstract: The high cycle fatigue response of Ti-45Nb alloy was investigated by using an ultrasonic fatigue testing system. The effect of notch geometry on the fatigue response was studied on samples with different circumferential grooves. The experiments showed a decrease of fatigue notch sensitivity with decreasing the notch radius. Finite element analysis (FEA) was conducted for calculation of the stress distribution in the samples and interpretation of the experimental results. Further, the lifetime of the alloy showed a strong dependency on the location of the defects and microstructural inhomogeneities. It was observed that at the same stress amplitude, early failure was caused by surface defects, while those with a longer lifetime failed due to cracks originating from internal flaws.

Abstract: Polymer blends of poly (acrylonitrile-butadiene-styrene)/poly (methyl methacrylate) with ethylene methacrylate copolymer (EMA) were injection molded, and the notch sensitivity of the bends were examined by Izod impact and tensile tests. Investigations revealed that the toughness of ABS/PMMA composites were greatly improved and appeared a linear increase with the addition of EMA. However, the blends also show strong notch sensitivity due to the EMA component but the EMA content seems not a factor responsible for it. Tensile tests of the blends revealed that notches in any depth have great detrimental effects on the elongation at break of the materials, which is not consistent with the calculated notch sensitivity factor (k_S) data.

Abstract: To obtain the notch strength of the composite modified double base (CMDB) propellant, three-point bending tests on the single-edge U-notched thin plate specimens and uniaxial tensile tests on standard tensile specimens were carried out at 20°C. Experimental data include three parts in different range of the stress concentration factor K_t of specimens. The stress concentration factor K_t of the specimens have a distinct effect on the notch strength in a specific range. When K_t is less than the notch sensitivity factor K_bN which is approximately equal to 1.35, the notch strength of CMDB propellant is approximately equal to its fracture strength and independent of the stress concentration factor of test specimens. When K_t is upper than 2.41, the notch strength change to be steady to a proper value which associate with the fracture toughness of the propellant . This shows that the CMDB propellant is insensitive to notch. The tensile test data is used to predict the value of the notch strength and notch sensitivity factor,and the prediction fit well with the test results of the notched specimens in a specific range.

Abstract: For industrial applications, many of the damage of textile reinforced flexible composites are due to growth of the defects coming from manufacturing process or generation by static or dynamic load prior to failure. Hence, this work attempt to investigate on tensile behavior and damage initiation mechanisms in woven fabric reinforced flexible composite with single edge notch (SEN) subjected to mono-axial loading. Tensile tests were conducted with a notch depth of 0, 5, 10, 15 and 20mm, respectively. Damage mechanisms have been described and tensile strength, energy absorption was also expressed. Experimental results indicate that the failure progressive in the textile reinforced flexible composite was quite complex and tested material demonstrated significant notch sensitivity.

Abstract: In this research, fatigue behaviour of Ti-6Al-4V alloy was investigated for smooth and notched specimens with stress concentration factor(K_t) 3.6 and 4.1. This investigation was conducted for various diameter bars having different ultimate strength.Rotating bending fatigue test at R= -1 was emploied for this research. Notch sensitivity data was compared with those of steels. The result indicated that the presence of notch in this alloy has a different amount of sensitivity when the notch specimens were subjected to high cycle fatigue (HCF) and low cycle fatigue(LCF) tests.The notch sensitivity of this alloy was shown generally to be much lower than steel alloys with similar ultimate strength values. Therefore,considering the low sensitivity to notch of this alloy, can be recommended for applications with the presence of notch such as biomedical application

Abstract: Fatigue properties of TRIP-aided annealed martensitic steels with chemical composition of 0.2%C, 1.5%Si, 1.5%Mn, 0-1.0%Cr, 0-0.2%Mo, 0-0.05%Nb, 0-18ppmB was examined for application of automotive diesel engine common rail. The steels achieved extremely higher notch fatigue limits and lower notch-sensitivity than the conventional structural steels, especially in steel with boron or without chromium and molybdenum. This was associated with (i) the TRIP effect of a large amount of stable retained austenite and (ii) strain-induced transformed hard martensite which suppressed the crack initiation and growth due to plastic relaxation.

Abstract: Fatigue behaviour of ultrafine-grained copper of purity 99.9 % produced by ECAP technique was studied in a broad region of stress amplitudes. Fatigue strength is by a factor of about 2 higher than that of conventional-grain-size copper in the broad region of fatigue lives from 6x103 to 2x1010 cycles. The grain structure is stable and undergoes only very marginal changes during cycling. Fatigue slip markings on specimen surface follow the trace of the shear plane of the last ECAP pass. Fatigue notch sensitivity is also higher than that of conventional-grain-size copper, but not dramatically. The cyclic stress-strain curve of studied copper is temperature insensitive, while its S-N curve is temperature dependent.

Abstract: Formable ultra high-strength TRIP-aided steel with bainitic ferrite matrix structure (TBF steel) contributes to a drastic weight reduction and an improvement of crash safety of automobile. In this study, fatigue strength of 0.2%C-1.5%Si-1.5%Mn TBF steels was investigated. High fatigue limit was achieved in TBF steels austempered at 400-450oC, containing a large amount of stable retained austenite. The fatigue limit was linearly related with mobile dislocation density, as well as TRIP effect of retained austenite. When compared to conventional martensitic steel, the TBF steel exhibited lower notch-sensitivity or higher notched fatigue performance. Complex additions of 0.5%Al, 0.05%Nb and 0.2%Mo considerably improved the notched fatigue performance, as well as the smooth fatigue strength. This was associated with the stabilized retained austenite and refined microstructure which suppress fatigue crack initiation and/or propagation.