Papers by Keyword: Combined Stress

Abstract: Water culture experiment was adopted to investigate the effects of U and Cod combined stress at different concentrations on the uptake and accumulation of U and Cod and physiological and biochemical characteristics in wheat seedlings. The experiment results showed that the U and Cod uptake by wheat seedlings was higher in roots than in aboveground parts when the total concentration of U and Cod was 5 mg/kg or 20 mg/kg, and the transfer factors (TFs) of U and Cod in wheat seedlings were above 1 when the total concentration was 100 mg/kg. But low concentration of U and Cod were rarely accumulated in wheat seedlings, indicating that wheat seedlings have good tolerance to U and Cod combined stress at low concentration. The experiment results also showed that with the increase in the total concentration of U and Cod, the root activity of wheat seedlings first increased and then decreased, and it exhibited a significant increase when the concentration was 20 mg/kg. Also, with the increase in concentration, the chlorophyll content of wheat seedlings first increased and then decreased, while the SOD activity first decreased and then increased.

Abstract: Fatigue tests of Zr-based bulk metallic glass plates were conducted under cyclic-torsion, and the results were compared with those obtained under cyclic-bending and axial-loading. The fatigue strength of axial-loading was lower than that under cyclic-bending because the fatigue strength depends on the cooling rate in the casting process of the material, which is different in the thickness direction. The fatigue strength of plane-bending reflects the strength at the specimen surface while that of axial-loading is determined by the weakest strength in the thickness direction. For cyclic torsion of specimens with rectangular cross-section, the fatigue crack initiation site must be determined by the ratio of specimen width to specimen thickness, and fatigue strength depends on the ratio. Therefore, the criteria for fatigue limit under combined stress for metallic glass should be constructed considering the crack initiation site.

Abstract: This work focuses on determining the influence of mixed stress conditions on the initiation of fatigue cracks from corrosion pits in a UNS S31603 stainless steel. Fatigue limit was established as a threshold stress criteria for fatigue crack initiation from semi-elliptic surface pits. The strain energy release rate range (G) around semi-elliptic surface pits was determined as a function of the pit aspect ratio (depth/major width axes: a/c), pit contour and the orientation of the nominal stress from a linear elastic fracture mechanics approach. Results indicated that stress conditions for crack initiation in mixed mode overcome the minimum stress level or single threshold stress established from the fatigue limit concept. Under mixed mode condition a crack will grow at the surface zone (φ = 0˚) when a/c ≥ 0.60 and for orientation angles from 5˚ to 75.

Abstract: The effects of temperature and strain rate on flow stress of a highly ductile acrylic adhesive were investigated by performing tensile lap shear experiments on an adhesively bonded single-lap joint, as well as torsion experiments on a tubular butt-joint at temperatures ranging from 10 to 40oC at various shear strain rates. The flow stress decreases considerably with decreasing strain rate and with temperature rise. The stress-strain responses under multi-axial stress conditions were also examined by performing combined tension-torsion experiments on the butt-joint. A constitutive model of temperature-dependent elasto-viscoplasticity that describes multi-axial stress-strain behavior of the adhesive is presented.

Abstract: A unified method is presented for the prediction of the fatigue strength of steel components containing small holes and being subjected to combined loading. Materials investigated were an annealed 0.37% carbon steel and a quenched and tempered Cr-Mo steel. Combined axial and torsional fatigue loading tests were carried out using specimens containing a small hole, which was introduced into the surface by drilling. The diameter of holes equaled the depth and was either 100µm or 500µm. The non-propagating cracks emanating in the radial direction from the holes were observed at the fatigue limit. When the loading condition is the same, they were on a plane that inclined at the same angle with respect to the specimen axis, regardless of the size of holes. This result suggested that the fatigue strength would be controlled by the Mode I threshold condition for propagation of a crack initiated on a critical plane. A criterion connecting uniaxial fatigue strength with multiaxial fatigue strength was proposed based upon the assumption that at the threshold level, the variation of the stress intensity factor of a Mode I crack initiated under combined loading equaled that under uniaxial loading. The predictive method proposed based upon this criterion is practical in that no fatigue test is necessary in making predictions. For the various conditions of in-phase and out-of-phase fatigue loadings with an imposed mean or static load, experimental results agreed well with predictions.

Abstract: Fracture strength of WC-12Co thermal sprayed coating is investigated experimentally and analytically. In the experiments, one pair of butt cylindrical specimen with coating is subjected to combined tension with torsion stresses. Fracture loci were obtained for three kinds of thickness of the coating in σ-τstress plane. Stress distributions at crack tip singular point on fractured surfaces are analyzed by Finite-Element-Method and approximated by the expression σ＝KR-λ where R means normalized thickness coordinate. It is found that the normal stress distributions are common to all cases of testing stress conditions and so fracture condition of the brittle coating is represented as K≧Kcr in the normal stress distribution even under mixed deformation mode I and III. A critical shear stress distribution for separation could also be obtained