Papers by Keyword: V-Notch

Abstract: The previous Measurement of fracture toughness test by using bright indentation for precracked beam method (ASTM C1421) was found difficult to be carried out due to difficulty in precrack generation and measurement of the crack size. In this research single edge precrack V-notch beam (SEPVNB) is introduced as an alternative to solve the problem from previous standardized method. A real crack that can created with referred size is recognized as the best condition for fracture toughness test. The material prepared for this purpose was silicon nitride (Si₃N₄) produced by CeramTec (Plochingen, Germany) under the name SL200 B. It is a gas pressure sintered ceramic containing 3 wt.% Al₂O₃ and 3 wt.% Y₂O₃. The V Notch was prepared by using razor blade with diamond paste following ISO/FDIS 23146 standard preparation with more addition on precrack introduction. The precrack was introduced by so called opposite roller loading. The fracture toughness test was carried out by following procedure in ISO/FDIS 23146 . The result then was compared for validation with both single edge V-notch beam standard (ISO/FDIS 23146 ) and Surface crack in Flexure SCF (ASTM C 1421). The result of fracture toughness by using method that is introduce in this research is found 5.8270.275 MPa^1/2 which is close to the result of SCF (5.335 0.222 MPa^1/2). Meanwhile the value of fracture toughness by using V-notch beam is 4.9130.098 MPa^1/2

Abstract: Sharp V-notches with various angles often appear in engineering structures. When being loaded, the high stress at the apex could result in crack propagation on the structure and further fracture. For this reason, safety evaluation should be emphasized for products or engineering structures with such geometric characteristics. Sharp V-notches are regarded as wedge structures that the above situations seriously and often appear on brittle materials. Regarding the stress intensity factor K of the driving force for wedge structure failure, Chen, Dunn, and Seweryn, with numerical analysis for the fracture experiment, explained that the critical stress intensity factor K_c for single isotropic material fracture could be the intensity failure specification for wedge structures. Nevertheless, V-notched brittle materials are likely to receive great stress over the surface elastic energy of the structure when being loaded, causing brittle failure at the apex. When the high-strength and light-weight composite material is attached to reinforce the surface of brittle materials, the energy is reinforced to enhance the critical stress intensity factor of the overall structure, aiming to improve the failure of brittle materials resulted from stress singularity. This paper therefore tends to discuss the effects of the composite attachment, layer, and fiber reinforced direction on the critical stress intensity factor when the structure is being fractured.

Abstract: The problem of mixed mode (I+III) brittle fracture of polycrystalline graphite is investigated systematically here for the first time. The present study considers cylindrical specimens weakened by circumferential notches characterized by different acuities. A new complete set of experimental data is provided considering different geometrical configurations by varying the notch opening angle and the notch tip radius. The multiaxial static tests have been performed considering different values of the mode mixity ratio. A criterion based on the local Strain Energy Density previously applied by the same authors only to pure modes of loading is extended here to the case of tension and torsion loadings applied in combination.

Abstract: The article deals with an alteration of mechanical properties of plasma nitrided steel. Experimental work was focused on evaluation of influence of plasma nitriding process on the notch toughness of steel. Experiments were realized on V-notch samples of size 10x10x55 mm (according to ISO 148-1 standard) from 14NiCr14 steel. The 14NiCr14 steel was heat treated prior plasma nitriding. The heat treatment consisted of hardening at 850 °C and tempering on elimination of internal stress at 200 °C. Heat treated experimental samples were plasma nitrided at 450 °C, 500 °C and 550 °C. The notch toughness tests of steel were carried out using the instrumental Charpy hammer at test temperatures-40 °C, +21 °C and +70 °C. The notch toughness of plasma nitrided samples achieved nearly identical values as heat treated samples thus plasma nitriding did not reduce the values of notch toughness. The increase in temperature of the plasma nitriding process even led to achievement of higher values of notch toughness compared with heat treatment specimens namely at all test temperatures.

Abstract: In this paper a volume criterion based on a simple scalar quantity, the mean value of the strain energy (SED), has been used to assess the static strength of notched components made of Polymethylmethacrylate (PMMA). The local-strain-energy based approach has been applied to a well-documented set of experimental data recently reported in the literature. Data refer to blunt U-notched cylindrical specimens of commercial PMMA subjected to static loads and characterised by a large variability of notch tip radius (from 0.67 mm to 2.20 mm). Critical loads obtained experimentally have been compared with the theoretical ones, estimated by keeping constant the mean value of the strain energy in a well-defined small size volume. In addition, some new tests dealing with V-notched specimens with end holes have been carried out to investigate the effect of the notch opening angle.

Abstract: The contribution is focused on estimation of a critical value of generalized stress intensity factor for crack propagation from sharp V-notches. Stress distribution around the tip of the V-notch is described on the base of generalized linear elastic fracture mechanics, because V-notch is a singular stress concentrator with stress singularity exponent different from 0.5 (depending on V-notch opening angle). Then also stability criteria based on strain energy density factor and average critical stress are generalized for the stress singularity different from 0.5. Using FE analysis the critical stresses for crack initiation was estimated and compared with experimental data from the literature.

Abstract: Brittle fracture of polycrystalline graphite under tension, in-plane shear and torsion loading is studied experimentally and theoretically using prismatic and axisymmetric specimens weakened by sharp and rounded-tip V-notches. The main purpose is twofold. First, to provide a new set of experimental data from notched samples made of isostatic polycrystalline graphite with different values of notch opening angles and root radii, which should be useful to engineers engaged with static strength analysis of graphite components. At the best of authors' knowledge, data from notch specimens are very scarce in the literature for this material. Second, to apply a fracture criterion based on the strain energy density (SED) averaged over a well-defined control volume surrounding the notch tip, extending what was made by the present authors for in-plane tension-shear loading conditions in notched specimens made of other materials. Good agreement is found between the experimental data related to the critical loads to failure and the theoretical assessments based on the constancy of the mean SED over the material-dependent control volume.

Abstract: The tip radius ρ, depth t and field angle α of notch and the geometrical sizes a and b of shaft are looked as descriptive parameters in the annular notched shaft. Taken the crack, blunt crack and notch as breach, the stress field and displacement field near the tip of breach which serve dimensionless factor f_α(a/b) as descriptive parameter are obtained. The effects of parameters ρ, t and α to f_α(a/b) are analyzed. The connections between stress intensity factor of crack and stress concentrator factor of notch, between sharp V-notch and crack, between V-notch and U-notch have been founded.

Abstract: This work focuses on the fatigue behaviour of notched Ti-6Al-4V titanium alloy in inert environment. V-notched flat samples were cycled under axial fatigue (R = 0.1) under inert conditions by immersion in paraffin oil. A step-loading technique was used to determine the fatigue limit at the complete fracture for a constant fatigue life of 2×10⁵ load cycles. The results were compared with previous data obtained with tests carried out in air and 3.5 wt.% NaCl solution. Fracture surfaces were examined under stereoscopic microscope.

Abstract: Extensive studies have been carried out to deal with the stress singularity of V-notch problems in linear elasticity theory. In fact, the plastic deformation consequentially arises in the notch tip region because of the high stress concentration. The solution of linear elasticity is not adequate to explain the fracture failure of V-notch structures. Because of the difficulties of the nonlinear analysis and the singularity behavior, few results are given for the plastic stress singularities of general V-notch structures. In this paper, the plane V-notch structures in a power law hardening materials are considered. The Von Mises yield criterion and the plasticity total theory are adopted when the materials arise in plastic status. Similar to methods used in the elastic analysis, the plastic stress field near V-notch tips is assumed as an asymptotic expansion with respect to the radial coordinate originating from the notch tip. The governing equations of plastic behavior of plane V-notch are transformed to eigenvalue problems of nonlinear ordinary differential equations (ODEs) contained by the stress singularity order and the associated eigenfunctions. Consequently all of the stress singularities who are less than zero and the associated eigenvectors are accurately determined for the plane V-notches with arbitrary opening angle.