Effect Of Specimen Shape Research Articles

Effect of specimen shape on the behavior of brittle materials using probabilistic and deterministic methods

The main objective of this paper is to verify the activated defect localization under various loading rates for Modified Brazilian Disk (MBD) compared with spherical glass specimen frequently used in the literature. The geometry of specimen can considerably influence the mechanical response of material specially, the brittle materials which are very sensitive to the defects activations and finally corresponding Weibull statistic problematic for these materials. The high and low loading rates have been investigated using universal Instron machine compression and Compressive Hopkinson Pressures Bars (CHPB) on MBD lead glass specimen and then the experimental results have been compared via the Weibull's distribution for scatter strength variation. Finally, we observed the contact problem leading to the activated defects in this area on spherical glass specimen under static and dynamic loading not MBD specimen under both loading rates. Consequently, the probabilistic approach should be taken into account including the specimen geometry and also ‘Type’ of loading application due to the activated defect position arising from the sever contact problem for the brittle materials.

Determination of cohesive laws by the J integral approach

The determination of cohesive laws for describing large scale failure process zones is discussed. Firstly, a general approach for determination of cohesive laws, by the measurement of the J integral and end-opening of the cohesive zone of double cantilever beam specimens loaded with pure bending moments, is described. Next, two case stories are reviewed: failure of adhesive joints and splitting of a unidirectional carbon fibre/epoxy composite. For the adhesive joints, measured failure strengths of bonded panels having a central notch were found to in very good agreement with predictions from cohesive law parameters determined on test specimens. For the problem of splitting of unidirectional composites, micromechanisms were observed in situ during cracking. A cohesive law shape, predicted by a micromechanics model, was found to agree well with macroscopic cohesive law determined by the J integral approach. The cohesive law was used for predicting effect of specimen shape on strength; predictions were confirmed by experiments. Finally, some ideas regarding determination of mixed mode cohesive laws are discussed.

Electromagnetic response of type-II superconductors: effects of specimen shape, field orientation, and London depth

Previous continuum theory of type-II superconductors with and without vortex pinning, of various shapes and in an applied magnetic field, is generalized to account for an applied transport current and a finite London penetration depth λ. The extension to λ>0 is important at low inductions B to describe the transition to the Meissner state, and for films with thickness not much larger than λ. The finite width of the surface layer with screening currents and the correct dc and ac responses in various geometries follow naturally from an equation of motion for the current density, in which the integral kernel now accounts for finite λ.

Flux Conservation Equations of High-Tc Superconductors with Different Shapes and Their Application in Electromagnetic Measurements

In consideration of the importance of the specimen shape effects and field orientations in electromagnetic measurements, we extended the conservation equations of one-dimensional (1D) specimens to two-dimensional (2D) ones in parallel fields, the corresponding parameters were calculated and tabulated. Then we discussed the problem of 2D specimen in a perpendicular field. Based on the derivation of general flux conservation equations, we presented their simple applications in measurements by providing the commonly used measurement equations in typical measurement methods.

Strain-softening of concrete in uniaxial compression

0025-5432/97 © RILEM tory cast its own specimens following a prescribed recipe. The pre-peak behaviour was found to be independent of specimen slenderness when low friction loading platens were used. However, for all loading systems a strong increase of (post-peak) ductility was found with decreasing specimen slenderness. Analysis of the results, and comparison with data from literature, showed that irrespective of the loading system used, a perfect localization of deformations occured in the post-peak regime, which was first recognised by Van Mier in a series of uniaxial compression tests on concrete between brushes in 1984. Based on the results of the Round Robin, a draft recommendation will be made for a test procedure to measure strain softening of concrete under uniaxial compression. Although the post-peak stress-strain behaviour seems to be a mixture of material and structural behaviour, it appears that a test on either prismatic or cylindrical specimens of slenderness h/d = 2, loaded between low friction boundaries (for example by inserting sheets of tef lon between the steel loading platen and the specimen), yields reproducible results with relatively low scatter. For normal strength concrete, the closed-loop test can be controlled by using the axial platen-to-platen deformation as a feed-back signal, whereas for high-strength concrete either a combination of axial and lateral deformation should be used, or a combination of axial deformation and axial load. FOREWORD An extensive Round Robin test programme on compressive softening was carried out by the RILEM Technical Committee 148-SSC “Test methods for the Strain Softening response of Concrete”. The goal was to develop a reliable standard test method for measuring strain softening of concrete under uniaxial compression. The main variables in the test programme were the specimen slenderness h/d and the boundary restraint caused by the loading platen used in the experiments. Both high friction and low friction loading systems were applied. Besides these main variables, which are both related to the experimental environment under which softening is measured, two different concretes were tested: a normal strength concrete of approximately 45 MPa and a higher strength concrete of approximately 75 MPa. In addition to the prescribed test variables, due to individual initiatives, the Round Robin also provided information on the effect of specimen shape and size. The experiments revealed that under low boundary friction a constant compressive strength is measured irrespective of the specimen slenderness. For high friction loading systems (plain steel loading platen), an increase of specimen strength is found with decreasing slenderness. However, for slenderness greater than 2 (and up to 4), a constant strength was measured. The shape of the stress-strain curves was very consistent, in spite of the fact that each laboraRILEM TC 148-SSC: TEST METHODS FOR THE STRAIN-SOFTENING RESPONSE OF CONCRETE

Effects of specimen shape on the measurement of the electromechanical coupling coefficient in inclined electrodes

AbstractThe electromechanical coupling coefficient k can be determined by measuring the frequency characteristics of admittance. However, it is known that the specimen shape affects the measurement of the admittance frequency characteristics. In this paper, the finite element method was employed to investigate the effects of sample electrode inclination on the electromechanical coupling coefficients. The results indicate that the electromechanical coupling coefficients for the stretching vibration mode (31) of a rectangle, the stretching vibration mode (33) of a bar, and the expansion vibration mode (p) of a disk decrease when the sample electrodes are inclined. No spurious vibration was observed in the transverse vibration of (31) and (p) modes when the sample electrodes were inclined. However, a spurious vibration was observed in the longitudinal vibration of the (33) mode. These observations were confirmed by experiment.

Fundamentals of the statistical mechanics of composite systems

The proposed variant of the statistical theory of composite media makes it possible to derive relations between the effective parameters of the medium and the dispersion characteristics of the structure, and also to account for the effect of specimen shape and variable structural heterogeneity on these parameters. In the limiting case of an infinitely large specimen, all relationships comply with the results of the traditional theory of composite systems.

Effect of specimen shape and cyclic loading on tension tests of two epoxy resins

Effect of specimen shape and cyclic loading on tension tests of two epoxy resins

Effect of Specimen Shape and Cyclic Loading on Tension Tests of Two Epoxy Resins

Abstract Cyclic load experiments are reported for two epoxies, one containing rubber particles. With and without interruptions during unloading, the experiments were performed on an Instron machine at a constant rate of head motion using an averaging extensometer capable of strain to fracture and having no dead zone. Results of interrupted unloading tests show the effect of elasticity of the portion of the specimen outside the gage length on the observed stress-strain curves.

部分除荷をほどこした高強度鋼材の遅れ破壊強さにおよぼす試験片形状の影響

部分除荷をほどこした高強度鋼材の遅れ破壊強さにおよぼす試験片形状の影響

Effect of specimen shape on creep response of a frozen sand

The stress—strain and strength behavior of frozen soils is most often studied in a conventional uniaxial or triaxial compression test. However, available experimental evidence shows that the results obtained in such a test may be considerably affected by the test conditions, i.e., by the specimen shape and the method of axial load transfer to the specimen ends, both of which affect the uniformity of stress and strain distribution in the sample. The methods proposed for solving the problem of load transfer to the specimen ends differ considerably for brittle and ductile materials, respectively. Since a frozen soil may behave either as a brittle or as a ductile material, depending on strain rate, temperature and confining pressure, it is considered that the load transfer method selected should correspond to the expected sample behavior. In this paper, the results of a series of compression and creep tests are presented, in which the effects of specimen shape and end conditions on the behavior of a frozen sand were systematically investigated and compared. a frozen sand were systematically investigated and compared.

Effect of specimen shape on creep response of a frozen sand : Ladanyi, B; Arteau, J Proc 1st International Symposium on Ground Freezing, Bochum, 8–10 March 1978, P141–153. Publ: Bochum, Ruhr University, 1978

Effect of specimen shape on creep response of a frozen sand : Ladanyi, B; Arteau, J Proc 1st International Symposium on Ground Freezing, Bochum, 8–10 March 1978, P141–153. Publ: Bochum, Ruhr University, 1978

Propagations of the Surface Fatigue Cracks in Various Kinds of Notched Specimens

In this report, the crack propagations in several kinds of notched round bar specimens of SK 5 and SUS 50 steels are investigated. The main results are summarized as follows. (1) It is possible to estimate the S-N curves for any notched specimen by using the idea of ε0, which has been often adopted to predict the endurance limit for crack initiation. (2) If the same crack length is obtained for the imposition of the same number of cycles, the crack propagation rates coincide with each other irrespective of the notch root radius and the materials. (3) In opposition to the results in (2), the effect of specimen shape appears on the crack propagation in the radial direction. (4) The index "m" for the formula dl/dN=CKm or dl/dN=Cσm1n, is considered to be related with the gradient of S-N curve and varies from 4 to 5 depending on the stress amplitude.

Stress Distribution under Uniaxal Elastic Plane Strain Compression with Friction

The elastic compression of a block with Coulomb friction on the tool-specimen interface is analysed, where the total stiffness matrix is rearranged according to the condition for nodes on frictional plane in Finite Element Method. As an example, the distribution of stresses in a block, the area of sticking on the contact surface, the distribution of displacement in the block, the pressure distribution and the mean pressure on the contact surface are calculated under plane strain condition. The effects of specimen shape, friction coefficient and Poisson's ratio on the calculated results are studied. The area of sticking on the contact surface increases with a decrease in block height, with an increase in friction coefficient and with a decrease in Poisson's ratio. The thinner the block is, the higher the pressure which is necessary for yielding becomes. Discussions are made on the calculated results as well as on the property of unsymmetric stiffness matrix in the analysis.

Effect of specimen shape and dimension on elongation of tensile test pieces of 6061 and 7075 alloy sheets

Effects of specimen dimensions on elongation at tensile tests were studied for aluminum alloy sheets, 3.8mm thick 6061-T6 alloy and 6.2mm thick 7075-T6 alloy. The optimum size and shape of tensile specimens were discussed, based on the present and the previous studies. The principal results obtained are as follows:(1) From the longitudinal strain distribution of the specimens, various alloys can be classified into three group; (a) Barba type, (b) Oliver type and (c) modied Barba type.(2) The percentage elongation of materials of the Barba type is reasonably constant when the ratio of the gage length to the square root of the cross sectional area L0/√A is kept constant.(3) Even when L0/√A is constant, the percentage elongation of the Oliver type specimens increasess slightly as the ratio of the reduced section length to the specimen width, Lc/W, incrases. Lc/W, not less than 5.5, is desirable for this type of materials.(4) Some modified Barba type specimens shows the Lc/W dependence of the percentage elongation, similar to that exhibited by the Oliver type.(5) The length of the necked region can be measured from the strain distribution in the Barba and the modified Barba type materials. It was shorter than 5√A for most materials. Thus, the gage length should be larger than 5√A.(6) The shoulder region, lf costraining the strain distribution, is 0.2-0.4 times W when W/T>4. In order to eliminate the effect of the shoulder on the elongation, Lc should be larger than L0+0.8 W. lf/W increases as W/T decreases and nearly equals to 1 in the square cross sectioned specimens. Thus, when W/T is nearly equal to 1, Lc should be taken as L0+2W.

Microwave Measurement of Saturation Magnetization of Ferrites

A microwave method of measurement of 4πMs, for high-resistivity materials such as ferrites and garnets is described. The method employs the ferromagnetic resonance absorption of microwave energy, and the shape-dependent demagnetization effects as given by Kittel's equation to evaluate 4πMs. Effects of specimen shape and position are analyzed, and the superiority of a method employing two pieces in the waveguide is pointed out. The advantages of these techniques over the usual magnetometer methods are compatibility with measurements on other parameters, ease of shaping the specimen, avoidance of calibration procedures and simplicity of setup. In particular, this method is the most convenient for ferrite thin films.

19—A STUDY OF NEEDLED FABRICS PART I: EXPERIMENTAL METHODS AND PROPERTIES

Methods of producing a fibre web for needle-punching on a laboratory machine are described: a parallel-laid card web was suitable for most purposes, though a cross-laid web was less anisotropic. Methods of operation and testing are described; the effects of specimen shape and size on tensile-test results were studied. The effects of web weight and structure were investigated, and experimental results are given: heavier-weight fabrics show much greater consolidation on needling.

Regarding the effect of specimen shape on the selection of the primary slip plane

Regarding the effect of specimen shape on the selection of the primary slip plane

Network characterization of silicone rubber vulcanizates. Part I. solvent, temperature, and specimen shape effects on effective crosslink density determinations

AbstractThe effective crosslink densities were determined for four silica‐filled silicone rubber vulcanizates which represent different degrees of crosslinking. The determinations were made from compression‐deflection measurements of rubber specimens at an equilibrium swelling condition. Nine solvents representing a wide range of dilatant strengths were investigated at four equilibrium temperatures (8, 23, 41, and 60°C.) for their effect on the crosslinking determinations. Specimen shape effects were also investigated. Explicit equations of state were derived empirically and were found to be similar to the well‐known Mooney‐Rivlin equation in which two independent parameters are required for the definition of a dilated rubber network.

Plasma Resonance in Crystals: Observations and Theory

Observations are reported of an electron plasma resonance absorption line in a magnetic field in an $n$-type crystal of InSb at 9000 and 24 000 Mc/sec and at 4\ifmmode^\circ\else\textdegree\fi{} and 77\ifmmode^\circ\else\textdegree\fi{}K. The magnitude of the plasma frequency and its dependence on rf frequency and on the orientation of the figure axis of the specimen relative to the static magnetic field are in approximate agreement with the elementary theory of the plasma resonance developed previously by the authors. The line shape is discussed for experiments carried out under conditions of carrier modulation and magnetic field modulation. A theoretical discussion is given of the effects of specimen shape and of the possibility of detection of minority carrier cyclotron resonance in the presence of a majority carrier plasma. Eddy current effects are discussed, with reference to the possibility of the detection of cyclotron resonance in metals and semimetals.