Stress Concentrations for Filled and Unfilled Closely Spaced Cylindrical Defects

1985 ◽  
Vol 107 (4) ◽  
pp. 271-276 ◽  
Author(s):  
T. Ihara ◽  
M. C. Shaw
Keyword(s):  
Brittle Fracture ◽  
Tensile Stress ◽  
Young’S Modulus ◽  
Fracture Stress ◽  
Brittle Materials ◽  
Critical Value ◽  
Stress Concentrations ◽  
High Quality ◽  
Close Spacing ◽  
The Matrix

All real materials contain defects which significantly reduce the fracture stress of brittle materials. It has been proposed by Griffith [3] that brittle fracture occurs when the maximum intensified tensile stress on the surface of a defect reaches a critical value. It has recently been found [1] that for many brittle materials of high quality, the nature and density of the defects are such that they may be modelled by isolated cylindrical voids. This study considers the stress intensification consequences of the close spacing of cylindrical defects that are filled with a material having a Young’s modulus different than that of the matrix.

Segregation and the strength of grain boundaries

1976 ◽  
Vol 349 (1659) ◽  
pp. 535-554 ◽  
Keyword(s):  
Brittle Fracture ◽  
Grain Boundary ◽  
Fracture Stress ◽  
Temperature Shift ◽  
Solute Segregation ◽  
Incorrect Assumption ◽  
The Matrix ◽  
Steel Aisi ◽  
The Impact ◽  
Work Of Fracture

A quantitative theory is presented which explains how solute segregation alters grain boundary strength. A simple treatment shows that, because of an incorrect assumption, previous theories in which segregation was thought to cause low temperature brittleness by lowering the grain boundary work of fracture are incorrect and that it is the brittle fracture stress that is altered. The decrease in grain boundary brittle fracture stress is shown to be proportional to the level of segregation and also to the excess size of the segregant atoms over those of the matrix. From the tem­perature dependence of the yield stress in a given alloy, it is then simple to calculate the impact transition temperature shift caused by the segrega­tion of various species. An evaluation for the temper brittle steel, AISI 3340, gives a good numerical correlation with the published transi­tion temperature shifts for the segregation of P, Sn, Sb, As, Si, Ge and Bi. The theory also explains why C, B and Be are remedial to the embrittle­ment of pure iron.

Effect of temperature on matrix multicracking evolution of C/SiC fiber-reinforced ceramic-matrix composites

2020 ◽  
Vol 39 (1) ◽  
pp. 189-199
Author(s):  
Longbiao Li
Keyword(s):  
Strain Energy ◽  
Ceramic Matrix Composites ◽  
Critical Value ◽  
Matrix Cracking ◽  
Interface Debonding ◽  
Matrix Composites ◽  
Temperature Dependent ◽  
Damage State ◽  
The Matrix ◽  
Sic Composites

AbstractIn this paper, the temperature-dependent matrix multicracking evolution of carbon-fiber-reinforced silicon carbide ceramic-matrix composites (C/SiC CMCs) is investigated. The temperature-dependent composite microstress field is obtained by combining the shear-lag model and temperature-dependent material properties and damage models. The critical matrix strain energy criterion assumes that the strain energy in the matrix has a critical value. With increasing applied stress, when the matrix strain energy is higher than the critical value, more matrix cracks and interface debonding occur to dissipate the additional energy. Based on the composite damage state, the temperature-dependent matrix strain energy and its critical value are obtained. The relationships among applied stress, matrix cracking state, interface damage state, and environmental temperature are established. The effects of interfacial properties, material properties, and environmental temperature on temperature-dependent matrix multiple fracture evolution of C/SiC composites are analyzed. The experimental evolution of matrix multiple fracture and fraction of the interface debonding of C/SiC composites at elevated temperatures are predicted. When the interface shear stress increases, the debonding resistance at the interface increases, leading to the decrease of the debonding fraction at the interface, and the stress transfer capacity between the fiber and the matrix increases, leading to the higher first matrix cracking stress, saturation matrix cracking stress, and saturation matrix cracking density.

The Mechanics of Ozone Cracking

1962 ◽  
Vol 35 (1) ◽  
pp. 200-209 ◽  
Author(s):  
M. Braden ◽  
A. N. Gent
Keyword(s):  
Tensile Stress ◽  
Crack Growth ◽  
Energy Requirement ◽  
Critical Energy ◽  
Critical Value ◽  
Experimental Measurements ◽  
Rubber Sheet ◽  
Polymer Molecules ◽  
Two Factors ◽  
Applied Tensile Stress

Abstract Experimental measurements are described of the growth of a cut in a stretched rubber sheet under the action of an atmosphere containing ozone. A well-defined rate of crack growth is obtained, substantially independent of the applied tensile stress when this exceeds a critical value necessary for growth to occur at all. The rate of growth is found to be similar for a number of polymers and principally determined by the ozone concentration when the mobility of the polymer molecules is sufficiently high. When the molecular mobility is inadequate, crack growth is retarded. The critical condition is found to be similar for all the polymers examined, and largely independent of the conditions of exposure; it appears to reflect an energy requirement for growth of about 40 ergs/cm2 of newly-formed surface. The effect of the degree of vulcanization and the presence of additives, including antiozonants, on these two factors has also been examined. The dialkyl-p-phenylene diamines are found to confer protection by raising the critical energy required for growth to occur, in contrast to other protective agents which affect only the rate of crack propagation.

scholarly journals The Thin Ice Layer Brittle Fracture Stress Model and de-icing Angle Optimization

2015 ◽  
Vol 121 ◽  
pp. 1296-1303 ◽  
Author(s):  
Chenghu Zhang ◽  
Jiyou Lin ◽  
Pengfei Chen ◽  
Yan Fu
Keyword(s):  
Brittle Fracture ◽  
Fracture Stress ◽  
Stress Model

Analysis of the Crack Fracture Morphology of the Asphalt Mixture under Tensile Stress Effects

2011 ◽  
Vol 250-253 ◽  
pp. 3533-3537 ◽  
Author(s):  
Li Hua Zhao ◽  
Jing Yun Chen ◽  
Sheng Wu Wang
Keyword(s):  
Brittle Fracture ◽  
Fracture Surface ◽  
Tensile Stress ◽  
Mechanical Characteristics ◽  
Asphalt Mixture ◽  
Fracture Morphology ◽  
Microscopic Mechanism ◽  
Interface Zone ◽  
Stress Effects ◽  
Bending Fracture

Through studying the bending fracture and cleavage fracture of the asphalt mixture within the different temperature condition, confirming that the temperature influences the microscopic mechanism of mixture cracking: the fracture is relatively flat with low temperture, the destruction of the asphalt mixture is also mainly result of the brittle fracture; As the temperature rise, fracture surface becomes coarse, some part show large plastic elapse deformation. Adding fiber can reduce thickness of the asphalt membrane, improve the bonding strength of asphalt mastic, and greatly increase the ratio of the aggregate fracture and interface zone fracture, so as to enhance the asphalt mixture crack-resistance. The fracture morphology of asphalt mixture has a better reflection for its mechanical characteristics.

Multi-Parameter Optimization to Improve the Erosion Resistance of Coating by Fe Simulation

2021 ◽  
Author(s):  
Fang Li ◽  
Liuxi Cai ◽  
Shun-sen Wang ◽  
Zhenping Feng
Keyword(s):  
Tensile Stress ◽  
Young’S Modulus ◽  
Impact Velocity ◽  
Coating Thickness ◽  
Poisson’S Ratio ◽  
Erosion Resistance ◽  
Young's Modulus ◽  
Tio2 Coating ◽  
Poisson's Ratio ◽  
Stress Peak

Abstract Finite element method (FEM) was used to study the stress peak of stress S11 (Radial stress component in X-axis) on the steam turbine blade surface of four typical erosion-resistant coatings (Fe2B, CrN, Cr3C2-NiCr and Al2O3-13%TiO2). The effect of four parameters, such as impact velocity, coating thickness, Young's modulus and Poisson's ratio on the stress peak of stress S11 were analyzed. Results show that: the position of tensile stress peak and compressive stress peak of stress S11 are far away from the impact center point with the increase of impact velocity. When coating thickness is equal to or greater than 10μm, the magnitude of tensile stress peak of stress S11 on the four coating surfaces does not change with the coating thickness at different impact velocities. When coating thickness is equal to or greater than 2μm, the magnitude of tensile stress peak of stress S11 of four coatings show a trend of increasing first and then decreasing with the increase of Young's modulus. Meanwhile, the larger the Poisson's ratio, the smaller the tensile stress peak of stress S11. After optimization, When coating thickness is 2μm, Poisson's ratio is 0.35 and Young's modulus is 800 GPa, the Fe2B coating has the strongest erosion resistance under the same impact conditions, followed by Cr3C2-NiCr, CrN, and the Al2O3- 13%TiO2 coating, Al2O3-13%TiO2 coating has the worst erosion resistance.

Significant reduction in Young's modulus of Fe–Ga alloy single crystal by inverse magnetostrictive effect under tensile stress

2018 ◽  
Vol 124 (23) ◽  
pp. 233901 ◽  
Author(s):  
S. Fujieda ◽  
S. Asano ◽  
S. Hashi ◽  
K. Ishiyama ◽  
T. Fukuda ◽  
...  
Keyword(s):  
Tensile Stress ◽  
Single Crystal ◽  
Young’S Modulus ◽  
Young's Modulus ◽  
Alloy Single Crystal

scholarly journals Afforestation of Former Farmland with High-value Hardwoods

1991 ◽  
Vol 67 (3) ◽  
pp. 209-212 ◽  
Author(s):  
F. W. von Althen
Keyword(s):  
Early Years ◽  
Intensive Management ◽  
High Quality ◽  
Close Spacing ◽  
Hardwood Species ◽  
Competition Control ◽  
Stem Development ◽  
Gradual Release ◽  
Poor Drainage

For satisfactory growth, most high-value hardwood species demand a deep, fertile, moist but well drained soil. Intensive competition control during the early years after planting is a necessity. Close spacing is recommended, with gradual release of crop trees to promote high-quality stem development. For good hardwood growth on soils of marginal fertility or poor drainage or on sites where intensive management cannot be guaranteed, it is recommended that a mixture of several hardwood species be planted.

Principle of Strength Reinforcement in Filled Rubbers

1967 ◽  
Vol 40 (5) ◽  
pp. 1337-1363 ◽  
Author(s):  
A. E. Oberth
Keyword(s):  
Particle Size ◽  
Crosslink Density ◽  
High Modulus ◽  
Stress Concentrations ◽  
Volume Increase ◽  
The Matrix ◽  
Filled Rubbers ◽  
Filler Particles ◽  
Tear Properties ◽  
Properties Of Composites

Abstract Effects of filler on mechanical properties of composites result from stress concentrations developed in the matrix and filler particles. Stress concentrations in filler particles relieve stress in the matrix which, under a given load, deforms less than it would in absence of filler. This accounts for high modulus as well as strength reinforcement in filled materials. Stress concentration in the matrix, decreasing with increasing content of filler, is responsible for internal tearing of composites. Magnitude of this internal tearing, which can be measured by volume increase of a specimen under strain, depends on many factors such as: shape of filler, orientation of filler particles, particle size, particle size distribution, nature of boundary layer between filler and matrix, crosslink density and tear properties of the matrix, as well as environmental pressure in the test. High dilatation results in low tensile strength of the composite and conversely if dilatation is suppressed maximum strength reinforcement is obtained.

THE STUDY OF Pd SCHOTTKY CONTACT ON POROUS GaN FOR UV METAL–SEMICONDUCTOR–METAL (MSM) PHOTODETECTORS

2007 ◽  
Vol 16 (04) ◽  
pp. 497-503 ◽  
Author(s):  
L. S. CHUAH ◽  
Z. HASSAN ◽  
H. ABU HASSAN
Keyword(s):  
Molecular Beam Epitaxy ◽  
Tensile Stress ◽  
Molecular Beam ◽  
Schottky Contact ◽  
Nitrogen Plasma ◽  
Porous Sample ◽  
Optical Studies ◽  
High Quality ◽  
Metal Semiconductor Metal ◽  
Msm Photodetectors

High quality unintentionally doped n-type GaN layers were grown on Si (111) substrate using AlN (about 200 nm) as buffer layer by radio frequency (RF) nitrogen plasma-assisted molecular beam epitaxy (MBE). This paper presents the structural and optical studies of porous GaN sample compared to the corresponding as-grown GaN. Metal–semiconductor–metal (MSM) photodiode was fabricated on the samples. For as-grown GaN-based MSM, the detector shows a sharp cut-off wavelength at 362 nm, with a maximum responsivity of 0.254 A/W achieved at 360 nm. For porous GaN MSM detector, a sharp cut-off wavelength at 360 nm with a maximum responsivity of 0.655 A/W was achieved at 359 nm. Both the detectors show a little decrease in responsivity in the UV spectral region. The MSM photodiode based on porous GaN shows enhanced (2×) magnitude of responsivity relative to the as-grown GaN MSM photodiode. Enhancement of responsivity can be attributed to the relaxation of tensile stress and reduction of surface pit density in the porous sample.

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