Effect of Friction and Specimen Geometry on the Ductile Fracture in Upset Forging

1975 ◽  
Vol 97 (1) ◽  
pp. 14-20 ◽  
Author(s):  
S. K. Samanta
Keyword(s):  
Surface Stress ◽  
Room Temperature ◽  
Specimen Geometry ◽  
Circular Cylinders ◽  
Surface Cracks ◽  
Interface Friction ◽  
Flow Limit ◽  
Stress Components ◽  
Upset Forging ◽  
Ductile Flow

Experiments were conducted to determine the effect of interface friction and specimen geometry on the useful ductile flow limit of 1100 aluminum and 1095 steel at room temperature. The tests consisted of measuring the equatorial strains during simple upsetting of circular cylinders. From the measured strains the surface stress components were calculated. All occurrences of fracture were observed to be the normal type. In some cases no surface cracks were observed and a possible explanation is given in the paper.

Influence of Pressure Amplitude on Formability in Pulsating Hydro-Bugling of AZ31B Magnesium Alloy Sheet

2011 ◽  
Vol 128-129 ◽  
pp. 397-402
Author(s):  
Lian Fa Yang ◽  
Liang Yi ◽  
Chen Guo
Keyword(s):  
Magnesium Alloy ◽  
Wall Thickness ◽  
Room Temperature ◽  
Alloy Sheet ◽  
Pressure Amplitude ◽  
Excellent Performance ◽  
Az31b Magnesium Alloy ◽  
Stress Components ◽  
Uniform Expansion ◽  
Az31b Magnesium Alloy Sheet

The formability of the magnesium alloy sheets is poor at room temperature even though the magnesium alloy sheets are attractive because of their excellent characteristics. Application of pulsating hydroforming is a new and effective method to improve the formability. The effects of the pressure amplitude on the maximum bulging height and minimum wall thickness of the formed parts of AZ31B magnesium alloy sheets are examined using finite element simulations. It is shown that the distribution of maximum bugling height and minimum wall thickness is similar for different pressure amplitude A, and a uniform expansion in bulging region is obtained, the cause of the uniform expansion obtained may be caused by the variation of stress components. The AZ31B sheet has an excellent performance in formability when the pressure amplitude and pulsating frequency are properly selected.

The Effect of Flash Freezing on Variability in Spinal Cord Compression Behavior

2009 ◽  
Vol 131 (11) ◽  
Author(s):  
Carolyn J. Sparrey ◽  
Tony M. Keaveny
Keyword(s):  
Spinal Cord ◽  
Mechanical Behavior ◽  
Mechanical Response ◽  
Peak Stress ◽  
Specimen Geometry ◽  
Specimen Preparation ◽  
Spinal Cord Tissue ◽  
Compression Behavior ◽  
Interface Friction ◽  
Cord Injury

The compression behavior of spinal cord tissue is important for understanding spinal cord injury mechanics but has not yet been established. Characterizing compression behavior assumes precise specimen geometry; however, preparing test specimens of spinal cord tissue is complicated by the extreme compliance of the tissue. The objectives of this study were to determine the effect of flash freezing on both specimen preparation and mechanical response and to quantify the effect of small deviations in specimen geometry on mechanical behavior. Specimens of porcine spinal cord white matter were harvested immediately following sacrifice. The tissue was divided into two groups: partially frozen specimens were flash frozen (60 s at −80°C) prior to cutting, while fresh specimens were kept at room temperature. Specimens were tested in unconfined compression at strain rates of 0.05 s−1 and 5.0 s−1 to 40% strain. Parametric finite element analyses were used to investigate the effect of specimen face angle, cross section, and interface friction on the mechanical response. Flash freezing did not affect the mean mechanical behavior of the tissue but did reduce the variability in the response across specimens (p<0.05). Freezing also reduced variability in the specimen geometry. Variations in specimen face angle (0–10 deg) resulted in a 34% coefficient of variation and a 60% underestimation of peak stress. The effect of geometry on variation and error was greater than that of interface friction. Taken together, these findings demonstrate the advantages of flash freezing in biomechanical studies of spine cord tissue.

scholarly journals The influence of surface effects in the problem of theory of elasticity for a circular hole in a half-plane

2020 ◽  
pp. 250-259
Author(s):  
D. V Gandilyan
Keyword(s):  
Fourier Series ◽  
Stress Concentration ◽  
Half Plane ◽  
Surface Stress ◽  
Surface Elasticity ◽  
Surface Effects ◽  
Theory Of Elasticity ◽  
Plane Boundary ◽  
Problem Solution ◽  
Stress Components

Surface effects are important for modeling structures, such as nanofilms, nanoporous materials, and other nanoscale constructions. In the current study, we consider the problem of the theory of elasticity - the problem of a half-plane containing a circular hole, stretched by constant stresses applied at infinity, and take into account surface effects such as surface elasticity and surface stresses. The problem solution has been obtained by expanding the Fourier series with the variables written in the bipolar coordinate system (which simplifies the problem solution because one of the coordinates becomes a constant on the hole contour), where the stress components are expressed through a bi-harmonic stress function. The parametric coefficients involved in the solution, namely in the Fourier series, are determined in order to satisfy the boundary conditions on the hole contour. To solve the problem, in addition to the equations of the theory of elasticity, the equations of surface elasticity were used, in particular, by applying the generalized Young-Laplace’s law and the Shuttleworth’s law; the surface stress on the hole contour has been calculated directly. Using recurrence relations for the stress components at the boundary, stress concentration values have been obtained. The resulting expressions can be considered as a generalized solution of the problem in case of the classical elasticity. The stress concentrations are compared for the cases with and without taking into account surface effects at various points on the hole contour. The contribution caused by the surface effects depending on the relative distance between the hole and the half-plane boundary is studied. It is shown that despite a quite simple geometry, owing to the fairly small distance between the hole and the half-plane boundary, the stress concentration with and without taking into account the surface stress are significantly different from each other, due to the significant contribution of surface effects.

scholarly journals Strengthening and Thermally Activated Processes in an AX61/Saffil Metal Matrix Composite

Crystals ◽  
2020 ◽  
Vol 10 (6) ◽  
pp. 466
Author(s):  
Zuzanka Trojanová ◽  
Zoltán Száraz ◽  
Pavel Lukáč ◽  
Zdeněk Drozd ◽  
Ján Džugan
Keyword(s):  
Metal Matrix ◽  
Room Temperature ◽  
Load Transfer ◽  
Strengthening Mechanisms ◽  
Thermally Activated ◽  
Squeeze Cast ◽  
Stress Components ◽  
Activated Processes ◽  
Relaxation Curves ◽  
Thermally Activated Process

AX61 magnesium alloy was reinforced with short Saffil fibres using squeeze cast technology. Samples were cut from the casting in two directions: parallel and perpendicular to the fibre plane. Samples were deformed in compression at various temperatures from room temperature to 300 °C. Various strengthening mechanisms such as load transfer, increased dislocation density, Orowan and Hall–Petch strengthening were analysed. During deformation, the stress relaxation tests were subsequently performed. The relaxation curves were evaluated with respect to Li and Feltham equations with the aim to find stress components in matrix and parameters of the thermally activated process(es).

Site-Specific Evolution of Surface Stress during the Room-Temperature Oxidation of theSi(111)−(7×7)Surface

2010 ◽  
Vol 104 (14) ◽  
Author(s):  
N. T. Kinahan ◽  
D. E. Meehan ◽  
T. Narushima ◽  
S. Sachert ◽  
J. J. Boland ◽  
...  
Keyword(s):  
Surface Stress ◽  
Room Temperature ◽  
Temperature Oxidation ◽  
Site Specific

Improvement in mechanical properties of sintered zirconia (3% yttria stabilized) by glass infiltration

2007 ◽  
Vol 22 (9) ◽  
pp. 2550-2557 ◽  
Author(s):  
A. Balakrishnan ◽  
B.B. Panigrahi ◽  
Min-Cheol Chu ◽  
T.N. Kim ◽  
Kyung-Jin Yoon ◽  
...  
Keyword(s):  
Surface Stress ◽  
Thermal Shock Resistance ◽  
Room Temperature ◽  
Significant Contribution ◽  
Elastic Stress ◽  
Treated Sample ◽  
Drastic Increase ◽  
Shock Resistance ◽  
Strength Increment ◽  
Room Temperature Strength

The goal of this work was to improve the strength of sintered zirconia (3 mol% yttria stabilized) by surface treatment, using a low expansion glass (Mg3Al2Si6O18) at high temperature. The room-temperature strength was increased by about 42% when the glass was penetrated for 30 min. There was a drastic increase in the Weibull modulus. However, the longer holding time led to grain coarsening and the excess glass deteriorated the strength. The magnitude of the strength increment was on the order of surface stress measured experimentally and thermo-elastic stress predicted theoretically. A significant contribution of phase transformation of zirconia from tetragonal to monoclinic phase on the residual stress was also found. Furthermore, compared to the as-sintered zirconia, the glass-treated sample (penetrated for 30 min) exhibited relatively higher strength at elevated temperature (750 °C) and also showed a significant improvement in the thermal shock resistance behavior.

Study on Compression Behaviour of AZ31 Magnesium Alloy at Room-Temperature

2012 ◽  
Vol 476-478 ◽  
pp. 1960-1964
Author(s):  
Jia Le Sun ◽  
Rui Chun Li ◽  
Gao Feng Quan ◽  
Zhao Ming Liu
Keyword(s):  
Magnesium Alloy ◽  
Strain Hardening ◽  
Room Temperature ◽  
Deformation Behaviour ◽  
Az31 Alloy ◽  
Strain Hardening Exponent ◽  
Surface Cracks ◽  
Compression Properties ◽  
Compression Behaviour ◽  
Az31 Mg Alloy

The microstructure, surface morphology, compression properties, deformation behaviour and strain hardening exponent of as-cast and as-extruded AZ31 Mg alloy after different annealing treatments were investigated. The results show that the compression properties are great different between cast AZ31 alloy and extruded AZ31 alloy. Extruded AZ31 alloy is discontinuous yield and on the surface no signs of damage have been observed; on the contrast, cast AZ31 alloy is continuous yield and shows wavy patterns, and the surface cracks can be easily found. In addition, there is a linear relationship between the strain hardening exponent in first deformation stage and the yield ratio. Further more, the twinning mechanism plays very different role in cast AZ31 alloy and extruded AZ31 alloy.

Effect of Healing Temperature on Crack-Healing of Al2O3 Toughened by SiC Particles

2010 ◽  
Vol 650 ◽  
pp. 109-114 ◽  
Author(s):  
Chun Yan Shi ◽  
Ying Kui Guo ◽  
Shu Jin Zhao ◽  
Chun Mei Song
Keyword(s):  
Reaction Mechanism ◽  
Oxidation Reaction ◽  
Room Temperature ◽  
Adsorption Mechanism ◽  
Bending Strength ◽  
Surface Cracks ◽  
Crack Healing ◽  
Hot Press ◽  
Sic Particles ◽  
Healing Temperature

Al2O3 Toughened by SiC particles was hot-press sintered. Cracks of ~300μm in diameter were introduced in the surfaces of specimens, which then healed at 1000°C, 1200°C, 1300°C, 1400°C, and individually for 2h, 4h, 6h and 8h. Effect of healing temperature on bending strength, healing mechanism were systematically investigated, the results show that the best bending strength recovered at room temperature was 583.61MPa obtained at 1300°C for 4h, which was the same value as perfect specimens. The recovery of bending strength contributes to three kinds of mechanisms. When specimens were healed individually at 1000°C, 1200°C, 1300°C for 2h, adsorption mechanism and proliferation mechanism were as the dominant healing mechanisms; when healed at 1400°C for 2h, oxidation reaction mechanism was the important healing mechanism. Also, the length of surface cracks is shorter as healing temperature increasing.

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