Incident Wave and Dislocation Acceleration Effects in Dislocation Emission From Cracks

1990 ◽  
Vol 57 (4) ◽  
pp. 870-876 ◽  
Author(s):  
L. M. Brock ◽  
J.-S. Wu
Keyword(s):  
Exact Solution ◽  
Yield Stress ◽  
Stress Level ◽  
Equation Of Motion ◽  
Dislocation Emission ◽  
Sinusoidal Wave ◽  
Sh Wave ◽  
Wave Parameters ◽  
Subcritical Speed ◽  
Plane Sh Wave

Some previous transient analyses of dislocation emission from dynamically loaded cracks have treated glide at constant speeds, and have invoked an emissions criterion that allows the dislocation force to exceed the yield stress level during glide. In the context of nonstrain-hardening plasticity, this analysis requires that the force remain at the yield stress level. For an exact solution to the problem of screw dislocation emission from a crack subjected to plane SH-wave diffraction, the result is an equation of motion for the dislocation, which can be integrated exactly. The dislocation is found to accelerate during glide to a high but subcritical speed, before decelerating to its arrest position. A general incident SH-wave is considered, but is then specialized to the cases of a step-stress and a sinusoidal wave. Calculations on the basis of material and wave parameters show that purely brittle fracture can be difficult to achieve, and that wavelength/frequency cutoffs exist, beyond which emission cannot occur.

A series exact solution for one-dimensional non-linear particle equation of motion

2011 ◽  
Vol 207 (1-3) ◽  
pp. 461-464 ◽  
Author(s):  
M. Jalaal ◽  
H. Bararnia ◽  
G. Domairry
Keyword(s):  
Exact Solution ◽  
Equation Of Motion ◽  
One Dimensional ◽  
Non Linear

Scattering of Anti-Plane SH-Wave by the Semi-Cylindrical Gap with Multiple Shallow-Buried Inclusions in Elastic Semi-Space

2012 ◽  
Vol 569 ◽  
pp. 78-81
Author(s):  
Hong Liang Li ◽  
Jing Guo ◽  
Li Ming Cai
Keyword(s):  
Displacement Field ◽  
Ground Surface ◽  
Analytic Solutions ◽  
Polar Coordinate System ◽  
Algebraic Equations ◽  
Sh Wave ◽  
Dynamic Stress Concentration Factor ◽  
Polar Coordinate ◽  
Cylindrical Inclusions ◽  
Plane Sh Wave

Semi-cylindrical gap and Multiple circular inclusions exists widely in natural media, composite materials and modern municipal construction. The scattering field produced by semi-cylindrical gap and multiple circular inclusions determines the dynamic stress concentration factor around the gap and circular inclusions, and therefore determines whether the material is damaged or not. These problems are complicated. It is hard to obtain analytic solutions except for several simple conditions. In this paper, the solution of displacement field for elastic semi-space with semi-cylindrical gap and multiple cylindrical inclusions by anti-plane SH-wave is constructed. In complex plane, considering the symmetry of SH-wave scattering , the displacement field aroused by the anti-plane SH-wave and the scattering displacement field impacted by the gap and the cylindrical inclusions comprised of Fourier-Bessel series with undetermined coefficients which satisfies the stress-free condition on the ground surface are constructed. Through applying the method of multi-polar coordinate system, the equations with unknown coefficients can be obtained by using the displacement and stress condition around the edge of the gap and cylindrical inclusions. According to orthogonality condition for trigonometric function, these equations can be reduced to a series of algebraic equations. Then the value of the unknown coefficients can be obtained by solving these algebraic equations. The total wave displacement field is the superposition of the displacement field aroused by the anti-plane SH-wave and the scattering displacement field. By using the expressions, an example is provided to show the effect of the change of relative location of the cylindrical inclusions.

Early Fatigue Damage of Magnesium Alloy On-Line Monitoring by Nonlinear Ultrasonic

2010 ◽  
Vol 139-141 ◽  
pp. 194-197
Author(s):  
Bing Sheng Yan ◽  
Bin Wu ◽  
Cun Fu He ◽  
Jing Pin Jiao
Keyword(s):  
Fatigue Life ◽  
Magnesium Alloy ◽  
Yield Stress ◽  
Fatigue Damage ◽  
Stress Level ◽  
Second Harmonic ◽  
Experimental Results ◽  
Nonlinearity Parameter ◽  
Acoustic Nonlinearity Parameter ◽  
On Line

This research develops a robust experimental procedure to monitor the evolution of early fatigue damage in AZ31 magnesium alloy with the acoustic nonlinearity parameter , and demons- trats its reliability by measuring the linear relationship between amplitudes of the second-harmonic waves and fundamental waves squared. Using this system, of two sets of specimens with different stress level is measured. The experimental results show that there is a significant increase in linked to fatigue degree in the early stages of fatigue life and reaches the maximum about 55%of fatigue life, when the stress level is ±60%of the yield stress, can characterize the early fatigue damage of magnesium alloy. However, when the stress level is ±70%of the yield stress, there is a regular fluctuation in linked to fatigue degree, this experimental results can’t be explained.

WEHRL ENTROPY AND ENTANGLEMENT OF A TIME-DEPENDENT TWO-LEVEL TRAPPED ION INTERACTING WITH A LASER FIELD

2008 ◽  
Vol 06 (02) ◽  
pp. 331-339
Author(s):  
MAHMOUD ABDEL-ATY ◽  
SAYED ABDEL-KHALEK ◽  
ABDEL-SHAFY F. OBADA
Keyword(s):  
Exact Solution ◽  
Time Evolution ◽  
Laser Field ◽  
Equation Of Motion ◽  
Time Dependent ◽  
Heisenberg Equation ◽  
Wehrl Entropy ◽  
Entanglement Generation ◽  
Trapped Ion ◽  
Cat States

The time evolution of the atomic Wehrl entropy and long-lived entanglement generation using a single trapped ion interacting with a laser field are analyzed. Starting from the Heisenberg equation of motion, an exact solution of the system is obtained by indicating that there are some interesting features when a time-dependent modulating function is considered. We demonstrate that the long-living quantum entanglement can be obtained using the time-independent interaction when the field is initially in a pair cat states.

scholarly journals Factors Influencing the Plane-Strain Crack Toughness Values of a Structural Steel

1969 ◽  
Vol 91 (3) ◽  
pp. 506-511 ◽  
Author(s):  
A. K. Shoemaker
Keyword(s):  
Strain Rate ◽  
Structural Steel ◽  
Yield Stress ◽  
Plane Strain ◽  
Stress Level ◽  
Room Temperature ◽  
Fatigue Cracking ◽  
Strain Rates ◽  
Fatigue Stress ◽  
Plane Strain Crack

An investigation was conducted to determine the effects of the variables; temperature, strain rate, and precracking fatigue-stress level, on plane-strain crack toughness values of a rate and temperature-sensitive steel. The crack toughness behavior of a 3/4-in-thick structural steel plate, which had a static room-temperature yield stress of 45,000 psi, was examined over the temperature range from −280 to 0 deg F for strain rates of 8 × 10−5/sec, 3 × 103/sec, and 1.5/sec. Crack toughness data, which were obtained from notched bend and single-edge-notched specimens, are presented for precracking conditions obtained at a maximum nominal fatigue stress of 25 percent and 50 percent of the room-temperature yield stress. The plane-strain crack toughness, KIc-values showed only a small sensitivity to changes in temperature and no effect due to changes in strain rate. The beginning of the transition from plane-strain to plane-stress conditions occurred at successive increases in temperature for increasing strain rate. The requirement of B > 2.5 × (KIc/σys)2 for plane-strain behavior of high-strength steels was also valid for this material when the yield stress was evaluated at the test temperature and strain rate. Increasing the fatigue-cracking stress level from 25 to 50 percent of the room-temperature nominal yield stress increased the apparent KIc-values. The data showed that a necessary condition for obtaining valid KIc-values is that the plastic-zone size which develops during fatigue cracking at room temperature must be less than that which occurs at the low temperatures and elevated strain rates of the KIc tests.

Sign in / Sign up

Export Citation Format

Share Document