Dynamic strain aging

Strain aging can also occur in susceptible steels by welding near a crack, causing embrittlement (called dynamic strain aging). For this and other reasons, many users require that plate material intended for pressure-containing components be scanned by ultrasonic inspection equipment for cracks and flaws near edges to be welded. 

Although Y ions present only weak obstacles to dislocation motion [58], they are present in high concentrations and could, in theory, yield a large contribution to the flow stress. However, the crystals presently available apparently contain very small precipitates of ZrN [71] which provide stronger obstacles to slip than do unassociated Y ions [58, 72, 73]. Nonetheless, these unassociated Y ions do cause plastic instabilities, such as dynamic strain aging or the Portevin-Le Chatelier effect in... 

Rack, H.J., Dynamic Strain Aging of Metastable Beta Titanium Alloys, Sen Metall.,Wo 9,1975, p. 829-831... 

Win73] Winstone, M.R., Rawlings, R.D., and West, D.R.F., Dynamic Strain Aging in Some Titanium-Silicon Alloys, J. 

This can be seen in Fig. 3.86 [85] for a 0.17 % C carbon steel. Monotonic ultimate strength temperature indicating that dynamic strain aging is taking place between 250 and 300 °C. 

Tests have been run to derive the cyclic stress-strain curve both at 25 °C and at the operating temperature of 288 °C. Results are shown in Fig. 6.43. It is possible to recognize that at 288 °C the material is undergoing a dynamic strain aging process that makes the steel behave much better than at room temperature. The Ramberg-Osgood Eq. (6.3) of the cyclic curve at 288 °C is... 

Cie] Mechanical tests Dynamic strain aging... 

The variation of relative abrasive wear resistance (RAWR) as a function of temperature for ductile iron is presented in Fig. 6.14a [74], It is clear that the abrasive wear resistance shows a maximum at around 323-373 K. The RAWR is 20% lower at higher temperature than at ambient temperature. The high value of the RAWR at around 323-373 K is attributed to dynamic strain ageing. In contrast, the decrease of RAWR with increase of temperature is related to loss of strength and ductility of the ductile iron at high temperature. 

It is observed that the values do not reach its initial position within the relaxation time of the experiment, but a recovery of the E values have been attained (Fig. 18). This behaviour of a rubber can be explained by the stress softening effect during the dynamic strain. Nevertheless, a high extent of recovery in the reverse amplitude sweep indicates that a good filler-filler network has been re-established at a low loading of tubes in the S-SBR-BR matrix. So, at least it can be said that rather than damage or permanent break of the tubes, the amplitude sweep disrupted the filler-filler network in the rubber matrix. It is noted that the absolute values of E at small amplitudes are somewhat differed from each other as compared with the value obtained from the phr CNT-filled compound. The difference may be developed from ageing of the samples. 

The plastic strain at fracture decreases markedly with time as the cement ages also the elastic modulus increases (Wilson, Paddon Crisp, 1979 Barton et al., 1975). There is an increase in dynamic modulus with time (Barton et al., 1975). 

Fig. 22 Steady state incoherent intermediate scattering functions (z) measured in the vorticity direction as functions of accumulated strain jf for various shear rates y data from molecular dynamics simulations of a supercooled binary Lenard-Jones mixture below the glass transition ate taken from [91]. These collapse onto a yield scaling function at long times. The wavevector is q = 3.55/R (at the peak of Sq). The quiescent curve, shifted to agree with that at the highest y, shows ageing dynamics at longer times outside the plotted window. The apparent yielding master function from simulation is compared to those calculated in ISHSM for glassy states at or close to the transition (separation parameters s as labeled) and at nearby wave vectors (as labeled). ISHSM curves were chosen to match the plateau value fq, while strain parameters yc = 0.083 at = 0 solid line) and y, = 0.116 at e = 10 dashed line) were used from [45]...

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