The damage evolution in Bi2223 filaments and its influence on critical current was described by a Monte Carlo-shear lag simulation method. The experimentally observed zigzag crack propagation across aligned Bi2223 grains under tensile strain was effectively modelled by including transverse and longitudinal failure modes for individual grains. From the simulated stress-strain curve, the survival parameter (slope of the stress-strain curve normalized with respect to the original Young's modulus) was estimated with increasing applied strain. With this parameter combined with the strain sensitivity of the critical current, the measured change of critical current of the composite tape with applied strain could be described well.
The distribution of the local critical current and the n-value along the sample length and its relation to the overall critical current were studied experimentally and analytically for the bent multifilamentary Bi2223/Ag/Ag-Mg alloy superconducting composite tape. Then, based on the results, it was attempted to simulate on a computer the dependence of the critical current on the sample length. The main results are summarized as follows. The experimentally observed relation of the distributed local critical current and n-value to the overall critical current was described comprehensively with a simple voltage summation model, in which the sample was regarded as a one-dimensional series circuit. The sample length dependence of the critical current was reproduced on the computer by a Monte Carlo simulation incorporating the voltage summation model and the regression analysis results for the local critical current distribution and the relation of the n-value to the critical current.
The process of damage extension under bending and tensile strains at room temperature and its influence on critical current at 77 K under zero magnetic field were studied for a mutifilamentary Bi2223/Ag/Ag_ Mg alloy superconducting composite tape. Under the tensile strain, the damages such as transverse cracking of the Bi2223 filaments, longitudinal cracking along the fila ment axis and interfacial debonding between Bi2223 and Ag took place. Under the bending strain, in addition to these damages, protrusion of the compressive side due to buckling, accompanied by compressive fracture of the filaments, was observed. From the analysis of the residual stress, tensile stress_ strain curve and tensile damage_ induced reduction in critical current, the Young's modulus, residual strain and intrinsic tensile fracture strain of the Bi2223 filaments at room temperature were estimated to be 98 GPa, |0.16÷ and 0.09`0.13÷, respectively. The change of critical current with bending strain was calculated by sub stituting these estimated values and compressive strength of the filaments as a variable into the proposed model in which the in fluence of the damages both in tensile and compressive sides on critical current was incorporated. From the comparison of the cal culation and experimental results, the compressive strength of Bi2223 filaments was estimated to be several times higher than the tensile one.
Bending behavior of Bi2223/Ag superconducting composite tapes, and the influence of the bending damages on critical superconducting current Ic and n-value that is a measure for the sharpness of the transition from super- to normal conduction, were studied. Following damages, responsible to the reduction in critical current at high bending strains, were observed. (i) Transverse and (ii) longitudinal crackings of the filaments, (iii) interfacial debonding between filaments and silver, and (iv) buckling in compression side. The damage of the filaments arose first locally, resulting in a reduction of the Ic and n-value in the corresponding local portion. The overall Ic and n-values were determined by such a local portion. With increasing strain, the damage of the other portions arose successively, resulting in loss of superconductivity in all portions.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.