Investigation of the mechanical properties of Bi-2223 superconducting tapes was performed by tensile tests. The results show rapid degradation of the critical current after exceeding 0.4% strain. The shape of the I_c = f() curves and the so-called irreversible strain remain identical for various magnetic fields (0-8 T) and temperatures (4.2, 20, 77 K), demonstrating independence of the mechanical properties from these parameters. The superconducting tapes were treated as a composite consisting of a plastic matrix with brittle ceramic fibres. Under uniform tensile load, the probability of the filament fracture follows a Weibull distribution. Its inverse function, the probability of the number of unbroken filaments, is compared with the relative degradation of the critical current obtained from experiment.