Lifetime statistics for single Kevlar 49 filaments in creep-rupture

Experimental data are presented for the lifetime of single Kevlar 49 filaments under moderate to high stress levels at standard ambient conditions (21°C, 65% r.h.). Filaments were drawn from two spools, A and B, taken from the same production lot. Previously we found that filaments from spool A were 7% lower in mean strength but much less variable in diameter than filaments from spool B; however, the respective variabilities in failure stress were equivalent. The lifetime data were interpreted in light of a previously developed kinetic model embodying Weibull failure statistics and power law dependence of lifetime on stress level. As predicted, lifetime data at each stress level generally followed a two-parameter Weibull distribution with a shape parameter value near 0.2. Based on absolute stress levels, the filaments drawn from spool B had a Weibull scale parameter for lifetime about ten times greater than those from spool A; however, when the stress-levels were normalized by the respective Weibull scale parameters for short-term strength, these differences disappeared. With respect to power law dependence of lifetime on stress level, three distinct time domains emerged, each marked by a different power law exponent. Similar behaviour was observed earlier for preproduction Kevlar 49/epoxy strands, and the values for the power law exponents for the filaments agree closely with those for the strands.

[1]  Bernard D. Coleman,et al.  A Stochastic Process Model for Mechanical Breakdown , 1957 .

[2]  S. Leigh Phoenix,et al.  Stochastic strength and fatigue of fiber bundles , 1978, International Journal of Fracture.

[3]  Richard M. Christensen.  Interactive mechanical and chemical degradation in organic materials , 1984 .

[4]  R. J. Morgan,et al.  The relationship between the physical structure and the microscopic deformation and failure processes of poly(p-phenylene terephthalamide) fibers , 1983 .

[5]  D. Prevorsek,et al.  Fatigue Fracture in Fibrous Polymers as a Brittle, Crack-Nucleation Process , 1964 .

[6]  Peter Schwartz,et al.  A Study of Statistical Variability in the Strength of Single Aramid Filaments , 1984 .

[7]  W. Meeker,et al.  Weibull Variances and Confidence Limits by Maximum Likelihood for Singly Censored Data , 1977 .

[8]  Bernard D. Coleman,et al.  Time Dependence of Mechanical Breakdown Phenomena , 1956 .

[9]  B. D. Coleman.  Time Dependence of Mechanical Breakdown in Bundles of Fibers. III. The Power Law Breakdown Rule , 1958 .

[10]  R. Ericksen.  Creep of aromatic polyamide fibres , 1985 .

[11]  H. Eyring.  Viscosity, Plasticity, and Diffusion as Examples of Absolute Reaction Rates , 1936 .

[12]  S. L. Phoenix,et al.  STATISTICS FOR THE TIME DEPENDENT FAILURE OF KEVLAR-49/EPOXY COMPOSITES: MICROMECHANICAL MODELING AND DATA INTERPRETATION , 1983 .

[13]  Wayne Nelson,et al.  Applied life data analysis , 1983 .

[14]  Fp Gerstle,et al.  Prediction of Long-Term Failure in Kevlar 49 Composites , 1983 .

[15]  Henry Eyring,et al.  Mechanical Properties of Polymeric Materials , 1943 .

[16]  B. D. Coleman.  Application of the theory of absolute reaction rates to the creep failure of polymeric filaments , 1956 .

[17]  V. Shpeizman,et al.  A kinetic treatment of the brittle fracture materials , 1981 .

[18]  M. Northolt.  Tensile deformation of poly(p-phenylene terephthalamide) fibres, an experimental and theoretical analysis , 1980 .

[19]  R. J. Morgan,et al.  Electron paramagnetic resonance studies of Kevlar 49 fibres: Stress-induced free radicals , 1984 .

[20]  S. N. Zhurkov,et al.  Atomic mechanism of fracture of solid polymers , 1974 .

[21]  Bernard D. Coleman,et al.  Statistics and Time Dependence of Mechanical Breakdown in Fibers , 1958 .

[22]  A. J. Pennings,et al.  The fracture process of ultra-high strength polyethylene fibres , 1984 .

[23]  C. N. Robinson,et al.  A comparison of reaction rate models for the fracture of solids , 1970 .

[24]  D. J. Johnson,et al.  Supramolecular structure of a high‐modulus polyaromatic fiber (Kevlar 49) , 1977 .

[25]  S. L. Phoenix,et al.  A statistical model for the time dependent failure of unidirectional composite materials under local elastic load-sharing among fibers , 1983 .

[26]  Lee J. Bain,et al.  Two Sample Tests in the Weibull Distribution , 1969 .

[27]  B. D. Coleman,et al.  The Interpretation of Creep Failure in Textile Fibers as a Rate Process , 1957 .

[28]  D. J. Johnson,et al.  Microvoids in aramid-type fibrous polymers , 1979 .