Experimental evaluation and statistical characterization of the strength and strain energy density distribution of Kevlar KM2 yarns: exploring length-scale and weaving effects

Abstract

This article experimentally investigates the tensile strength distributions of 600 den Kevlar KM2 yarns under quasi-static tensile loading. The strength distributions were best characterized using the 3-parameter Weibull and generalized Gamma distributions. In order to assess the effects of weaving on the strength distributions, Kevlar yarns were tested from a spool and then compared to yarns extracted from greige and scoured Kevlar fabrics. The weaving process and treatments caused various levels of strength degradation which shifted the strength distributions toward lower strengths. The warp yarns were degraded to a greater extent than the fill yarns. The scouring process induced further strength degradations in the woven fabric. Length-scale effects were studied by using gage lengths varying between 25.4 and 381.0 mm. The strength distributions were observed to shift toward lower strengths with increasing gage lengths. A new distribution function based on a modification to the 3-parameter Weibull distribution is proposed to account for length-scale effects. In addition to the strength distributions, the experimental load—extension plots are used to compute the strain energy density or work-to-break values normalized by the yarn volume, which are then statistically characterized and analyzed in a similar manner.

Keywords

polymer Kevlar KM2 tensile testing yarn strength statistical analysis cumulative distribution function length scale weaving effects

Get full access to this article

View all access options for this article.

References

Steenbakkers LW and Wagner HDE. Elasticity and mechanical breakdown of Kevlar 149 aramid fibres by a probabilistic approach. J Mater Sci Lett 1988; 7(11): 1209-1212.

Wang Y. and Xia Y. Experimental and theoretical study on the strain rate and temperature dependence of mechanical behavior of Kevlar fiber. Composites Part A 1999; 30: 1251-1257.

Schwartz P. , Netravali A. and Sembach S. Effects of strain rate and gauge length on the failure of ultra-high strength polyethylene fibers. Text Res J 1986 ; 56(8): 502-508.

Goda K. and Fukunaga H. The evaluation of the strength distribution of silicon carbide and alumina fibres by a multi-modal Weibull distribution. J Mater Sci 1986; 21(12): 4475-4480.

Farsi Dooraki B. , Nemes JA and Bolduc M. Study of parameters affecting the strength of yarns. J Phys IV France 2006; 134: 1183-1188.

Amaniampong G. and Burgoyne CJ Statistical variability in the strength and failure strain of aramid and polyester yarns. J Mater Sci 1994; 29(19): 5141-5152.

Wu HF and Netravali AN Weibull analysis of strength-length relationships in single Nicalon SiC fibres . J Mater Sci 1992; 27(12): 3318-3324.

Loidl D. , Paris O. , Rennhofer H. , Muüler M. and Peterlik H. Skin-core structure and bimodal Weibull distribution of the strength of carbon fibers. Carbon 2007; 45(14): 2801-2805.

Leal AA , Deitzel JM and Gillespie Jr JW Assessment of compressive properties of high performance organic fibers . Compos Sci Technol 2007; 67: 2786-2794.

10.

Watson A. and Smith R. An examination of statistical theories for fibrous materials in the light of experimental data. J Mater Sci 1985 ; 20(9): 3260-3270.

11.

Phoenix SL , Schwartz P. and Robinson HHI Statistics for the strength and lifetime in creep-rupture of model carbon/epoxy composites. Compos Sci Technol 1988; 32: 81-120.

12.

Haque A. , Mahmood S. , Walker L. and Jeelani S. Moisture and temperature induced degradation in tensile properties of Kevlar-graphite/epoxy hybrid composites. J Reinf Plast Compos 1991 ; 10(2): 132-145.

13.

Auerbach I. Kinetics for the tensile strength degradation of nylon and kevlar yarns. J Appl Polym Sci 1989; 37(8): 2213-2227.

14.

O’Neil JM Factors contributing to the degradation of PBO fibers under elevated temperature and humidity conditions. Master of Science Thesis, Department of Mechanical Engineering, Texas A&M University, USA, August 2006.

15.

Said MA , Dingwall B. , Gupta A. , Seyam AM , Mock G. and Theyson T. Investigation of ultra violet (UV) resistance for high strength fibers . Adv Space Res 2006; 37(11): 2052-2058.

16.

Gu H. Ultraviolet treatment on high performance filaments. Mater Des 2005; 26(1): 47-51.

17.

Dobb MG , Robson RM and Roberts AH The ultraviolet sensitivity of Kevlar 149 and Technora fibres. J Mater Sci 1993; 28(3): 785-788.

18.

Lee L. , Rudov-Clark S. , Mouritz AP , Bannister MK and Herszberg I. Effect of weaving damage on the tensile properties of three-dimensional woven composites. Compos Struct 2002; 57: 405-413.

19.

Abu-Obaid A. , Andersen SM , Gillespie Jr JW , et al. Effects of weaving on S-2 glass tensile strength distributions . In: 9th International Conference on Textile Composites , Newark, DE, USA, 13-15 October, 2008 .

20.

Abu-Obaid A. , Andersen SM , Gillespie Jr JW , et al. Effects of 3D weaving on tensile strength retention of Z-tows . In: Second World Conference on 3D Fabrics and their Applications, Greenville, South Carolina, USA, 6-7 April, 2009.

21.

Dobb MG , Johnson DJ and Saville BP Compressional behavior of Kevlar fibers. Polymer 1981; 22: 960-965.

22.

Hill R. and Okoroafor EU Weibull statistics of fibre bundle failure using mechanical and acoustic emission testing: the influence of interfibre friction. Composites 1995; 26(10): 699-705.

23.

Wang Y. and Xia Y. The effects of strain rate on the mechanical behavior of Kevlar fiber bundles: an experimental and theoretical study. Composites Part A 1998; 29A: 1411-1415.

24.

Weibull++ Version 7, Reliasoft Corporation , http://weibull.reliasoft.com.

25.

Nilakantan G. , Showell C. , Abu-Obaid A. , et al. An experimental and numerical study of the impact response (V50) of flexible plain weave fabrics: accounting for statistical distributions of yarn strength. In: 1st Joint American-Canadian International Conference on Composites and the 24th Annual ASC Technical Conference, University of Delaware , Newark, DE, USA, 15-17 September, 2009.

26.

Briscoe BJ and Motamedi F. Role of interfacial friction and lubrication in yarn and fabric mechanics . Text Res J 1990; 60(12): 697-708.

27.

Duan Y. , Keefe M. , Bogetti TA , Cheeseman BA and Powers B. A numerical investigation of the influence of friction on the energy absorption by a high-strength fabric subjected to ballistic impact. Int J Impact Eng 2006; 32: 1299-1312.