Fracture mechanics of high performance nylon fibers

Journal of Applied Polymer Science, 1998

The effect of relative humidity on the fracture energy release rate, G Ic , for single nylon 6,6 fibers has been determined previously. In this article, it is shown that G Ic is independent of relative humidity for moisture contents of ú 2.3% once the plastic zone correction is made. G Ic is compared with various proposed mechanisms to account for fracture energy. It is shown that the energy required to disrupt or ''melt'' the crystals in the plastic zone accounts for the majority of the energy required to break the specimen, and should be considered explicitly in future analyses of fracture in semicrystalline polymers.

Polymer Engineering and Science, 1978

Nylon 6 fibers which had been relaxed to different extents by annealing were examined at fixed strains by small angle and wide angle X-ray techniques. It was found that the strain of the long period of the semicrystalline microfibrils is identical to the macroscopic fiber strain. Approximately % of the tensile deformation results from molecular shear of imperfectly oriented crystalline chains. Virtually no evidence for intercrystalline slip is found; the orientation of the intercrystalline amorphous regions results in a low compliance for the shear of crystals past one another. The majority of the microfibril deformation occurs by stretching these intercrystalline amorphous regions, accompanied by the flow of extrafibrillar amorphous material to maintain constant volume. In highly annealed fibers this "filling" mechanism is less efficient, as the amount of extrafibrillar material has been reduced during shrinkage. This effect leads to a decrease in Poisson's ratio after increasingly severe annealing. A related result of annealing is the dehomogenization of the microstructure, leading to the presence of more stress-induced "microcracks" during the stretching of annealed fibers.

2009

The research purposes to implement fracture based approach in failure analysis of nylon 600 fiber and also partly embedded nylon 600 fiber in cementitious matrix. The methods are experiment and analytical by modeling. The experiment activities consist of tension test of nylon 600 fiber and pullout test of partly embedded nylon 600 fiber in cementitious matrix with length 150 mm and 180 mm. The research meets conclusions: (1) Whenever fracture takes place, it is always an unstable crack; (2) Stable cracks are established by the presence of crack arrester; (3) After the establishment of stable cracks, increasing strain beyond strain  1 will not increase stress  1 , hence do not induce additional fracture; (4) Increasing of strain after the establishment of stable cracks in point g will increase stress, the second slip will not take place; (5) Broken nylon fibers have a longer embedded length because of the possibility of crack arrester presence is bigger than the shorter ones; and (6) Since the middle right side of matrix is at the intersection point with fiber acts as crack arrester in the beginning of pull-out process, then the load-displacement (P- and stress-strain () curves of pull-out test will be the same as the load-displacement (P-and stress-strain () curves of fiber tension test.

Polymer, 2001

The impact fracture parameters of blends of nylon 6 and maleated ethylene±propylene rubber (EPR-g-MA) reinforced with glass ®bers as a function of glass ®ber and EPR-g-MA content were examined. Both the linear elastic fracture mechanics (LEFM) model and a modi®ed essential work of fracture (EWF) model were used to analyze the data. It was found that the addition of EPR-g-MA to unreinforced nylon 6 increased the EWF parameters u o and u d de®ned by U=A u o 1 u d`; where U/A is the total fracture energy per unit area and l is the ligament length. Beyond a critical rubber content, which coincided with the ductile-to-brittle transition, there was a large increase in u d. When glass ®ber reinforcement was used without rubber toughening, the EWF model was unable to model the observed fracture response. On the other hand, the LEFM model adequately described the fracture behavior, and it was found that the critical strain energy release rate, G IC , increased with increasing glass ®ber content. When both glass ®ber reinforcement and rubber toughening were used, the u o increased with increasing EPR-g-MA or glass ®ber content; whereas, u d increased with increasing ERR-g-MA content or decreasing glass ®ber content.

Journal of Materials Science, 1984

Nylon 6 fibres were irradiated with up to 60 Mrad of cobalt-60 gamma radiation in air or up to 76 #C of 4.5 MeV cyclotron-accelerated protons in vacuum. The products of the irradiations were then characterized by the resulting changes in ultimate mechanical properties and in fracture morphology when tested at 21~ under selected conditions of fibre moisture content. In general, the results show a progressive deterioration of tensile properties, an increase in torsional brittleness, and a decreasing flex life, with increasing dose, and display some dependence onfibre moisture content. The effects are most pronounced in the first interval of dose; i.e. 10 Mrads gamma irradiation and 12/~C of high energy protons. The rate of deterioration of these mechanical properties generally slows with subsequent dose increases. An annulus/core fracture morphology was found in the gamma-irradiated material which was not in evidence for material irradiated with protons in vacuum. The morphology of the proton-irradiated tensile breaks are characteristic of a brittle material; flex fatigue fracture surfaces were often characterized by step-like formations reminiscent of kink bands. Discussion of the data in terms of radiochemical processes, structure-property relations, and implications for accelerated ageing programs are included.

Journal of Materials Science, 2004

Hybrid composite systems consisting of liquid crystalline polymer (LCP), short glass fibers and toughened nylon in varied ratios were studied. Dynamic mechanical results indicated that, elastomeric phase in toughened nylon 6,6 promoted a better compatibilization between nylon 6,6 and LCP in a hybrid system containing short glass fibers in comparison with one without glass fibers. Improved compatibility facilitated fibrillation of LCP phase in the skin region of the hybrid composite, thereby providing superior tensile strength. Without the presence of LCP, glass fiber reinforced toughened nylon 6,6 exhibited the least tensile strength. J-integral analysis and essential work of fracture (EWF) method were used to compare the fracture behavior of composites. Results showed that specific essential work of fracture were consistent with the critical J-integral. Matrices reinforced by LCP alone showed (Shing-Chung Wong) 2 best crack initiation and propagation toughnesses, followed by glass fiber reinforced and hybrid composites. The better compatibility between nylon 6,6 and LCP appeared to inhibit the interfacial debonding process, resulting in brittle fracture.

Wear, 1976

2002

The toughening behavior of short glass fiber reinforced toughened polymers was studied using fracture mechanics and microscopic techniques. The essential work of fracture (EWF) analysis shows that the inclusion of short glass fibers not only provided a stiffening effect but also a toughening influence. It was observed that rubber-related toughening and fiber-related toughening were competitive in nature for the reinforced, toughened nylon 6,6. When the matrix stress was substantially reduced by the presence of short fibers via the load-shedding mechanism, rubber toughening was severely curtailed. At higher fiber volume fractions, fiber pull-out work contributed significantly to the enhancement of the specific essential fracture work. Fiber-end plasticity was evident under microscopic examination.

Journal of Materials Science, 1993

The effect of filament diameter on the failure stress of polyethylene fibres has been studied using Weibull analysis. Both gel-spun and melt-spun fibres have been examined, so that differences might be observed for changes in draw ratio or modulus as well as molecular weight. It is concluded that the strength of high-modulus melt-spun fibres relates to the concentration of flaws and is significantly dependent on filament diameter. Conflicting results for gel-spun fibres are discussed in the light of the present investigation, and it is concluded that the mechanism of failure in these fibres is different from that of the melt-spun fibres.

Polymer, 2000

The impact fracture parameters of blends of nylon 6 and maleated ethylene±propylene rubber (EPR-g-MA) reinforced with glass ®bers as a function of glass ®ber and EPR-g-MA content were examined. Both the linear elastic fracture mechanics (LEFM) model and a modi®ed essential work of fracture (EWF) model were used to analyze the data. It was found that the addition of EPR-g-MA to unreinforced nylon 6 increased the EWF parameters u o and u d de®ned by U=A u o 1 u d`; where U/A is the total fracture energy per unit area and l is the ligament length. Beyond a critical rubber content, which coincided with the ductile-to-brittle transition, there was a large increase in u d. When glass ®ber reinforcement was used without rubber toughening, the EWF model was unable to model the observed fracture response. On the other hand, the LEFM model adequately described the fracture behavior, and it was found that the critical strain energy release rate, G IC , increased with increasing glass ®ber content. When both glass ®ber reinforcement and rubber toughening were used, the u o increased with increasing EPR-g-MA or glass ®ber content; whereas, u d increased with increasing ERR-g-MA content or decreasing glass ®ber content.