Mechanical behaviour of conventional and negative Poisson’s ratio thermoplastic polyurethane foams under compressive cyclic loading

High-performance commodity polymers are in demand due to low cost, durability, easy productivity, and recycling ability. This article comprises a survey on the performance properties of polytetrafluoroethylene (PTFE) fluoropolymer. It is a well-known choice for coatings, insulation, thermal sealing, lubrication, bearings, and clinical applications. PTFE was engineered in many forms as a function of loading nano and micro fillers for different purposes and the improved properties and performance were addressed by the researchers. Hence, we disclosed the various casting routes of PTFE which is feasible for reliable processing to serve in domestic and industrial applications.

Performance properties and applications of polytetrafluoroethylene (PTFE)—a review

The role of crystalline phase on fracture and microstructure evolution of polytetrafluoroethylene (PTFE)

The effect of crystallinity on the fracture of polytetrafluoroethylene (PTFE)

The swelling-driven fatigue behavior of polymer fuel cell membranes during relative humidity (RH) cycling is investigated. In particular, swelling-induced membrane stresses are obtained from a numerical model simulating fuel cell RH cycle tests, and compared to the lifetimes obtained experimentally from tests conducted in the absence of electrochemical effects. A strong correlation between the lifetimes of the membranes in the actual tests and model results is obtained. In general, higher RH (or swelling) amplitude results in larger stress amplitudes and shorter lifetime, that is, fewer cycles to failure. Tensile stresses are needed for forming local cavities in the membrane, which may eventually lead to craze formation. Cavitation is less likely to occur in compressed membrane at high humidities. The stress–lifetime plots for polymer fuel cell membranes exhibit similar features to those observed for other polymers. The crazing criterion for polymers suggests that craze initiation during RH cycling is more likely to occur in the low compression regions, such as under the channels, which is in agreement with experimental observations. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1506–1517, 2011

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Aspects of Fatigue Failure Mechanisms in Polymer Fuel Cell Membranes

Polytetrafluoroethylenes (PTFEs) and their composites are a special class of fluorocarbons with very high chemical resistance and wide service temperature. This makes them good candidate materials for load-bearing components exposed to harsh environments, including some space applications. In the present work, fatigue crack propagation (FCP) behavior of four materials from the fluorocarbon family, including PTFE without filler (virgin PTFE), PTFE with 15% glass fiber, PTFE with 15% graphite particles, and PTFE with 25% glass fiber, were studied. Tension/tension FCP experiments were carried out using single-edge notch (SEN) specimens under load control. The maximum stress was kept constant at 8 MPa for each material at a frequency of 3 Hz. The minimum to maximum stress ratio was 0.27. FCP data such as the number of cycles, crack length, and hysteresis loops were recorded in order to establish the crack speed, the energy release rate, J*, and the change in work Wɛi. Parameters that characterize the resistance of PTFEs to FCP have been successfully determined by the modified crack layer (MCL) model. These parameters are γ′, the specific energy of damage, which reflects the FCP resistance of the PTFE materials, and the dissipative characteristic of the materials, β′. It has been found that the MCL model describes the behavior of the PTFEs over the entire range of the energy release rate and discriminates the subtle effects introduced by changing the filler type and dosage as well as the processing conditions. The values of the specific energy of damage γ′ have been found to decrease by increasing the dosage of the fiberglass fillers. Graphite particulate filler also reduced the value of γ′ more than fiberglass filler for the same dosage. Microscopic analysis of the fracture surface in the stable crack propagation region of each material revealed that there exists a strong correlation between the value of γ′ and the amount of damage energy manifested by different mechanisms and species during the fatigue process.

Evaluation of the fatigue fracture resistance of unfilled and filled polytetrafluoroethylene materials

Correlation between the dynamic mechanical properties and the fatigue behavior of filled and unfilled PTFE materials

The fracture and fatigue behavior of 15% chopped glass fiber reinforced PTFE was studied. Two fracture regions were observed with the static tensile failure of this material. Torn ligament bundles. pulled out fibers and microfibrillation are the fracture surface features associated with the first region. These features were responsible for the initial slow crack observed during tensile loading. The second region was characterized by a smoother surface with little damage associated features resulting in an unstable crack propagation. The Modified Crack Lajer Model was used to analyze the fatigue crack propagation behavior of the material. The fatigue fracture surface of the 15% glass fiber reinforced PTFE showed three distinct regions. These regions were comparable in location with the three stages of fatigue crack propagation (FCP) kinetics of this material. A large number of torn fracture ligaments and long fibrils were observed in the first region, which is associated with the threshold state of FCP. Extensive random fibrillation was found in the second fracture region which was associated with the second stage of FCP kinctics (stage of reduced acceleration). Undrawn matrix, very little fibrillation and a smooth surface were the fracture surface features of the third region. This region was associated with the third stage, unstable crack propagation. of FCP kinetics.

Fracture and Fatigue Analysis of 15% Chopped Glass Fiber Reinforced PTFE

Chronic inflammation is frequently associated with myeloproliferative neoplasms (MPN), but the role of inflammation in the pathogenesis of MPN remains unclear. Expression of the proinflammatory cytokine interleukin-1 (IL-1) is elevated in patients with MPN as well as in Jak2V617F knock-in mice. Here, we show that genetic deletion of IL-1 receptor 1 (IL-1R1) normalizes peripheral blood counts, reduces splenomegaly and ameliorates bone marrow fibrosis in homozygous Jak2V617F mouse model of myelofibrosis. Deletion of IL-1R1 also significantly reduces Jak2V617F mutant hematopoietic stem/progenitor cells. Exogenous administration of IL-1β enhances myeloid cell expansion and accelerates the development of bone marrow fibrosis in heterozygous Jak2V617F mice. Furthermore, treatment with anti-IL-1R1 antibodies significantly reduces leukocytosis and splenomegaly, and ameliorates bone marrow fibrosis in homozygous Jak2V617F mice. Collectively, these results suggest that IL-1 signaling plays a pathogenic role in MPN disease progression, and targeting of IL-1R1 could be a useful strategy for the treatment of myelofibrosis. 

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Interleukin-1 contributes to clonal expansion and progression of bone marrow fibrosis in JAK2V617F-induced myeloproliferative neoplasm

The effect of filler type on the fatigue fracture mechanisms of polytetrafluoroethylene (PTFE) composites was studied. The two composites were a silica particle filled PTFE (Garlock 3502‘) and a glass fiber filled PTFE (Garlock 8573‘). Tension-tension fatigue crack propagation tests were conducted on both materials at room temperature at a frequency of 3 Hz. The maximum stress was 6 MPa and the ratio of minimum load to maximum load was 0.1. It was found that the fatigue lifetime of the particle filled PTFE is approximately four times higher than that of the fiber filled PTFE. The fatigue data also revealed that the crack speed of the particle filled composite is always lower than that of the short fiber filled composite. Microscopic analysis on representative fracture surface of each material was performed to identify different fracture surface features. The three fracture regions, crack initiation, stable crack growth and unstable crack growth were examined. In the first region, both composites displayed...

P. Faughnan

Papers

Evaluation of the fatigue fracture resistance of unfilled and filled polytetrafluoroethylene materials

Correlation between the dynamic mechanical properties and the fatigue behavior of filled and unfilled PTFE materials

Fracture and Fatigue Analysis of 15% Chopped Glass Fiber Reinforced PTFE

Interleukin-1 contributes to clonal expansion and progression of bone marrow fibrosis in JAK2V617F-induced myeloproliferative neoplasm

Fatigue Fracture Mechanisms of Particle and Fiber Filled PTFE Composites