Flex fatigue

The commonest way of studying flex fatigue in fibres is to pull a fibre backwards and forwards over a pin. Typically the pin diameter is about ten times the fibre diameter, giving a nominal bending strain of 10%, and the tension is about 1/10 of the fibre break load, but the mode of failure depends on the exact conditions. In Kevlar and wool fibres 

Tensile fatigue breaks, (a-d) Nylon, (e-g) Polyester. For further explanation, see Fig. I. 

---

Compression Set. The compression set is an important property ki cushioning appHcations. It has been studied for polyurethane foams (185,186), and has been discussed ki reviews (32,60,156). Compression set has been described as flex fatigue and creep as weU. 

In tires, carbon black is important because of the high flex fatigue and tear strength requirements of this product. Poor dispersion can result in premature cracking in both treads and sidewalls. In off-the-road tires poor dispersion results in excessive chip/chunk causing a significant loss in treadwear in addition to tread lug cracking which can lead to loss of an entire lug (radial tread bar). 

In a typical process a preform billet is produced by compacting a mixture of 83 parts PTFE dispersion polymer and 17 parts of petroleum ether (100-120°C fraction). This is then extmded using a vertical ram extruder. The extrudate is subsequently heated in an oven at about 105°C to remove the lubricant, this being followed by sintering at about 380°C. By this process it is possible to produce thin-walled tube with excellent flexing fatigue resistance and to coat wire with very thin coatings or polymer. 

The fluorine content of II gives it excellent resistance to fuels, oils, most hydraulic fluids and chemicals. Since there are no C-C and C-H bonds along the polymer backbone, II displays excellent resistance to degradation by atmospheric oxygen and ozone. Tn addition, the Inherently flexible nature of the P-N backbone allows this elastomer to be used at temperatures down to -65°C, and gives the polymer excellent flex fatigue resistance over a broad temperature range (-65 to 175°C). 

TPU applications are in soling materials, ski boots, industrial belting, and in wire cable needing good tear strength, abrasion resistance and flex fatigue endurance. 

MPRs are handicapped by a lower elasticity than conventional rubbers, the more so the higher the hardness certain risks of creep, relaxation and permanent set, the more so the higher the temperature sometimes limited flex fatigue resistance ecological problems involved with halogens tool corrosion risks lack of sources cost. 

COPEs are appreciated for their high mechanical performances tenacity excellent abrasion and tear resistances good flex fatigue resistance high moduli resistance to ozone, oils... 

The sidewall compound is compounded to protect the ply and must possess resistance to weathering, ozone, abrasion, and tearing while providing excellent flex fatigue resistance. The innerliner compound must provide good air-permeation resistance and resist moist/hot air aging. The inside of a hot... 

Like HIIR, EPR has a fully saturated backbone and has only unsaturation points available for vulcanization cross-linking in very small percentages of the pendent diene modifier (EPDM). It is an excellent aging compound with high flex fatigue life even when heavily loaded with fillers and is utilized in PCT white sidewalls. 

Copolyesterether elastomers have excellent resistance to flex fatigue. For example, in the Ross flex test (ASTM D1052), all of the samples listed in Table 13 resisted cut-growth over 300,000 cycles. 

The British Standard is identical and numbered as BS ISO 132. ASTM has several flexing fatigue methods and it can be seen from the lack of uniformity in the titles that they were not developed as a group. 

ASTM D623,1999. Heat generation and flexing fatigue in compression. 

Flex Fatigue Life 4-100 fold — 100 fold -1000 fold... 

Because of the variation in folding endurance results, it is necessary that many tests be run on a paper to produce a reliable mean. At the Barrow Laboratory, fifty tests were standard. This takes time, but a rate plot based on a few tests per point is of doubtful value. There is a need for an improved folding endurance tester or an entirely new instrument for reliably and conveniently measuring flex fatigue. 

Single-fiber flex fatiguing is studied also. Researchers have sug-... 

Figure 8. Fracture by flex fatigue of a wool fiber of similar type to that of Fiaure 2. Samvle was fractured at 65% rh and 21 °C (442X).

---