Damage development in titanium metal.nmUqx ~ subjected to cyclic lo~lng. Johnson, W.S. Composites (1993) 24 (3), 187-196

For several lay-ups of SCS-6/Ti-15-3 (Ti-15V-3Cr-3AI-3Sn) composites, fatigue tests were conducted and analysed for both notched and unnotched specimens at room and elevated temperatures. Thermomechanical fatigue results were also analysed. Test results indicated that the stress in the 0 ° fibres is the controlling factor in fatigue life. The static and fatigue strengths of these materials are shown to be strongly dependent on the level of residual stresses and the fibre-matrix interfacial strength. Fatigue tests of notched specimens showed that cracks can initiate and grow many fibre spacings in the matrix material without breaking the fibres. Fibre-bridging models were appfied to characterize the crack growth behaviour. The matrix cracks are shown to reduce significantly the residual strength of notched composites. The notched strength of these composites was accurately predicted using a micromechauics-based methodology. Photomicrographs, graphs, 22 ref.

ERects of interface degradation on fibre bridging of composite fatigue cracks. Chan, K.S. Acta Metall. Mater. (Mar. 1993) 41 (3), 761-768

A theoretical analysis that examines the effects of cyclic degradation of interface on fibre bridging of fatigue cracks in metal-matrix or intermetallic- matrix composites is presented. Using fibre-bridging models and crack-tip micromechanics results available in the literature, the frictional stresses on individual fibre-matrix interfaces located within the bridging zone in the wake of a fatigue crack in a SCS--6/Ti-6AI-4V composite are calculated. The results are used to demonstrate that a reduction of the interface friction stress by fatigue can lead to a decrease of the fibre-bridging stress, and an increase in the near-tip stress intensity range. The consequence is that the near-tip stress intensity range and, thus, the crack growth of a bridged fatigue crack are sensitive to cyclic interface degradation and the distribution of the frictional stress within the bridged zone. Graphs, 24 ref.

A simple reliability model for the fatigue failure of repairable offshore structures. Connoily, M.P. and Hudak, S.J. Jr Fatigue Fract. Eng. Mater. Struct. (Feb. 1993) 16 (2), 137-150

A simple reliability model for fatigue failure of (structural steel) tubular welded joints used in the construction of offshore oil and gas platforms is proposed. The stress-life data obtained from large-scale fatigue tests conducted on tubular joints are used as the starting point in the analysis and are combined with a fracture mechanics model to estimate the distribution of initial defect sizes. This initial defect distribution is hypothetical but it agrees well with other initial defect distributions quoted in the literature and, when used with the fracture mechanics model, results in failure probabilities identical to those obtained from the stress-life data. This calculated distribution of initial defect sizes is modified as a result of crack growth under cyclic loading, and the probability of failure as a function of fatigue cycles is calculated. The failure probability is modified by inspection and repair, and the results illustrate the trade-off between inspection sensitivity and inspection interval for any desired reliability. Graphs, 17 ref.

Tribological behavior of a tttonlum-nickel alloy. Clayton, P. Wear (13 Apr. 1993) 162-164, (A), 202-210

Titanium-nickel alloys based on the unusual intermetallic compound TiNi exhibit a ductility comparable to metallic alloys. The primary interest in these materials has focused on their shape-memory alloy effects. The mechanical behavionr of a titanium-55 Ni alloy in sliding and rolling/sliding contacts has been investigated. The purpose was to examine the potential of the material as a rim for a locomotive wheel. The possible benefits include an enhancement of the coefficient of friction between wheel and rail under the typical conditions of mild contamination. Wear tests were carried out under non- lubricated conditions to compare the material with conventional pearlitic steel. The Ti-Ni alloy exhibits a high resistance to wear under severe contact conditions. It also gives excellent resistance to water-lubricated rolfing contact fatigue when run against itself. In tests of Ti-Ni alloy on steel, some steel rollers failed at very short lives and others wore and did not experience fatigue. The wear and rolling contact fatigue results are discussed in the context of monotonic and cyclic stress-strain properties. The capacity of TiNi for cyclic strain hardening is considered to be very significant. Steels used include BSl l , D5594, and class D tyre steel. Graphs, 22 ref.

Performance of steel bridge decks with polymer screeds. Hassan, M.E.-S. Diss. Abstr. Int. (Mar. 1993) 53 (9)

An experimental coating material for steel bridge decks, based on a resinous binding material, has been investigated. The resin materials used were mainly copolymers of methyl methacrylate (MMA) and n-butyl methacrylate (NBMA) monomers with different blend ratios. The coating material comprised the resins as binding material and silica sand as aggregate with different mix ratios. This material is designed to be laid with a thickness of 10-12 nun to provide a smooth riding surface with higher fatigue life than the traditional mastic asphalt. The reduction in the dead weight due to application of this material reaches > 75% compared with mastic asphalt, which is normally laid 38-50 mm thick, and the fatigue life is improved by more than ten times that achieved by mastic asphalt. The objectives were to obtain a full assessment of the properties of this experimental material, to produce comparison with mastic asphalt wherever possible, and to recommend the best kind of copolymer for different ambient conditions. Since the designed coating materials, based on different kinds of resinous binders, showed linear behaviour at different temperatures, two linear elastic theories were used for

Fatigue Abstracts

the theoretical analysis. These were the simple bending and stress function theories, which showed very good agreement with experimental results. The stiffness of different resin-based materials was calculated from the experimental results by using the theoretical solution at different loading conditions and then this was used to evaluate the stresses imposed on the bridge deck. The stress reduction in the steel deck plate due to different resin-based materials under different loading conditions was evaluated by the simple beam theory on layered steel beams.

Rolnng-contoct-fatigue were" characteristics of diamond-like hydrocarbon emtini~ on geels. Wei, R.H., Wilbur, P.J., Liston, M.-J. and Lux, G. Wear (13 Apr. 1993) 162-164, (A), 558-568

Adherent diamond-fike hydrocarbon (DLHC) coatings were applied on AISI M-50, 52100, 4118, and 440C steel rods by using an approx 0.2 pan amorphous- silicon-hydrocarbon (a-SiHC) bonding layer between the DLHC and the steel. Both the a-SiHC and DLHC coatings were applied using a single, broad-beam ion source. The rods were subjected to rolling-contact-fatigue (RCF) testing under high, cyclic Hertzian stress (5.5 GPa), low lubricant- film-thickness parameter (k = 0.7) conditions. Order-of-magnitude increases in the fatigue lives of all four rod materials were observed. Systematic RCF tests coupled with microscopic examination after various test intervals show that micropolishing by hard DLHC coating fragments may play an important role in prolonging fatigue lives. Raman spectroscopic measurements suggest that cyclic stressing of the DLHC layer causes it to transform from what was initially amorphous carbon into the more lubricous and stable graphite phase. Photomicrographs, spectra, graphs, 21 ref.

Lubricated ~ and rolling wear of anstempeced ductile iron. Zhou, pC.. S., Zhou, Q.-D. and Meng, S.-K. Wear (13 Apr. 1993) 162-164, (B), 696-702

A series of anstempered ductile iron samples was prepared by varying the austeuitizing temperature and austempering temperature. The lubricated sliding and rolling wear were studied and the wear mechanisms discussed. The results showed that for lubricated sliding wear, the wear resistance decreased with increasing anstenitizing temperature (850-950 °C) and aus- tempering temperature (300-400 °C), and the mechanism was fatigue wear; and for lubricated rolling wear, the wear resistance decreased initially with increasing anstempering temperature (300-400 °C) to a minimum and then increased considerably, and the mechanism was mainly fatigue spalling. It was supposed that a structure composed of lower bainite and low carbon content retained austenite is always beneficial to wear resistance. Hardness was an important property influencing the wear resistance. The hardening due to the phase transformation of retained anstenite contributed to the rolling wear resistance. Photomicrographs, graphs, 6 ref.

Improvement of fatigue life of welding structure by epoxy resin coating, Magara, S. J. Soc. Mater. Sci. Jpn (Jan. 1993) 42 (472), 35-39 (in Japanese)

The breakdown of welded structure is usually caused by fatigue fracture, starting from the toe of the weld. This happens at the welded portion of truck chassis frames and rear axle cases. To improve their fatigue life, the following measures are usually taken: grinding, remelting, shot blasting and shot peening. However, these measures have some problems from the viewpoint of working conditions. It is known that the crack propagation rate is less in vacuum than in air. It is also considered that this fatigue life improvement is larger when the stress concentration factor is larger. Epoxy resin may be used to examine this phenomenon by coating it on the welded portion, but the coated resin also affects the deformation of the crack generation area. So, the effect of epoxy resin coating on fatigue fracture strength was investigated. Welding joints of SAPH440 and $40C steels are discussed. Graphs, numeric data, photomicrographs, 3 ref.

Fractoi analysis of fracture surface of welding joint under low cycle fatigue. Ni, Y.S., Cheng, G.X. and Kuang, Z.B. (in Chinese) Acta Metall. Sin. (China) (Nov. 1992) 2g (11), A498-A505

The Hansdorff dimension of fracture surface roughness of welded joints, both weld metal and heat-affected zone, of pressure vessel steel 16MnR, tested under strain-controlled low-cycle fatigue, was examined with a computer vision system and by a two-dimensionai variation method. The results show that it decreases with increase of the cyclic hysteresis energy. The Hansdorff dimension variation of the heat-affected zone is higher than that of the weld metal. It is believed that the nigher is the fractal dimension, the longer will be the fatigue life. Graphs, photomicrographs, 12 ref.

Study of the effect of defects on the fatigue behaviour and the fracture toughness for low carbon steel (API SL Grade B) gas transmission pipelines. Atwa, G.A.E.A., Mawsouf, N.M. and Younan, M.Y.A. Eng. Fract. Mech. (Apr. 1993) 44 (6), 921-935

The use of low-carbon steel pipes in gas-transmission pipelines and network gas pipes has increased. API 5L grade B (American Petroleum Institute) pipes are welded and inspected according to the BGC/PS code (British Gas Standard). Since root undercut and lack of penetration are common defects, the acceptance and non-acceptance of these defects based on the BGC/PS/ P2 code of butt-welded pipes are evaluated. Pipes are welded with different degrees of root undercut and lack of penetration defects and are X-rayed. The defects are categorized based on both X-ray films and final crack area. Specimens are cut and fatigue-precracked at different periods depending on the initial defect size. An equivalent crack length is calculated based on Paris' law for each defect size in the fatigue crack propagation. The crack

Fatigue, 1994, Vol 16, April 231