Impact fatigue resistance and impact abrasion resistance of pearlitic low chromium cast iron

Impact fatigue resistance and impact abrasion resistance of pearlitic low chromium cast iron

Fatigue lation was performed as a function of depth below the surface on samples from two orthogonal orientations. The slip band type and density was ...

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Fatigue lation was performed as a function of depth below the surface on samples from two orthogonal orientations. The slip band type and density was determined as a function of the resolved shear stress acting on the slip planes and their proximity to the surface. In the primary-o, fatigue damage accumulation occurred primarily by slip on basal planes. Evidence of cc+0 and prism slip was also found, but only where the resolved shear stress on the basal planes was low. Significantly, basal slip was identified on planes on which the resolved shear stress was low. In the transformed- /.I phase strain accumulation was wbstantially greater and was accommodated approximately equally on both basal and prism planes. In all cases, strain was a maximum in the surface grains and decreased with depth at a greater rate than the applied stress. Direct TEM evidence of crack nuclei was found. Cracks formed subsurface at stress concentrations on basal planes and grew along the basal plane towards the surface. The crack initiation mechanism is discussed in relation to strain discontinuities, resolved shear and tensile stresses, chemical composition and slip band length. Photomicrographs, 50 ref. Aging effects on the cyclic deformation mechanisms steel. Llnnrs. L., Mrrteo. A.. Iturgqtw. L. und Angludu. M. A&r Motrricrlicl ( 1996) 44. 396773978

of a duplex

stainless

Aging effects on the cyclic deformation mechanisms of an AISI-329 duplex stainless steel have been studied on the basis of the cyclic hardening-softening response, cyclic stresa+ntrain curve and substructure evolution within the mdividual phases,. The cyclic behaviour of an unaged and two aged materials shows. in terms of plastic strain amplitude (Q), three well-defined stages. In the first regime, at low E,,,, no differences are observed among the response of the three materials as a consequence of the dominance of ‘austenitic-like‘ deformation mechanisms for all the materials. In the second regime, at interp,, the cyclic behaviour of unaged material is associated with a mixed mediate ?? ‘austenitic/ferritic-like’ character, mainly due to plastic activity of both phases On the other hand, the cyclic response of aged material within this intermediate E,,, range is rather correlated to ‘austenitic-like’ cyclic deformation mechanisms because of the intrinsic brittleness of the ferritic matrix. A third regime, at relatively large Er+ suggests a synergetic phenomenon of dislocation activity, deformation twinning and demodulation of spinodal microstructure in ferrite that enables this phase to sustain plastic deformation. Thus, in this E,,, interval. the observed mechanical and substructural behaviour within ferrite may be considered as relatively similar to that observed in unaged material at much lower stress levels; and therefore is amenable to be associated with ‘ferriticlike’ cyclic deformation mechanisms. Finally, based on the results presented. the prevalence of ‘austenitic-like’ or ‘ferritic-like’ cyclic deformation mechanisms, for a given plastic strain range, is discussed in terms of the different role played by the ferritic matrix in each material investigated, depending upon it\ embrittlement degree. Graphs, numerical data, photomicrographs, 32 ref. Tension~om ression asymmetry of the (001) single crystal nickel superalloy S E 16 under cyclic loading at elevated temperatures. Jioo, F., Rettge. D.. Osterk. W. nnd Ziehs, J. Actci Mtrrrricdia ( 1996) 44. 3933-3942

base

Fully reversed low cycle fatigue tests were conducted on oriented \ingle crystals of the nickel base superalloy SC16 at a constant total strain range of 2.0%. The strain rates were varied from 10m2 to 10.‘~ ’ at 75OOC and the temperatures were changed from 650 to 950°C under the strain rate 10~’ 5 ‘ . During cycling under the high strain rates IO-’ and IO-'s ’at 7SO”C or under the strain rate IO ’s ’at 650°C the SC16 single crystals show that the tensile stress (‘0 is higher than the compressive stress (C). During cycling under the low strain rates IO-’ and IOei s ’at 750°C or under the strain rate lO_‘a ’ at 8WC. the cyclic tensioncompression asymmetry of C>7‘ was observed. At 950°C under the strain rate IO ‘so’ no tension-compression asymmetry (1‘= C) was present during fatigue testing. The deformation mechanism corresponding to T>C determined by transmission electron microscopy (TEM) is that the y’ precipitates are sheared by pairs of a/2<] IO> matrix dislocations coupled by antiphase boundaries (APB) within y phase. The reversed asymmetry behaviour (C>7J was found to be associated with the (I I I)< I l2> viscous slip producing superlattice intrinsic/extrinsic stacking faults (SISF/SESF) in y’ precipitates. At 950°C (1‘= C) dislocation climbing over the y’ precipitates becomes the dominant deformation mechanism. Models which can explain the tension-compression asymmetry behaviour were discussed. Graphs, photomicrographa. 32 ref. TS 540-780 N/mm’ grade hot-rolled steel sheets with good formability hiah fatieue strenoth. ‘RHA 540 DH-RHA 780 DH’. M&irct, fi., Kuros&~ N. and [email protected] N. Kowtsnki Steel Technical Report ( 1996) 34, 32-33

and

This paper reports on the features of the TS 54&780 N/mm’ grade hot rolled high-strength steel sheet developed to simultaneously improve formability and fatigue strength, based on a new microstructural control method. Mechanical properties of newly developed steels are presented in the tabular form. Since this hot-rolled high-strength steel sheet has good weldability equivalent to that of HSLA steel, it is expected to be used for a wider range of applications not only in the automotive industry, but also in the construction, civil engineering and machine tool industries. Graphs, numerical data, 1 ref. Impact fatigue resistance and impact abrasion chromium cast iron. He. L. and Zhwg. C. Iron und Steel fChincr) (1996) 31, 48-52

resistance

of pearlitic

low

The effect of carbon and chromium content on the impact fatigue resistance and impact abrasion resistance of pearlitic low chromium cast iron has been

Asbstracts investigated in this paper. The results indicate that better impact fatigue resistance and impact abrasion resistance using sdica as abrasive are obtained when carbon content is 2.37-2.69%. As carbon content changes, the impact fatigue resistance and impact abrasion resistance of pearlitic low chromium cast iron is consistent with its relative toughness which equals bending strength times flexibility. If the chromium content is increased, the comprehensive properties of the cast iron will be improved. The fatigue and fracture behaviour of a y-titanium aluminide intermetallic: influence of ductile phase reinforcement. Sohovejo. W.O.. Ye. F. ond Srivotsctn. T.S. EnRikrring Frttcturr Mechanict ( 1997) 56, 379-39.5 This paper presents the results of recent studies on the ambient temperature fracture toughness and cyclic crack growth characteristics of a ductile-phase toughened y-titanium aluminide intermetallic alloy reinforced with TiNb particles. Under monotonic loading, substantial toughening is achieved in the composite microstructure and is ascribed to bridging of the crack by uncracked TiNb particle reinforcements in the wake of the crack tip. Crack-particle interactions such as crack bridging, bifurcation, deflection and crach renucleation contribute to an enhancement in toughness. Under cyclic loading. ductile phase toughening was found to be less effective resulting in an inferior fatigue crack growth resistance of the composite when compared to the monolithic counterpart. The lower cyclic fatigue resistance is attributed to an increased susceptibility of the ductile phase to fatigue failure. coupled with the mutually interactive influence\ of an absence of bridging contributions to crack-tip shielding, higher crack-tip opening displacements and the intrinsic effects of inelastic strains that are developed in the ductile phawreinforced composite matrix. Photomicrographs, 5 I ref. An investigation of the cyclic fatigue and fracture behaviour of a niobium aluminide intermetallic. Srivotsnn. T.S.. Dipaxpude. .I.. Sohowjo. W.O. ctnd Korritxr. I).(;. Engineering Fracture Mrchonic~ (1997) 56, 293-309 Thi\ paper presents the results of a study designed to improve our understanding of the cyclic fatigue and fracture characteristics of a niobium aluminide intermetallic. Specimens of the intermetallic were deformed to failure in uniaxial tension. fully-reversed total strain amplitude control and cyclic stress amplitude control. The alloy exhibited limited plasticity and life under strain amplitude-controlled fatigue. Cyclic stress controlled high-cycle fatigue characteristics were established at ambient temperature. The cyclic stress response and fatigue fracture characteristics of the intermetallic are presented and discussed in the light of concurrent and mutually interactive influences 01 intrinsic microstructural effects, cyclic stram and stress amplitude. and ductility of the material. The matrix deformation characteristics of the intermetallic during incremental tensile and cyclic loading are presented and discussed in the light of magnitude of load, slip characteristics and mtrinsic microstructural effects. Graph\, photomicrographs, 24 ref. Influence of mean stress on Ti6A14V fatigue crack growth at very high frequency. Bnthics, C.. El Alnmr. K. and Wu. 7: Y. En,r+wrir~g Frrruuw Mechanics ( 1997) 56, 255-264 The present study deals with the fracture mechanics hehaviour of a titanium alloy, Ti6Al4V (TA6V french mark) in ultrasonic fatigue. Besides the development of corresponding experimental techniques, this paper prewns firstly the finite element method calculation of stress intensity factor KDI in ultrasonic fatigue with a positive mean stress: then fatigue crack growth (FCG) rate\ ol Ti6A14V at high frequency at room temperature and with stress ratio R between -I and O-0.9. The thresholds are determined up to - IO.” m/cycle. The fracture mechanisms have been observed and analyzed metallographically and microfractographically under a scanning electron microscope to compare with conventional fatigue. In addition, wme cumulation experiments of ultrasonic fatigue with ‘ilow fatigue have been carried out. Graph\, photomicmgraphs, 7 ref. Mean strain effect on crack initiation lives for notched specimens under biaxial nonproportional loading paths. Yip, M.-C. and Jen, Y.-M. Journol of Engineering Moterirrls rrr~d T~~r~hrrolo~r ,. I Trtrnstlc~tions of the ASMEl (1997) li9. IK4-l I2 ” This paper discusses the mean strain effect on the crack initiation lives for notched specimens under biaxial nonproportional loading paths. Elastic-plastic finite element method was used to evaluate the local stresses and strain\. Several prediction models related to the mean stress/strain effect were employed to correlate the experimental results with reference fatigue data for smooth specimens. It i< found that Fatemi-Socie model gives good prediction for the present research with the assistance of finite element method. The stre\s behaviour in this deflection-controlled test is discussed in this study, and the failure surfaces are also examined after te\ts. Graphs. 34 ref. Probabilistic mesomechanical fatigue crack nucleation model. Trvon. R.G. nrld Cruse. T.A. J&ma1 of Engineering Motrrinls rend Techno/og\ (7nrn.wction.s qf rhe ASME) (1997) 119. 65-70 A probabilistic mesomechanical crack nucleation model is proposed to lmk the microstructural material heterogeneities to the statistical scatter in the macrostructural response. The macrostructure is modelled as an ensemble of microelements. Cracks nucleate within the microelements and grow from the