Contact fatigue

The contact fatigue creates independent part of the fatigue tests. As consequence of triaxial state of stress and flexible plastic state in contact area occurrence comes to very considerable scattering of experimental data. From this reason it is necessary to test statistic meaningful number of samples. 

At contact fatigue tests of different steel and cast iron types was used the acoustic emission technique. Processed records from the AE analyser show importance of acoustic response of tested surface continuous sensing. In graphs are obvious characteristic types of summation curves, or may be from significant changes of AE signal course identified even phases of the wear process. 

YOSHIOKA,T.- MINORU,T. Clarification of Rolling Contact Fatigue Initiation using Acoustic Emission Technique. Lubrication Engineering, Vol.51, No.l, 1995, p.41-44. 

Wear, stress Spalling, rolling contact fatigue... 

Keywords Contact fatigue Toughness Fatigue properties Wear... 

The establishment of the interrelationships between polymer fracture properties and contact fatigue behaviour requires some knowledge of the contact stress field. The specificity of fretting loading is that, depending on the applied contact load and imposed relative displacement, two different contact conditions can be achieved within the interface [54,55] (Fig. 5) ... 

Three successive stages can schematically be distinguished during the course of a contact fatigue test ... 

Fig. 8 Post mortem optical observation of a contact cross-section showing crack depth and orientation within an epoxy polymer after contact fatigue...

Fig. 10 Measured crack lengths, L, in an epoxy polymer as a function of the number of cycles and the imposed lateral displacement. The crack length was measured in the contact plane from in situ observations. Amplitude of the relative displacement Black circles 15 xm, white circles 20 pm, white squares 25 pm, black squares 30 pm, white diamonds 60 pm. Dotted lines indicate the occurrence of britde failure events during the course of the contact fatigue experiments...

Fig. 21 In situ visualization pictures showing damage a in a fretting contact between an unmodified DGEBA/DDM epoxy network and a glass sphere, and b in a similar contact with a DGEBA/DDM network modified with the acetamide derivative shown in Table 1. The magnitude of the maximum tensile stress at the edge of the contact was found to be similar in both cases. Contact fatigue cracks were only observed in the neat DGEBA/DDM system...

As for the epoxy polymers, a quantitative comparison of the contact fatigue behaviour was attempted on the basis of an estimate of the maximum tensile stress at the edge of the contact. The coefficient of friction of the copolymers increased as the tests proceeded, with a variation which was dependent upon the level of the normal loading. As a first approach, the value of //. at crack initiation was taken into account in the calculation of a . The results are reported in a S-N fatigue diagram giving the maximum applied tensile stress as a function of the number of cycles to crack initiation (Fig. 23). These data show a marked increase in the contact fatigue resistance of the GIM copolymers compared with the MIM material. 

Fig. 23 Contact fatigue behaviour of methylmethacrylate random copolymers under fretting conditions. White circle Glutarimide co-monomer (76%), black circle cyclohexyl malemimide co-monomer (25%). The maximum value of the tensile stress has been calculated at the edge of the contact, where cracks initiate, and for values of the coefficient of friction measured at crack initiation...

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