Belt failure cord separation

A dynamic test developed at Hanover University has established the relationship between cord diameter, cord separation and splice strength. In this test, samples received cyclic tensile loads to failure. An optimum cord separation of 1/2 diameter was established, but 1/3 diameter is used for practical purposes on heavy belts, and 1.5 mm rubber between cords,... 

Test results from experimental studies on belt life suggest the following as the major belt failure modes tooth root cracking, wear, cord failure and fabric separation [14,15,16, 17, 18], and this classification has support from field data [19, 20]. Figure 12.2 shows examples of tooth root cracking, cord delamination and fabric separation failures. 

Figure 12.2 Synchronous belt failure modes, a) tooth root cracking, b) cord delamination, c) fabric separation...

Fabric separation failure occurs when the belt teeth and fabric land become detached from the belt cords [17] and is essentially seen as purely an adhesion failure, although there may be links between this failure mode and the tooth root cracking failures observed by lizuka [18], originating from cracks developed in the cord itself through internal delamination. Wear causes belt failure through changing the tooth profile to such an extent that the belt teeth can no longer support the required load [25]. 

In attempting to identify parameters which allow the belt life to be predicted within the adhesion related failure modes identified above, the most common approach has been to use measures of belt distortion. Dalgarno [17] examined belt life data from belt failures within the tooth root cracking, fabric delamination and cord separation failure modes. 

Gerbert and Fritzson also developed a procedure for predicting belt life within the cord separation failure mode, based on the shear stress in the cushion region. The overall shear stress arises from four individual components of shear stress ... 

Of these shear stress components i), ii) and hi) all act along the length of the belt, with iv) acting across the belt width. The combined effect of these four shear stresses is shown to have a good correlation with belt life where cord separation is the failure mode, and is used as part of a belt life prediction procedure (based on finite element analysis) which encompasses all the failure modes identified by Gerbert and Fritzson. 

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