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A. Riemer et alii, Frattura ed Integrità Strutturale, 34 (2015) 437-446; DOI: 10.3221/IGF-ESIS.34.49 444 “hollow section” it becomes clear that due to lower maximum stresses and lower weight, the variant “hollow section” exhibits more potential for optimisation. Consequently, this structure design will be optimised in detail in following studies. Figure 9 : Numerical stress analysis results for different load cases b) resulting from various bicycle crank angles a) and maximum displacement results c) . Data for the mass are presented in d) . Detailed optimisation of the bicycle crank The detailed optimisation of the selected variant was performed considering static and fatigue strengths. The safety factors here were reduced to a value of 1.5. In addition to titanium alloy Ti-6-4, two further materials, the stainless steel 316L and the aluminium alloy EN AW-7075-T651, were taken into account. During the optimisation process, buckling problems in the region of the walls occurred. For this purpose, additional walls within the hollow structure were designed, cf. Fig. 10b- d. In this way, the stiffness of this structure design was increased. The value of the thickness of interior walls was kept constant at 1 mm. The results of the optimisation are listed in Tab. 1. The highlighted variants represent for each material the bicycle crank with lowest weight and conditions fulfilled. Variant Material Static strength Fatigue strength Displacement v [mm] Weight m [g] 1 mm hollow Ti -5.6 153 1 mm hollow Al -9.2 97 1 mm hollow St -3.5 278 1 mm walls Ti -4.9 187 0.8 mm walls -5.6 177 0.7 mm walls -6.1 171 2 mm walls St -1.9 453 1.7 mm walls -2.1 420 1.5 mm walls -2.3 398 1 mm walls -3 340 2 mm walls Al -5 158 1.5 mm walls -6 139 1 mm walls -8 119 Condition fulfilled Condition not fulfilled Table 1 : Results of part optimisation based on numerical studies.