De Lorenzo D S, Hull M L
Department of Mechanical Engineering, University of California, Davis 95616, USA.
J Biomech Eng. 1999 Aug;121(4):399-405. doi: 10.1115/1.2798337.
To provide data for fatigue life prediction and testing of structural components in off-road bicycles, the objective of the research described herein was to quantify the loads input to an off-road bicycle as a result of surface-induced loads. A fully instrumented test bicycle was equipped with dynamometers at the pedals, handlebars, and hubs to measure all in-plane structural loads acting through points of contact between the bicycle and both the rider and the ground. A portable data acquisition system carried by the standing rider allowed, for the first time, this loading information to be collected during extended off-road testing. In all, seven experienced riders rode a downhill trial test section with the test bicycle in both front-suspension and full-suspension configurations. The load histories were used quantitatively to describe the load components through the computation of means, standard deviations, amplitude probability density functions, and power spectral density functions. For the standing position, the coefficients of variation for the load components normal to the ground were greater than 1.2 for handlebar forces and 0.3 and 0.5-0.6 for the pedal and hub forces, respectively. Thus, the relative contribution of the dynamic loading was much greater than the static loading at the handlebars but less so at the pedals and hubs. As indicated by the rainflow count, high amplitude loading was developed approaching 3 and 5 times the weight of the test subjects at the front and rear wheels, respectively. The power spectral densities showed that energy was concentrated in the band 0-50 Hz. Through stress computations and knowledge of material properties, the data can be used analytically to predict the fatigue life of important structural components such as those for steering. The data can also be used to develop a fatigue testing protocol for verifying analytical predictions of fatigue life.
为了提供用于预测越野自行车结构部件疲劳寿命及进行相关测试的数据，本文所述研究的目的是量化由路面引起的载荷输入到越野自行车上的情况。一辆完全配备仪器的测试自行车在踏板、车把和轮毂处安装了测力计，以测量通过自行车与骑行者及地面之间接触点作用的所有平面内结构载荷。一名站立的骑行者携带的便携式数据采集系统首次使得在长时间越野测试期间能够收集到这种载荷信息。总共有七名经验丰富的骑行者骑着测试自行车在一个下坡试验路段进行测试，测试自行车采用前悬架和全悬架两种配置。通过计算均值、标准差、幅值概率密度函数和功率谱密度函数，对载荷历史进行了定量描述，以表征载荷分量。对于站立姿势，垂直于地面的载荷分量的变异系数，车把力大于1.2，踏板力为0.3，轮毂力为0.5 - 0.6。因此，动态载荷在车把处的相对贡献远大于静态载荷，但在踏板和轮毂处则较小。如雨流计数所示，在前轮和后轮处分别出现了接近测试对象体重3倍和5倍的高幅值载荷。功率谱密度表明能量集中在0 - 50 Hz频段。通过应力计算和材料特性知识，这些数据可用于分析预测诸如转向部件等重要结构部件的疲劳寿命。这些数据还可用于制定疲劳测试方案，以验证疲劳寿命的分析预测结果。
