筆記型電腦轉軸凸轂之可靠度分析

Abstract

在消費級電子產品的塑膠外殼設計中，凸轂(boss)扮演著重要的角色。在筆記型電腦中，用於固定螢幕轉軸的塑膠凸轂經常因長期反覆開闔，導致其使用的PC/ABS材料產生疲勞老化，使得材料性能下降並引發破壞，進而使筆記型電腦無法正常使用。一般而言，產業界通常以開闔25000次後是否發生破壞來作為螢幕轉軸處凸轂壽命的測試標準，其係模擬用戶三年後的使用狀況。若在開闔25000次後未發生破壞，即視為通過測試。然而，根據廠商統計資料，凸轂經使用三年後仍存在破壞的可能性。本研究假設筆記型電腦轉軸處之凸轂因電腦反覆開闔出現一裂縫，而後根據廠商提供之材料與應力資料，建構一套分析方法，評估該裂縫成長情形，並考慮影響裂紋成長各項參數的不確定性，運用機率理論結合力學破壞法則，評估轉軸凸轂經使用三年後之失效機率。分析結果顯示，失效機率與廠商統計之失效機率相近，證實本研究分析方法的適用性，可提供廠商參考。此外，本研究也比較不同PC/ABS材料比例對破壞機率帶來的影響，為未來選用材料的改進提供數據參考。

In the design of plastic enclosures for consumer electronic products, bosses play a crucial role. In laptops, the plastic bosses that secure the screen hinges frequently undergo fatigue degradation of the PC/ABS material due to repeated opening and closing over an extended period. This degradation results in a decline in material performance, eventually causing failure that prevents the laptop from functioning properly. Typically, the industry standard for testing the lifespan of these hinge bosses is to check whether any failure occurs after 25,000 cycles of opening and closing, which simulates approximately three years of user operation. If no failure occurs after 25,000 cycles, the boss is considered to have passed the test. However, according to manufacturers' statistical data, there is still a possibility of failure in the bosses after three years of use. This study assumes that a crack forms in the laptop hinge boss due to repeated opening and closing of the laptop. Based on the material and stress data provided by the manufacturer, an analytical method is developed to assess the growth of this crack while considering the uncertainties in various parameters that affect crack growth. Using probabilistic theory combined with fracture mechanics, the failure probability of the hinge boss after three years of use is evaluated. The analysis results show that the estimated failure probability closely matches the failure rate observed in manufacturer statistics, demonstrating the applicability of the proposed analytical method as a reference for manufacturers. Additionally, this study compares the effects of different PC/ABS material ratios on failure probability, providing data for improving future material selection.