Cowrie pattern area is smaller than fast fracture area. Micromorphology shows that the fatigue striation is the main pattern. So it is the early fatigue fracture.

• 结果表明,断口宏观上有明显的贝纹线花样,贝纹区面积较小,而瞬断区面积很大,其微观形态主要为疲劳辉纹,因此泵轴的断裂属早期疲劳断裂。