Abstract
In this study, fatigue crack tests of CuNi2Si alloys using the replica technique under symmetrical tensile-compression loading, and rotational-bending loading were carried out with the same nominal stress amplitude. Observation and analysis results indicate that under different load types, the cracks display a trend of slow initiation growth and then rapid growth. The critical point is identified at the approximate value of 0.8 of the fatigue life fraction, and the crack growth rate of the sample under tensile-compression load is approximately an order of magnitude higher than that under rotational-bending load, resulting in the average life of the former being significantly shorter than the latter. Combining the observation results of the fractographical analysis and the surface-etched sample replica film, it can be seen that whether it is a tensile-compression load or a rotational-bending load, cracks mainly propagate in intergranular mode after initiation.
Highlights
Cu–Ni–Si alloy is a precipitation-strengthened copper alloy with good mechanical properties, fatigue, corrosion resistance [1] and electrical conductivity [2]
Before the point at which the life fraction is equal to 0.8, the crack length and crack growth rate are at low levels
The expansion rate of tensile and compression specimens is an order of magnitude greater than that of rotational-bending specimens
Summary
Cu–Ni–Si alloy is a precipitation-strengthened copper alloy with good mechanical properties, fatigue, corrosion resistance [1] and electrical conductivity [2]. It has been widely used for electrical components, such as electrical connectors, circuit breakers, relays and railway contact net positioning clamps, and rings [3,4]. It is necessary to study the fatigue fracture performance of CuNi2 Si alloy under various load types to provide a reference for related reliability and safety assessment. Yang et al [1] investigated the effects of specimens with and without cold working under both normal and salty atmospheric conditions on the fatigue properties and fracture behaviour of CuNi2 Si alloys under bending rotation. The specimens with cold working displayed shear mode fractures whereas those without cold working displayed normal mode fractures
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