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Repeated impact; carbon fibre; vinylester resin; residual stress; modulus; toughness; impact energy.

Two types of unidirectional carbon fibre, one of high strength (DHMS) and another of medium strength (VLMS) reinforced vinylester resin composites have been examined for their impact fatigue behaviour over 10⁴ impact cycles for the first time. The study was conducted using a pendulum type repeated impact apparatus specially designed and constructed for the purpose. A well-defined impact fatigue behaviour (S–N type curve) curve has been demonstrated. It showed a plateau region of 10–10² cycles immediately below the single cycle impact strength, followed by progressive endurance with decreasing impact loads, culminating in an endurance limit at about 71% and 85% of the single impact strength for DHMS-48 and VLMS-48, respectively. Analysis of the fractured surfaces revealed primary debonding, fibre breakage and pull-out at the tensile zone of the samples and a shear mode of fracture with breakage of fibre bundles at the compressive zone of the samples. The occurrence of a few major macrocracks in the matrix with fibre breakage at the high load–low endurance region and development of multiple microcracks in the matrix, coalescing and fibre breakage at the low-load–high endurance region have been inferred to explain the fatigue behaviour of the composites examined.

Rita Roy¹ B K Sarkar¹ A K Rana² N R Bose³

1. Department of Materials Science, Indian Association for the Cultivation of Science, 2A & B, Raja SC Mallick Road, Calcutta 700 032, India
2. Indian Jute Industries Research Association, Calcutta 700 088, India
3. Central Glass and Ceramic Research Institute, Calcutta 700 032, India

Published

February 2001

Manuscript received

24 July 2000

Manuscript revised

27 October 2000