EFFECTS OF GAUGE LENGTH AND STRESS-CONCENTRATION ON THE COMPRESSIVE STRENGTH OF A UNIDIRECTIONAL CFRP

Compression tests for a unidirectional CFRP were carried out for a wid e range of gage lengths, three different configurations of end tab edg es and two different end tab materials under the conditions of constan t specimen thickness. The relation of sigma(c) - L is to be divided in to two parts, namely, a part where the compressive strength, sigma(c), is nearly constant independent of gage length, L, and beyond that, a part where sigma(c),decreases with increasing L. The apparent compress ive strength measured by Celanese test method was lower than the true compressive strength because of the stress concentration near the end tab edges of the specimen. The true compressive strength was obtained by using the specimen where the gage lengths of 3.2 mm and 6.4 mm, and the material of end tab is stainless steel.