Mechanical Properties of FRP

The Effects of the Base Materials in Each Layers of GRP

Abstract

Glass fiber reinforced polyester laminates (GRP) have recently found a wide industrial application and the mechanical properties of the laminates have often been reported. However, few are really studied based on a well-organized experimental method.
The purpose of our investigations is to study the following effects using the orthogonal array table type L₈₁.
(1) The effects of the kinds of base materials in each layers on mechanical properties of GRP.
(2) The effects of the molding conditions on mechanical properties of GRP.
The test samples were prepared by the hand lay-up molding method with three kinds of base materials which are shown in Table I and Fig. 3.
Using the test pieces from the samples, tensile strength, tensile modulus, flexural strength, flexural modulus and thickness were measured in the atmosphere of 20±°C, 65±2% R.H. and the following results were obtained.
(1) The force applied to a tensile test piece seems to be uniformly distributed into each layer of the laminates.
(2) When the laminates is used as a bent member, the effects of the kinds of base materials are scarcely influenced by the adjacent base materials, and the farther the base material is located from the central layer, the larger become the effects. In ten plies of laminate, the effects of the kinds of the interior four base materials can be neglected.
(3) It is advisable not to use woven roving on compression side of bent members.
(4) The slower the rate of resin curring is, the stronger products can be obtained.
(5) Differences of breaking stresses and moduli are not noticeable between the samples molded by the man of experience and one of inexperience.
(6) The screw roller brought a good result in lamination of satin-like weavings, and mohair and wool rollers brought good results in lamination and resin impregnation of the woven rovings. The washer roller gave only bad result for all base materials.
(7) After-curring of the sample caused lower tensile strength and modulus with higher flexural strength and modulus. After-curring of the test pieces subsequent to machining caused higher strength and modulus than curring prior to machining.
(8) Wider specimens improve apparent breaking stress and modulus.