Method and Apparatus for Testing Fiber Reinforced Plastic Laminates

The present invention relates to a test apparatus and particularly to an inexpensive apparatus for applying a bending load to a fiber reinforced plastic laminate. In the development of fiber reinforced plastic laminates for various uses, particularly automotive uses, it is desirable to accumulate data relating to the response of the laminates under various conditions. This is particularly important when laminates are used for spring components on automotive vehicles, particularly trucks and the like. It can be appreciated that laminates used in springs are subjected to bending loads under varying temperature and humidity conditions. Thus, it is important to know the response of various laminates under varying bending loads and atmospheric conditions.

Obviously, it is impossible to construct full size springs if a large number of various combinations of fibers and plastics are to be tested. The various combinations of fiber and plastic can be molded in small inexpensive test specimens. While it is possible to test the molded specimens in presently available test equipment, the equipment is rather large and cumbersome. The large size of the equipment does not lend itself to use in controlled atmospheric conditions or in the testing of a large number of specimens. Also, it is impossible to measure the weight gain of a specimen as a result of moisture adsorption because of the size of the equipment.

The present invention provides an apparatus for retaining a test specimen and applying a bending load to the specimen. In particular, the apparatus is a relatively light weight metal frame that permits testing of the specimen under any humidity and temperature conditions. The moisture absorption of the test specimen can usually be determined by merely weighing the combination of the apparatus and specimen before and after the tests since the frame is comparable in weight to the weight of the specimen. The frame has an arcuate shape with the ends bent towards the center to retain the specimen. Normally, the test specimen will consist of a relatively thin elongated strip of the laminate. The bending load is applied to the center of the test specimen by a combination of a screw member and a threaded opening in the top of the arcuate shaped portion of the frame.

The combination of the test specimen and apparatus can be placed in autoclaves or similar devices where the temperature and humidity may be controlled at desired levels. Normally, the test specimen will be subjected to relatively high temperatures, for example 175.degree. F., under relatively high humidity, i.e., more than 90 percent humidity. Under these conditions most laminates absorb considerable moisture which results in their early deterioration. Obviously, materials that are to be used in automotive components must be capable of withstanding considerable moisture and temperature without failure. Under normal conditions the flexing of a spring will produce temperatures in the laminate that are considerably higher than atmospheric temperatures.

The present invention will be more easily understood from the following description when taken in conjunction with the attached drawing in which:

The sole FIGURE shows a pictorial view of the apparatus with a test specimen of a laminate installed therein.

Referring to the drawing, there is shown an apparatus suitable for holding an elongated test specimen of fiber reinforced plastic laminate and applying a bending load thereto. The apparatus comprises an arcuate shaped frame member 10 which is preferably formed of steel or a similar metal. The ends 11 of the frame member are bent inwardly towards the center of the member to provide a lip for supporting the ends of the test specimen 12. The bending load is applied to the test specimen by means of a bearing plate 13 which rests on the test specimen and a screw member 14. The screw member 14 threads through a threaded opening 15 in the arcuate shaped member and the bending stress imposed on the test member is controlled by the position of the screw member. Suitable tubular members 20 are secured to the ends of the arcuate shaped member to prevent the apparatus from rolling over during a test procedure.

Normally, the test specimen 12 will be approximately one inch wide by five inches long, and the frame member should be sized accordingly. A number of test specimens are placed in suitable holders and the group is placed in a controlled atmosphere, for example, an autoclave or similar device. The chamber should have means for controlling not only its temperature but its humidity. It has been found that if the temperature is raised to approximately 175 degrees and the humidity is at least 95 percent, results will be obtained that permit one to eliminate or discard those laminates which are unsatisfactory. After suitable laminate candidates have been selected, further and more exhaustive tests can then be carried out. The amount of moisture absorbed by the test specimens is easily determined by weighing the test specimen and sample holder prior to the beginning of the test and after completion of the test. The amount of moisture absorbed by a specimen is an important consideration in designing laminates for automotive components. Mositure adsorption is one factor in the failure of reinforced plastic laminates.