2. Picture Frame Test:

The picture frame test is another method for shear testing of composites. This method is mainly used for the shear testing of woven composites.

A picture frame fixture for shear testing is sketched in Figure 8.16. The frame has four legs which are hinged to form a picture frame. Further, there is a rod which runs across one of the diagonal of the frame. It should be noted that this rod is not in the plane of the frame but runs behind the frame. The lower end of the rod is hinged with the common hinge of the two legs meeting in that corner. The other opposite corner hinge is resting in the slot provided in the rod. Further, at the lower end the rod is again hinged to individual legs of the frame. The lower end of the rod is fixed in jaws of the loading machine. Thus, when the load is applied through the upper end of the rod, it pushes these two legs apart and deforms the frame. These two legs in turn push their adjacent legs making their common hinge to slide in the slot of the rod. The plate deforms into a diamond shape. The woven composite is clamped to the frame with the help of clamping plates.

The pre-treatment of specimen is essential in this testing. The pre-treatment is given in the following paragraphs.

The specimen is pre-sheared several times before experiment, so as to make the yarns, as well as their intervals, more uniform hence obtaining a more consistent geometry of the whole fabric. When clamped into the fixture, the specimen is kept exactly loose in order to avoid pre-tension in both two directions of yarn. Beforehand, several marks are drawn on the contacting point of fixture and specimen; then after the test, it can be ensured by observation that the marks are still contacted; therefore, there is no slippage between the specimen and the clamping plates.