Dumbell type test specimen has been proposed in the literature[5] for finding out the strength of plastic sheets with no mention about the testing of the joint strengths in welds. Dumbell type specimen as shown in Fig. 13.5, has been used for testing the strengths of the parent plate as well as that of the butt welded specimen by some investigators. End effects can be avoided by removing and discarding a strip 35 mm wide from both the sides of the welded test piece. These test specimen can be tested on a 20 tonne universal testing machine using flat grips and 2 tonne scale. The smoothness of the test specimen, which is inherent in the rigid P. V.C. sheet, may render the gripping difficult in the flat jaws. Tight and strong grips can be obtained by making cerrations on both the sides of the specimen near the ends.

Straight test pieces are used for testing the strengths of double strap fillet joints, as shown in Fig. 13.6. The testing procedure is the same as in the case of butt welded joints.