Behavior of HDPE Geomembrane Sheet and Seams Subjected to a 90° Tensile Test

When a geomembrane seam specimen is tested in the peel mode, the material adjacent to the weld is bent at the same time as a tensile force is applied to it. As a result of bending, large and atypical stresses are imposed on the bent material; particularly at the outer fibers which is dependant on the thickness of the geomembrane. Initiation of failure at these outer fibers on relatively thick material may be anticipated. Clearly, the tensile strength with a material containing a 90° bend is less than a straight material with no bend. Also, when such failures occur total elongation of the specimen is low and debate continues as to the significance of low elongation values. Often the term "brittleness" of the undefined heat affected material adjacent to the weld is blamed. Using a custom-made 90° clamp, tensile tests have been conducted on unwelded geomembrane specimens. Results are then presented and compared with traditional peel test results. The correlation of a slightly offset 90° sheet tensile strength with a seam tested in peel (also 90°) is very interesting.