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Geogrid tensile strength at low strains is difficult to determine due to the non-linear, viscoelastic behavior of thermoplastic polymers. Their response to applied tensile loads is profoundly different from that of elastic materials including elastic structural metals. The stress-strain properties of plastics are not constant, varying greatly and nonlinearly with the test parameters. Therefore, if testing conditions are not controlled and accounted for, they can be inaccurate predictors of tensile performance. The measurement of tensile modulus is affected by such factors as temperature, sample length, gauge length, extension rate, and tension and strain measuring equipment.
It is not easy to define the effect of the numerous variables involved with the tensile testing of thermoplastic materials. However, the general effect of a few of the more important and controversial variables was investigated in order to provide some appreciation of the sources of variability. This paper presents the results and observations from an inter-laboratory study that determined tensile modulus of stiff polypropylene geogrids. Various test parameters and procedures affecting the measured results and their potential relevance to field performance were studied. Conclusions and guidelines are provided, and recommendations are made for modifications to current test methods when tensile modulus at low strains is of particular interest.
geogrid, polypropylene, tensile, extensometer, modulus, single rib, reinforcement, soil
Products Engineer, TENAX Corporation, Jessup, MD
Geosynthetic Application Manager, Titan Geosynthetics Co., Ltd., Taipei,
Program Manager, Geosynthetics Technology, TRI/Environmental, Inc., Austin, TX