Mechanical properties of covering materials for greenhouses .2. Quality assessment

The mechanical behaviour of the covering materials of greenhouses may be assessed by means of conventional and specific testing methods. No standard methods exist for testing the mechanical and physical properties of flexible and rigid plastics and glass to be used as covering materials of greenhouses in the European Union (EU). Some of these properties, are rather specific for greenhouse applications and cannot be measured properly with existing testing methods. This situation becomes even more complicated because of the different requirements and climatic conditions of the various EU regions. This paper provides a systematic presentation of the mechanical properties measured by existing ''general purpose'' methods as well as specific testing methods included in national and international standards. The values presented are found to vary considerably for the same material and they also differ between the different materials considered, with the difference depending on the testing method used. In general, technical information regarding the mechanical properties of materials used as coverings of greenhouses is neither available nor warranted in a systematic way with a few exceptions. This work is intended to improve the current knowledge for accessing and defining the quality criteria for evaluating the variety of greenhouse covering materials encountered in EU countries. (C) 1997 Silsoe Research Institute.