Analysis of stress relaxation and data acquisition in the Compression Process of Herbage Materials

in order to obtain rheological properties such as the mechanical property, stress relaxation and creep in the Compression Process of Herbage Materials, based on the compression test platform of herbage materials, the virtual instrument system is constructed by using software Labview and NI data acquisition card. This system can collect compressive force, compressive force of test platform wall and deformation of herbage materials and so on during compression process, and can process all data in real time. Taking alfalfa as experimental materiel, stress relation experiments are conducted on baling test platform in five different sections, which has posted that stress relaxation curves of compressed alfalfa piece have same character in different sections, i.e. the stress sharply reduce in the initial period and change slowly in the later period. Meanwhile, the initial stress is more and the stress after relaxing is more. The viewpoint of choosing compression frequency by stress relaxation ratio is educed, and it suggests that compression frequency of baler shouldn't be too high. Compression frequency can be chosen lower if initial density is bigger. Therefore the aims of reducing energy consumption, ensuring productivity and stable product quality can be achieved.