In the material strength test, stress and strain rate are often required to be constant. For example, during the cement quality inspection, the loading rate is required to be2.4 ± 0.2KN/S [1]; when measuring the upper and lower yielding points of metallic materials, the stain rate should stay between 0.00025/S and 0.0025/S; In the determination of elongation at break, the stress rate should stay in the range of 1-10N/mm2 S-1 when the elasticity modulus smaller than 150000 N/mm2 [2]. Since 1950s, Material Testing Machines, which adopted large-flow electro-hydraulic servo, valve to form control system, have appeared in developed countries. Control system of this type could meet the requirements for the stress and strain rate in the material strength test. For example, MTS and Instron from USA, Schench from German, and Shimadzu from Japan all adopted this type of system. With the improvement of the manufacturing level of proportional valve and the development of control technology, electro-hydraulic proportional valve began to be used as the main control part home and abroad [4]. However, this type of parts, which is vulnerable to pollution, requires medium of high cleanliness. It is of large noise and high price. This type of system could go wrong easily for the complex hydraulic system
DOI: 10.17762/ijritcc2321-8169.15017
