抄録
For testing the complete deformation characteristics of brittle materials such as rocks and concrete, a stiff testing machine should be employed, and the compressive force acting on a specimen should be preferably controlled by the rate of strain in the specimen. The authors firstly designed and constructed a uni-axial compressive testing machine of oil pressure type controlled automatically and accurately by the rate of strain by using a servo-control system.
Secondly, performance of this machine was examined by testing specimens of concrete with various brittleness. The tests show that merely by this control system the apparent stiffness of the machine nearly equal to the brittleness factor of the specimen can be adjusted up to 90t/mm. For specimens with higher brittleness factors, up to 140t/mm, satisfactory results can be obtained by adopting stiff columns which are subjected to compression together with specimens.
It is also proved that the rate of deformation can be controlled smoothly from 0.001 to 2mm/min for specimens with the total deformations of about 2mm, and from 0.0025 to 0.5mm/min for specimens with those of about 0.5mm. Thus, the complete stress-strain diagram of concrete can be obtained under the strain rate from 1×10-6/sec to 140×10-6/sec, even for high strength concrete of high brittleness.
It is found that the Young's modulus, the compressive strength and the brittleness factor of concrete increase with increasing the rate of strain, while the strain corresponding to the maximum stress decreases, and that among ordinary concrete, lightweight aggregate concrete and mortar, the brittleness of the third is greatest, and that of the second is greater than that of the first.
