Pressurization methods using the pressurization buffer material such as rubber elastic body are hardly free from effects from deformation property of pressurization buffer material or deterioration in property of elasticity due to aging.This section describes a pressurization method using the pneumatic pressure.

(1)Pneumatic pressurization method and pressure profile

1)Pressurization method using pressure buffer material

・In the case of pressurization method using the pressure buffer material, the contact stress acts intensively upon the circumference edge area of the workpiece in the directions indicated by the red arrows, which in turn deforms the pressurization buffer material locally in the inner side of the edge. This results in a sudden reduction of contact stress in the adjacent side of the circumference (Fig. 1).

2）Pneumatic pressurization method

・Use of rubber expansion body much like a balloon which pressurizes the pressure buffer material section with the pneumatic pressure will make more consistent pressurization act on the workpiece based on the "Pascal's law" (Fig. 2).
・"Pascal's law" is a principle that when some force is applied to one point in the container with the fluid in it, contact stress with the same magnitude will impinge in the vertical direction of the surface of the container (Fig. 3).
・For durability of the rubber expansion body, it has to be at least 2 to 3 mm thick.This expansion body needs to be fixed to the pressurization plate without an air leak.
・The case of Fig. 2 can also be improved a good deal by selecting better rubber expansion body material, optimal condition, etc., even though a reduction of contact stress in the inner side of the edge area cannot be completely eliminated since intensive contact stress persists in the circumference edge of the workpiece.