We directly measured the stresses induced on impact between a golf ball and a golf club head. The strain sensors were embedded into grooves on the face of the club head. 3-axis strain sensors were able to measure one normal stress and two shear stresses at each location. The shear stress directions indicated by the outputs of the sensors agreed with the direction of the ball spin obtained from high speed camera images. The peak of the normal stress and shear stress on the contact face were measured to be 4×10^8 Pa and 1×10^8 Pa, respectively.

References :
Akira Hasegawa, Akihito Nakai, Eiji Iwase, Kiyoshi Matsumoto, Isao Shimoyama, “Measurement of the Impact Stress in a Golf Club Head,” IEEE 23rd International Conference on Micro Electro Mechanical Systems (MEMS '10), pp.592-595, Hong Kong, China, Jan. 25-28, 2010． [Proceedings]