Hi,
the coefficients depend strongly on technology. Usually, K-factors are
given (relative change in resistance = K * strain). Here are some data:
p-Si: Kl = 25 (for NA = 10^19 cm-3)
      Kt = -5 (for NA = 10^19 cm-3)
n-Si: Kl = -25 (for NA = 10^19 cm-3)
      Kt = 3 (for NA = 10^20 cm-3)
English references are:
 Seto: Journal of Applied Physics. 47 (1976) 11, pp. 4780-4783
 Germer: Sensors and Actuators. 4 (1983), pp. 183-189
 Detry: Transducers'85. pp. 278-280
 Binder: Sensors and Actuators. 4 (1983), pp. 527-536
 Germer: Sensors and Actuators. 7 (1985), pp. 135-142
 French: Transucers'85. pp. 281-283
 Schubert: Sensors and Actuators. 11 (1987), pp. 145-155
More references are available in German.
With best regards,
Reinhard Buchhold