Microplane model M4

Implementation of Microplane model M4. This model is based on microplane concept. It describes the complex 3d behavior of material. However, the objectivity of model with regard to element size is unsolved - the parameters should be fitted for each element size. Since the stiffness matrix is not provided, a linear elastic is provided. This cause very slow convergence, when used in implicit codes. The model description and parameters are summarized in table 20.

Table 20: M4 - summary.

Description	M4 material model
Record Format	microplane_m4 nmp(in) # c3(rn) # c20(rn) # k1(rn) # k2(rn) # k3(rn) # k4(rn) # E(rn) # n(rn) #
Parameters	- nmp number of microplanes, supported values are 21, 28 and 61
	- n Poisson ratio
	- E Young modulus
	- c3,c20, k1, k2, k3, k4 model parameters
Supported modes	3dMat