I am a PhD student on Timber structure.I have modelled timber beam using solid 45 element as 4 points bending but my result is overestimated.I have reviewed the literature and I have found that assigning Tsai_Wu failure mode in timber can solve the problem.I have found Tsai-Wu in following category in Ansys 12.1:Material model/nonlinear/inelastic/non metal plasticity/failure criteria/criteria3But Ansys appears the following error:*** ERROR ***                           CP =       2.891   TIME= 16:56:04 Failure criteria input values for signs on stresses for material 1 are   not correct.       Please find the picture and log file as further informatuion on input data.Any help on assigning Tsai-Wu and How to model timber material (bending test) in Ansys would be highly appreciated.