performance of parallel computing is degrading with number of iteration?​??????????​?????

Dear Frnds

I am doing parallel computing using matlab (Parfor loop). I am writing FEM code for stiffness and stress calculation. When using coarse mesh, time is reduced to half(approx). But with fine mesh(more iteration). its performance is degrading.(sometime system hang or taking more time or out of memory error)

Desktop configuration: i7-3770 CPU@3.40GHz(4 core), RAM-8 GB,Window-64bit MATLAB: (R2014a)

Also i have used cell array for storing different variable size arrays(i know cell array take more memory but i dont know other options).With increasing no. of iteration size of cell array(used to store stiffness matrices) keep on increasing

plzzz help me, what should i do?????????? suggest me the possible corrections????