StiReL (Stiffness Reduction of the Laminates) is a software tool for the analysis
of the composite laminates with damage. Symmetric
laminates containing 90layer in the middle can be
analyzed, such as [S/90_{n}]_{s} for example. Where
S is sublaminate with
complicated layup, it should be balanced laminate, like for
instance S = [+45/45]
or S = [+30/0/30], etc. In such laminates [S/90_{n}]_{s} loaded in axial
direction x, first damage that occurs is matrix
cracking in the middle layer or so called transverse
cracking. 

Due to this damage that accumulates with
increasing strain, stiffness of the laminate as well as
Poisson's Ratio are decreasing. In order to design composite
structures properly it is very important to know level at which its
elastic properties can drop due to damage.
StiReL is using algorithm for stress analysis based on
very well known models (such as Shear Lag, Hashin's etc.) initially
developed for crossply laminates and adopted for laminates with
more complicated outer layer layup.
Engineers and students can use StiReL as a design tool. It has
the following features:
 laminate contains 90layer in the middle and
sublaminate with complicated layup as an outer layer;
 uniaxial loading transverse to the 90layer is assumed;
 only constants of the UD composite and some parameters for
particular models are needed as input data;
 elastic constants of the laminate as well as of the
sublaminate are calculated;
 changes of the longitudinal Young's modulus and
Poisson's Ratio as a function of the crack
density in 90layer are calculated;
 six different models are available for prediction of
the stiffness degradation: three modifications of the Shear
Lag model, two variational models and model based
on FEA.
StiReL is designed for Windows™ and uses all advantages of its
graphical interface:
 attractive, efficient and easytouse interface;
 effective means for creating new sets of data, as well as storing,
browsing opening, and editing the existing sets of data;
 set of options that allows to configure data format, content of
report and screen options;
 builtin small text editor allowing to observe and compare the
results of various calculations in the text mode;
 data representation in text mode and in scientific graph mode;
 simultaneous output of experimental and predicted curves for
comparison.
Minimum hardware requirements:
 IBM PCcompatible computer, with 80486 processor or higher (it
should be able to run Windows 95/98/NT).
 VGA video adapter;
 3.25" FDD and HDD with approximately 1 Mb to install program and
store results.
