ebarbero's blog

When using CZM for crack propagation, for each CZM element, once the separation delta > delta_c, the adhesive is completely damaged, cannot transmit stress. delta_c is the separation on the right side of the bilinear or trapezoidal models. How can I get the length of the crack for each increment of applied displacement or load? I can see that the totally damage element disappear from the Visualization but I need a better way that gives me crack length, not just a picture that shows the crack longer for each increment.

p. 1426, last par., should read (revision in [brackets]): "Satin weaves are depicted on Figs. 1c, 3d and e, again with the fills horizontal and the warps vertical. A [satin] is generated by..."
See also http://dx.doi.org/10.1016/j.compstruct.2010.11.014
and http://dx.doi.org/10.1016/j.compstruct.2010.11.016

The longitudinal compression strength of unidirectional composites F1c, also called Xc, is very difficul to test for, so often you don't have the value for the particular material (fiber, matrix, volume fraction) that you wish to use. Further, just having data does not tell you what paramaters really influence its value--it is not the compressive strength of the fiber, I can assure you. So, there is a simple formula that you can use to predict its value and also to understand what are the parameters that really affect the compression strength of the composite.

The PDA model implemented in Abaus is an implementation of the idea of the cohesive zone model (CZM), which is quite popular for the analysis of delaminations, but PDA is for intralaminar damage. The problem my group faced when trying to use PDA was "where do we get the material parameters?"  We asked around in blogs and such but could not find a definitive answer. So, we went to work and came up with a methodology that may serve you.

New textbook includes an explanation of the concepts involved in the detailed analysis of composites, a sound explanation of the mechanics needed to translate those concepts into a mathematical representation of the physical reality, and a detailed explanation of the solution of the resulting boundary value problems by using commercial Finite Element Analysis software such as Abaqus.

A discrete damage mechanics (DDM) model is now available as a UGENS/UMAT implementation for Abaqus/standard. This is an analytic constitutive model for laminates composites, based on discrete fracture mechanics. It is capable of predicting matrix crack initiation and crack density evolution using just two parameters--the critical energy release rates (ERR) in opening mode I and shear mode II. A methodology is available to determine those (invariant) material properties from experiments.