What is the big idea?
Current composite design is nearly 100% empirical. In aerospace, the building block process requires thousands (or hundreds of thousands) of tests of increasing complexity, from simple laminate coupons to structural elements, to details to components to full-scale test, to develop the design space. Design is constricted by what laminates have been tested. Exploring new design concepts or materials isn’t feasible because of the testing required.
We propose to allow you to break out of the restrictive building block process by using analysis to examine the constituent materials (i.e. fiber and matrix) independently, and find where the onset of failure in the material occurs; hence the name, Onset Analysis. When does my matrix start to become critical? When does my fiber become critical? When (and where) is a delamination likely to start? When will the fiber overcome shear-lag and start to unload? Those are the critical questions in design that Onset Analysis can answer, for any layup, any geometry, without a mountain of test data.
Onset Analysis also enables you to look at your design under extreme environments, like elevated temperatures, moisture, cold dry, or even the extreme cold of space applications.
How is this different from other composite methods I’ve heard of?
Other failure criteria you’ve heard of, such as Hashin or Tsai-Hill, or Tsai-Wu or others, assume that a ply is a homogeneous material, and ignore the fact that there are fibers in a matrix and out-of-plane loads. They’re engineering approximations; curve fits of specific ply failure tests that create a failure envelope.
Onset Analysis is actually a throwback to a classical way of doing things. It’s essentially the von Mises approach, evolved and adapted for composites. In Onset, we separate the strains in the fiber and matrix, looking at the full 3D state of strain, and evaluate them independently.
So are you using damage progression?
No. Onset Analysis is not a damage progression approach. From a design standpoint, if your material has failed prior to its target load, the design has failed. Why go further?
The methodology looks for the beginnings, the onset, of failure in the material as a design criteria instead of catastrophic failure. Of course in composite design, it would be impractical (and unnecessarily limiting) to design to the first microscopic critical value, so our analysis can also look for the initiation of higher order events, like fiber unloading, initiation of delaminations or even estimates of laminate unloading. All of this without damage progression.
What kinds of problems can Onset Analysis address?
Onset Analysis can be used to evaluate static strength of composite details including bolted-joints, bearing, bearing-bypass, and especially matrix dominant problems like bonded-joints and bonded repairs. It is the only current method that can accurately assess matrix issues.
The method can also be used to look at problems like compression after impact (CAI), and fatigue.
Do you have tools I can try out now?
No yet. We’re developing our tools as we speak, but that’s one reason we need to talk to you. You can help us shape our tools and ensure that they work for your specific