Once all of the individual steps have been charted, then “what if” scenarios must be considered. What if it’s the wrong material? What if the process goes wrong? What if it doesn’t conform to expectations? You want to identify all the possible failure modes that could occur during the fabrication of the composite part and rank them in importance. In other words, rank them by the seriousness of the failure or defect of the part or process as compared to the expectation for that part or process.
The final step in determining what inspection methods and techniques are required is to graphically chart the information above, identifying the step-by-step process, failure points, degree of seriousness of the failure for the final part, inspection method for each part/process and the corrective action for identified failure.
There are two basic types of the defect measurement or identification – variable and attribute. Variable defects are those that can be measured, such as thickness, weight, width, length and physical strengths. Attributes are observations that are either present or not present, conforming or non-conforming. For example, if the specification for a part states that it must have gray primer, that’s classified as an attribute. The part either has or does not have gray primer. However, if the specification states that the part must have 3 to 5 mils of dry film gray primer, it would be classified as a variable. The primer must be measured to ensure conformity. These differences are important as the method and the technique for verification are established.
Any inspection plan must take into account the diverse market distribution for composite products. Inspection methods and techniques will vary according to the product and its intended use. A composite door that is used on a military armored vehicle will have very different critical characteristics than a door for a Class 8 truck. A nacelle that becomes part of an aircraft will have very different requirements than one used in the construction of a wind turbine assembly.
The inspection plan will identify the method or manner in which a specific inspection will be performed. If it is based on variable criteria, the method could define a test procedure or a method of measurement. Let’s take the example of the armored vehicle door panel: It will have certain ballistic requirements that will specify some destructive testing verification. By contrast, a door for a class 8 truck more likely will have a minimum and a maximum thickness requirement. In that case, the method would detail where and how the part thickness would be measured and what measurement tool would be used. The technique would detail the training required for proper use and repeatability of the measurement.