The required stiffness of a section of a composites part depends upon the overall design and service expectations.  Several factors, including the life expectancy of the object, the load rating of the composites surface, the inter-laminar bond strength, will help determine the threshold requirements.  Testing is very important to determine the life expectancy of the part and whether it meets the requirements of its’ job.

Panel stiffness can be modified to meet these requirements using two basic methods.  One way to increase the stiffness of an unsupported composites panel is to reduce the size of the panel through additional support structures.  The other way is to increase the panel thickness across the same area.  Choosing which method to use depends upon the engineering of the part and determining which method is acceptable with the surrounding part layout.  If there is room to add supports, this is likely a quick and easy option.  If there is room to increase the thickness, adding new or additional coring materials may be a simple solution.

Building a strong and stiff composites structure can be accomplished with the extremes of  building a robust “skeleton” with small open areas and a thin skin, or having a basic, limited “skeleton” with a heavy duty cored laminate that supports itself.

A combination of the two usually works out best.

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There of course are several ways to go about building a basic structure to use for the basic shape.  This video gave lots of good ideas and examples of materials that are relatively inexpensive.

The second part of the video shows some of the actual fiberglass work.  This video of less than eight minutes does not nearly do justice to the amount of work and effort that went into finishing this project!  It was great that the author documented his work and shared with all.  This was a major project that is not for the faint of heart.

He does a very good job explaining the process and materials used in this construction. Every project is unique, however. When discussing the thickness of the fiberglass skin, there are many variables that determine the finished strength. The number of layers to use is dependent on the amount of underlying support structures, part geometry, and required load bearing capacity of the structure. Some areas may need to be stronger for impact resistance and structural loads.

The video author discusses only using epoxy resin with Styrofoam as opposed to polyester resin which will react with the Styrofoam.  Polyester resin can be used if separated from the Styrofoam with an additional layer.  While I have only seen it advertised, there are new spray on primer materials available to cover the Styrofoam and allow polyester resins to be utilized afterward.

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