View non-flash version
www.sname.org/sname/mt April 2013 are analyzed using matrix algebra. Analysis of composite laminates using CLT grew popular as personal comput- ers became more common in the 1980s. CLT still forms the basis of most laminate analysis software today but gener- ally only considers panel structures. Finite element analysis (FEA) for complex marine struc- tures is an accepted tool to determine stress levels and areas of stress concentration that require des ign refinement. Using FEA for composites highlights the need to move from 2D shell elements to 3D layered solid elements. As-built ply stiness and strength characteristics need to be known in a 3-axis system, and details such as joints and ply drop-os need to be modeled with sucient delity. Because composites are non-homogeneous, layered structures, failure cannot always be accurately predicted using linear FEA methods. Current state-of-the-art pro- poses the use of multicontinuum theory (MCT) algorithms to decompose lamina (ply) stress/strain elds down to the ber and matrix (resin) level. is level of detail is suitable for a relatively simple structure, such as a bicycle frame, that will be manufactured in quantity. High performance structures engineered on the edge of catastrophic failure, such as Americas Cup yachts, also warrant this detailed FEA approach. However, the design of geometrically com- plex marine structures for everyday use may not warrant complex models with billions of elements that may need to be run on supercomputers. A move towards standard manufacturing, joining, and detail designs will help to ensure the validity of even the more basic nite element models. A key element here is verication that as-built marine structures behave as pre- dicted, which can only be conrmed with full-scale testing and at-sea experience. Process control Process control for marine composites manufacturing took a quantum leap forward with the advent of resin infusion. e process produces laminates with very predictable ber- to-resin ratios and virtually no voids. Gone are the days when a worker may have applied too much resin in one area or too little in parts of the mold that were dicult to access. However, resin infusion is not infallible: Air leaks in the vacuum bag can introduce voids; corner details can create bridging or reinforcement wrinkling; and the work- ing time of resin before it cures may be too short to wet-out the entire part. Trained quality assurance (QA) personnel can detect most of these problems before the actual infu- sion takes place, which is more realistic than having a QA person continuously looking over the shoulder of a lami- nator during hand layup operations. The Seabreacher X can sustain high-speed dives and then breach the surface, launching the entire vessel clear out of the water. The unique personal watercraft uses a hand-laid composite, monocoque structure built by Rob Innes and Dan Piazza of Innespace Productions in New Zealand. ?E Ú ±¼ Ø ±,5Ex? ±,, ^ ås üEs mance marine laminates use sandwich construction.