That's called a stress riser. That's not a material problem, that's a design problem.the same problem happens with like materials, or even the same piece of material. On Sep 27, 2015 3:17 PM, "Jeff Scott via KRnet" <krnet at list.krnet.org> wrote:
> > > > > > > > has anyone combined fiberglass with carbon fiber > > >in their projects? For example the instrument panel, leading edge and > so on. > > +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ > > > > You are talking instrument panels here, generally a non structural > > component so it's not a big deal. However, the practice suggests a > > word of caution if done on other parts of the structure. Barnaby > > Wainfan has an article in the latest edition of "Kit Planes" were he > > cautions the use of combining materials of different strengths. For > > example, adding carbon fiber to wood components can actually make > > them weaker due to the different stiffness characteristics of the two > > materials. > > > > For example, a weight supported by two ropes, each rope carries half > > the load. Replace one rope with a wire and the wire carries the > > entire load until it breaks. The remaining one rope is not capable > > of carrying the load so it beaks. Read the entire article in the > > November 2015 issue of "Kit Planes". > > > > Larry Flesner > > Larry brings up a very good point here about mixing CF and other materials > in a structural environment. > > Caution, war story to follow... > I have a friend that decided to create Carbon Fiber tips on a wooden > prop. He trimmed down the wood prop tips a bit to make a more efficient > air foil, then wrapped the tips in carbon fiber to add strength. But > instead of tapering out the CF, the CF stopped abruptly roughly 30% of the > way in from the prop tips. After about 150 hrs in service, the prop failed > in flight. It shed one tip right at the edge of where the carbon fiber > started. The sudden imbalance cause the other tip to shed almost > instantly, but did leave the remains of the prop something close to > balanced. This was due to the stiffness of the CF causing the wood at the > edge of the CF to take on all of the bending moment of the prop tips. This > prop was in a pusher configuration on an Eze type aircraft. The departing > prop tips took the top 1/3 off one of the vertical stabs and tore off half > of one aileron as they departed the aircraft. The pilot was left with 70% > of his prop and a damaged aircraft at roughly 9500' in the mountains. It > took full throttle at now roughly 4000 rpm (estimated due to the 3500 rpm > limitation of his tach) out of his Lycoming engine to maintain flight, and > with the damaged wing and rudder, it took roughly 110kts to keep the plane > from rolling over. The pilot did make a safe landing at an airport. But > it was a hard lesson about mixing unlike materials in structural > application. > > Having said that, for some applications, glass is used as the core > material between layers of CF to make a very stiff composite section. But > engineering wise, the glass only counts as the sheer webbing and the CF has > to carry the loads. > > -Jeff Scott > Los Alamos, NM > > > _______________________________________________ > Search the KRnet Archives at http://tugantek.com/archmailv2-kr/search. > To UNsubscribe from KRnet, send a message to KRnet-leave at list.krnet.org > please see other KRnet info at http://www.krnet.org/info.html > see http://list.krnet.org/mailman/listinfo/krnet_list.krnet.org to change > options >
