Dynamic Strength - Hybrid Anisotropic Materials for Wind Power Turbine Blades - page 142

where:
ΔT.is.the.change.in.temperature.and.t c ,.α c ,.and.E c .are.the.thickness,.thermal.
coeficient.of.expansion,.and.stiffness.respectively.of.the.constrain-
ing.plies;
t 2, .α 2, .E 2. are.the.thickness,.thermal.coeficient.of.expansion,.and.stiffness,.
respectively,.of.the.90°.piles.

This.stress.is.introduced.upon.cool.down.from.the.curing.temperature.due.
to.the.mismatch.in.the.coeficient.of.thermal.expansion.of.the.adjacent.piles.
in.a.laminate.
From.the.prediction.strength.of.every.layer,.we.can.approximate.the.aver-
age. strength. of. all. construction. and. answer. the. question. of. how. long. this.
construction.will.be.serviceable. 34
We.consider.that.every.layer.of.construction.has.strong.orthotropic.prop-
erties,. and. the. construction. has. a. homogeneous. structure. and. is. equally.
impregnated. by. epoxy. or. other. isotropic. resin.. Optimal. structure. has. ori-
ented.ibers.whose.direction.of.reinforcement.coincides.with.the.direction.of.
acting.normal.stresses.along.the.axis.x,.y,.z..(Figure 5.5).
Fatigue.strength.can.be.predicted.as.a.linear.correlation.between.compres-
sion.strength.and.the.function.Φ(σ),.see.Equation.(5.70).

σ -1 =σ s Φ(σ).. (5.70)

where:
.σ -1 .is.fatigue.strength.in.x,.y,.z.direction.
.σ s. is.compression.strength.in.x,.y,.z.direction.

Z

δz

δy

δx δx

δy

δz

X

Y

Fiber orientation in orthotropic composites.
Stress components coincide with fiber orientation X,Y,Z.

FIGURE 5.5
Fiber.orientation.in.orthotropic.composites..Stress.components.coincide.with.iber.orientation.
x,.y,.z..(From.Lethe,.De.Cuper.et.al..2009.. Journal of Mechanical Science and Technology .23.(4):.4..
With.permission.)