Environmental Engineering Reference
In-Depth Information
vibration..If.the.frequency.is.1,000.cycles.per.minute,.the.internal.heat.of.the.
sample.will.be.50.to.70°C.
If. the. frequency. decreases. to. 300. cycles. per. minute,. the. internal. heat.
simultaneously.is.reduced.to.25.to.30°C..The.very.important.characteristic.
of.dynamic.properties.is.the.internal.dispersion.of.energy.(critical.damp-
ing.coeficient).
36
.During.the.harmonic.vibration,.which.can.reach.1.×.10
6
.
cycles,.there.is.no.visible.cracking..It.does.not.mean.that.there.is.no.inter-
nal.cracking.
It. is. very. important. to. use. nondestructive. ultrasonic. evaluation. for. the.
determination.of.the.dynamic.modulus.of.elasticity,
37
.and.not.visible.crack-
ing.propagation.
The. criteria. of. quality. for. dynamic. fatigue. after. 1. ×. 10
6
. to. 5. ×. 10
6
. cycles.
have.shown.crack.visibility..However,.the.samples.with.visibility.cracks.after.
testing.have.very.high.strength.characteristics..Therefore,.the.value.of.pre-
dicting.fatigue.strength.is.somewhat.lower.than.test.results.
Correlation.between.dynamic.fatigue.and.the.number.of.cycles.in.the.case.
of.harmonic.bending.in.the.graphite/epoxy.composites.exist.
5.8.4
Experimental Investigation
Researchers. did. between. 5. to. 20. tests. on. small. specimens. generating. the.
fatigue. strength.
35
. The. diagram. describing. the. relations. between. loading.
and.number.of.cycles.has.a.name:.Wohler.diagram.(Figure 5.7)
Table 5.3.represents.the.parameters.of.the.compression.strength.for.graph-
ite/epoxy. composites.
36
. We. tested. six. samples. and. determined. the. sample.
standard.deviations.
Also,.we.determined.three.parameters:.t,.probability.P(t).using.tabulating.
function.(Table 5.4),.and.function.Φ(σ).following.Equation.(5.71).
Fatigue. strength. prediction. has. a. good. correlated. with. compression.
strength.(Figure 5.8).
Table 5.5. represents. the. parameters. of. interlaminar. shear. strength. for.
graphite/epoxy.composites..We.tested.six.samples.and.determined.the.sam-
ple.standard.deviation.
Also,.we.determined.three.parameters:.t
1
,.probability.P(t
1
).using.tabulating.
function.(Table 5.4),.and.function.Φ(τ).following.Equation.(5.84).
Fatigue. strength. prediction. using. Laplacian. function. Equation. (5.88). is.
represented.in.Table 5.6.
Tabulating.Laplacian.functions.are.given.in.Table 5.7.
The.number.of.samples.N,.the.sample.mean.σ
bm,.
τ
bm
,.and.sample.standard.
deviation.Sj.and.Sτ.was.selected.from.the.pooled.data..The.normal.distribu-
tion. B-basis. and. A-basis. allowable. was. calculated. using. the. pooled. mean,.
standard.deviation,.and.tolerance.factors.for.each.environment.
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