http://www.mif.pg.gda.pl/kft/Akron/ch4-Mechanical-Properties-of-Wood.pdfThis is a great paper that covers a lot of the questions that bowyers have about why bad things happen to otherwise good bows.
excerpt:
Elasticity implies that deformations produced by low stress
are completely recoverable after loads are removed. When
loaded to higher stress levels, plastic deformation or failure
occurs. Bows taking set or blowing up.
Contents
Orthotropic Nature of Wood 4–1
Elastic Properties 4–2
Modulus of Elasticity 4–2
Poisson’s Ratio 4–2
Modulus of Rigidity 4–3
Strength Properties 4–3
Common Properties 4–3
Less Common Properties 4–24
Vibration Properties 4–25
Speed of Sound 4–25
Internal Friction 4–26
Mechanical Properties of Clear Straight-Grained Wood 4–26
Natural Characteristics Affecting Mechanical Properties 4–27
Specific Gravity 4–27
Knots 4–27
Slope of Grain 4–28
Annual Ring Orientation 4–30
Reaction Wood 4–31
Juvenile Wood 4–32
Compression Failures 4–33
Pitch Pockets 4–33
Bird Peck 4–33
Extractives 4–33
Properties of Timber From Dead Trees 4–33
Effects of Manufacturing and Service Environments 4–34
Moisture Content 4–34
Temperature 4–35
Time Under Load 4–37
Aging 4–41
Exposure to Chemicals 4–41
Chemical Treatment 4–41
Nuclear Radiation 4–43
Mold and Stain Fungi 4–43
Decay 4–43
Insect Damage 4–43
References 4–44
