A study of fiber volume fraction effects in notched unidirectional SCS-6/Ti-15V-3Cr-3Al-3Sn composite. Ph. D. Thesis Final Report

Technical Report · Wed Sep 01 04:00:00 EDT 1993

OSTI ID:5446078

Covey, S J

Notched unidirectional SCS-6/Ti-15-3 composite of three different fiber volume fractions (vf = 0.15, 0.37, and 0.41) was investigated for various room temperature microstructural and material properties including: fatigue crack initiation, fatigue crack growth, and fracture toughness. While the matrix hardness is similar for all fiber volume fractions, the fiber/matrix interfacial shear strength and matrix residual stress increases with fiber volume fraction. The composite fatigue crack initiation stress is shown to be matrix controlled and occurs when the net maximum matrix stress approaches the endurance limit stress of the matrix. A model is presented which includes residual stresses and presents the composite initiation stress as a function of fiber volume fraction. This model predicts a maximum composite initiation stress at vf approximately 0.15 which agrees with the experimental data. The applied composite stress levels were increased as necessary for continued crack growth. The applied Delta(K) values at crack arrest increase with fiber volume fraction by an amount better approximated using an energy based formulation rather than when scaled linear with modulus. After crack arrest, the crack growth rate exponents for vf37 and vf41 were much lower and toughness much higher, when compared to the unreinforced matrix, because of the bridged region which parades with the propagating fatigue crack. However, the vf15 material exhibited a higher crack growth rate exponent and lower toughness than the unreinforced matrix because once the bridged fibers nearest the crack mouth broke, the stress redistribution broke all bridged fibers, leaving an unbridged crack. Degraded, unbridged behavior is modeled using the residual stress state in the matrix ahead of the crack tip.

• Research Organization: Cincinnati Univ., OH (United States)
• OSTI ID: 5446078
• Report Number(s): N-94-14769; NASA-CR--191165; E--8116; NAS--1.26:191165; CNN: NGT-40016; RTOP 510-01-50
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360603* -- Materials-- Properties
ALLOYS
ALUMINIUM ALLOYS
CALCULATION METHODS
CHROMIUM ALLOYS
CRACK PROPAGATION
FIBERS
FINITE ELEMENT METHOD
FRACTURE PROPERTIES
MATERIALS
MATRIX MATERIALS
MECHANICAL PROPERTIES
NUMERICAL SOLUTION
REINFORCED MATERIALS
TIN ALLOYS
TITANIUM ALLOYS
TITANIUM BASE ALLOYS
VANADIUM ALLOYS