This set of Composite Materials Multiple Choice Questions & Answers (MCQs) focuses on “Static Mechanical Properties”.
1. Which static test is used to determine the tensile properties of flat composite laminates?
a) ASTM D7264
b) ASTM D3039
c) ASTM D3518
d) ASTM D4236
View Answer
Explanation: Tensile properties such as tensile modulus, tensile strength and Poisson’s ratio of flat composite laminates are determined using standard test method ASTM D3039. Straight-sided tensile specimens having constant cross-section are generally used for this test.
2. The end tabs in a tensile test specimen are made of a compliant and strain-compatible material.
a) True
b) False
View Answer
Explanation: The end tabs are adhesively bonded to the ends of the tensile specimen. The strain-compatible material is used at the end tabs in order to reduce the stress concentrations in the gripped area. It promotes tensile failure in the gage sections.
3. The tensile specimen is held in a testing machine by plane grips.
a) True
b) False
View Answer
Explanation: In tensile testing, the specimen is held by wedge action grips. The specimen is pulled at a recommended cross-head speed of 2 mm/min.
4. Which device is used to measure the different strains in a tensile testing specimen?
a) Electrical resistance strain gauges
b) Mechanical strain gauges
c) Optical strain gauges
d) Pneumatic strain gauges
View Answer
Explanation: An Electrical resistance strain gauge is used to measure the longitudinal and transverse strains in a tensile testing specimen. The device is bonded in the gage section of the specimen.
5. A tensile load creates both extension and shear deformations for an off-axis unidirectional specimen.
a) True
b) False
View Answer
Explanation: In an off-axis unidirectional specimen, the tensile load induces shear forces and bending couples, the specimen ends are constrained by the grips that create non-uniform S-shaped deformation in the specimen since its ends are constrained by the grips.
6. What causes the failure of unidirectional laminate specimens?
a) Interfacial shear failure
b) Matrix tensile rupture
c) Matrix shear failure
d) Longitudinal splitting
View Answer
Explanation: In the unidirectional laminates, the specimen fails by the longitudinal splitting parallel to the fibers. Longitudinal splitting is the de-bonding along the fiber-matrix interface which gives a typical broom-like appearance in the failed area of the specimens.
7. For off-axis specimens, the failure may occur by fiber-matrix shear failure.
a) True
b) False
View Answer
Explanation: The failure in off-axis specimens may occur by fiber-matrix interfacial shear failure, matrix tensile rupture and matrix shear failure. For these specimens, the tensile stress-strain curve may exhibit non-linearity.
8. Which fiber orientation angle of the laminas shows the maximum tensile modulus?
a) At θ=0°
b) At θ=30°
c) At θ=45°
d) At θ=90°
View Answer
Explanation: The tensile modulus and strength of a unidirectional specimen depends greatly on the fiber orientation angle(θ). The magnitude of these properties decreases with increasing fiber orientation angle. The minimum values of tensile strength and modulus are observed near 90° fiber orientation angle.
9. The fibers in a multidirectional laminate are in different fiber orientations.
a) True
b) False
View Answer
Explanation: The Tensile stress-strain curves for multidirectional laminates containing different fiber orientations are in nonlinear. A number of knee points are also observed in the stress-strain curve. The knee point is the point at which the two linear sections intersects.
10. What is the first knee point in a tensile stress-strain diagram?
a) First Knee Failure point
b) First Ply Failure point
c) First Fracture Failure point
d) Initial Knee Failure point
View Answer
Explanation: First Ply Failure (FPF) point has a great importance in laminate designs. For the laminates having high notch sensitivity, the failure occurs just after the First Ply Failure point. The cracks occurring at the FPF will lead to the possibility of fatigue failure as well as environmental damage.
Sanfoundry Global Education & Learning Series – Composite Materials.
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