This set of Composite Materials Multiple Choice Questions & Answers (MCQs) focuses on “Static Mechanical Properties – Set 2”.
1. In angle ply laminates, the softening effect is observed for the smaller fiber orientation angle(θ).
a) True
b) False
View Answer
Explanation: In angle ply laminates, the softening effect is observed for the larger fiber orientation angle(θ). As a result of this the modulus decreases with the increase in the load. The softening effect is attributed to the shear stresses.
2. The modulus increases with load due to the stiffening effect in angle ply laminates.
a) True
b) False
View Answer
Explanation: The stiffening effect is observed for smaller fiber orientation angles(θ). It causes an increase in modulus with increasing load. This effect is attributed to the longitudinal tensile stresses.
3. The lamina stacking sequence has a great influence in failure modes of multidirectional laminates.
a) True
b) False
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Explanation: For the multidirectional laminates containing laminas of different fiber orientations, the tensile failure mode and tensile strength are strongly influenced by the lamina stacking sequence. Transverse cracking, delamination, longitudinal cracking are some of the damages that occur in the laminates which will lead to the composite failure.
4. The tensile strength and modulus of a woven fabric laminate are higher than multilayered laminates.
a) True
b) False
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Explanation: The tensile strength and modulus of a woven fabric laminate are lower than multi-layered laminates. The primary reason for their lower tensile strength and modulus is the presence of fiber undulation in woven fabrics. These crimped fibers have a tendency to straighten out, which generates high stresses in the matrix
5. Which is not a factor controlling the tensile properties of woven fabric laminates?
a) Number of fiber ends
b) Lamination pattern
c) Fabric style
d) Manufacturing time
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Explanation: The tensile properties of woven fabrics can be controlled by altering the yarn characteristics such as number of fiber ends, amount of twist in the yarn etc. The tensile properties can be also varied by changing lamination patterns such as parallel lamination, cross lamination etc and the fabric styles.
6. The 10° off-axis test is used to determine flexural properties of a composite.
a) True
b) False
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Explanation: The 10° off-axis test is used to determine the in-plane shear properties of a composite. It involves uniaxial tensile testing of a unidirectional laminate with fibers oriented at 10° from the tensile loading direction.
7. What is the most common failure mode at the fiber orientation angle 90°?
a) Fiber failure
b) Longitudinal splitting
c) Matrix tensile cracking
d) Fiber–matrix interfacial shear failure
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Explanation: The macroscopic failure modes vary in different fiber orientation angles. The fiber failure and longitudinal splitting occurs at 0° fiber orientation angle and for the intermediate angles(0<θ<90), a combination of matrix tensile cracking and fiber-matrix interfacial shear failure are observed.
8. Which type of laminate contains separate layers of both low and high elongation fibers in a common matrix?
a) Woven fabric laminates
b) Multidirectional laminates
c) Inter-ply hybrid laminates
d) Cross-ply laminates
View Answer
Explanation: In Inter-ply hybrid laminates, two or more fibers of different elongations are incorporated within a single matrix. Low-elongation fibers like high-modulus carbon fibers and High-elongation fibers like Kevlar-49 are sometimes incorporated into a single matrix. These composites exhibit much higher tensile strain at failure than the low-elongation fiber composites
9. The tensile modulus values of the interply hybrid laminate are between that of the low elongation and high elongation fiber composites.
a) True
b) False
View Answer
Explanation: The major advantage of the interply hybrid laminates over the low-elongation fiber composites are the enhanced strain-to-failure when subjected to tensile loading. It is because of the higher tensile modulus value of interply hybrid laminates.
10. Which is not a test used for determining the compressive properties of a specimen?
a) Celanese test
b) IITRI test
c) Sandwich edgewise compression test
d) Coupon test
View Answer
Explanation: Compressive properties of composite laminates are difficult to measure due to sidewise buckling of specimens. Celanese test, IITRI test and Sandwich edgewise compression test are some of the important tests to determine the compressive properties of thin composite laminas, whereas coupon testing is used to determine static and dynamic material properties of composites.
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