Dynamic tests were carried out on plain weave carbon epoxy composite plates of different thicknesses, namely, 12, 16, and 24 layers (0.21mm∕layer) using a Penetrating Split Hopkinson Pressure Bar (P-SHPB). Protruding spherical penetrators of different sizes (3/16, 7/32 and 1/4-in.) were used to determine the perforation threshold energies for each woven specimen. The specimen damage thresholds considered in this paper are: below perforation limit (BPL), at perforation limit (PL), and above perforation limit (APL). Perforation limits (energy that must be exceeded to perforate or completely penetrate the specimen) were experimentally determined using P-SHPB. The results show that sample thickness and penetrator size play significant roles in the nature or extent of damage. The results also show that strain rate depends on both the striker impact energy, penetrator size, and the target thickness. Cracks were found to propagate faster in thin specimens in all the damage thresholds.
An innovative design of closed-loop cooling system for a stator airfoil consists of a number of internal cooling passages wrapping around both pressure and suction sides of the airfoil. The cooling passages feature (1) jet impingement post a sharp 90-degree turn at the passage inlet, (2) turbulators on the outermost wall, and (3) a nearly 180-degree turn in the trailing edge. In addition, the passage has an irregular cross-section and varies throughout its entire length. A series of heat transfer tests have been performed at Re = 17,000 ∼ 61,000, compared to this tests which uses a new approach, so-called the hybrid liquid crystal technique. The magnitude of local heat transfer coefficient rises sharply in three regions. The first maximum occurs in the region subjected to direct jet impingement as the flow turns into the channel. Compounded with the inlet effect, this maximum, in fact, is the highest heat transfer coefficient over the entire passage. The second and third peaks, both are comparable in magnitude, locate near the trailing edge of the airfoil where the flow experiences a 180-degree turn and near the passage exit with a 90-degree turn. The average value of heat transfer coefficient over the entire passage is about 1.9∼ 2.5 times higher than that with fully developed turbulent flow in a straight channel. This level of enhancement is comparable to that of the conventional ribturbulators with a 90-degree angle-of-attack.
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