Damage tolerance

It is critical that surface treatment conditions be optimized to composite properties since overtreatment as well as undertreatment will degrade composite properties. Typically composite interlaminar shear strength (ILSS), in-plane shear, and transverse tension ate used to assess the effectiveness of surface treatment. More recently damage tolerance properties such as edge delamination strength, open hole compression, and compression after impact have become more important in evaluating the toughness of composite parts. 

Ceramic matrices are usually chosen on their merits as high temperature materials reinforcements are added to improve their toughness, reUabiUty, and damage tolerance. The matrix imparts protection to the reinforcements from chemical reaction with the high temperature environment. The principal concerns in choosing a matrix material are its high temperature properties, such as strength, oxidation resistance, and microstmctural stabiUty, and chemical compatibihty with the reinforcement. 

Ceramic matrix composites are candidate materials for high temperature stmctural appHcations. Ceramic matrices with properties of high strength, hardness, and thermal and chemical stabiUty coupled with low density are reinforced with ceramic second phases that impart the high toughness and damage tolerance which is required of such stmctural materials. The varieties of reinforcements include particles, platelets, whiskers and continuous fibers. Placement of reinforcements within the matrix determines the isotropy of the composite properties. 

W. Elber, The Significance of Fatigue Crack Closure , Damage Tolerance in Aircraft Structures, ASTM STP 486, 1971, pp. 230 242. 

The main disadvantage of ceramic materials is their brittleness, which leads to catastrophic failure even at high temperatures. Ceramics are not damage tolerant, especially when loaded under tensile or bending stress. 

Fiber reinforced ceramics such as C/SiC, SiC/SiC can be manufactured by the polymer infiltration and pyrolysis technique at reasonable cost. The developed production technique allows the manufacturing of large and complex structures comparable to fiber-reinforced plastics. The material has excellent high temperature resistance, low density, and good damage tolerance, and is therefore well... 

Fig. 7. Fiber delamination, fiber pull-out and matrix cracks lead to a high energy dissipation and to good damage tolerance (SiC/SiC)ii...

Structural performance requirements for blast resistant design include limits imposed on member deflections, story drifts and damage tolerance levels. Conventional serviceability requirements are not applicable for the one time severe blast loading conditions. See Chapter 5 for additional information. 

UBC13 153 Rad5 [73] Heterodimerizes with Mms2 (UEV) [72] DNA-damage tolerance [72] via polyubiquiti-nation of PCNA [65] (non-proteolytic function)... 

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