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The pursuit for cheap, low-density and high-performance materials in the design of aircraft engine blades raises wide-ranging challenges to the materials and structural design engineers. Traditionally, these components have been fabricated using expensive materials such as lightweight titanium alloys and polymer composite materials composites. The present study investigates the use of a sandwich foam fan blade made of solid face sheets and a metal foam core. The face sheets and the metal foam core material were an aerospace grade precipitation-hardened 17-4 stainless steel with high strength and high toughness. The stiffness of the sandwich structure is increased by separating the two face sheets by a foam core. The resulting structure possesses a high stiffness while being lighter than a similar solid construction. Since the face sheets carry the applied bending loads, the sandwich architecture is a viable engineering concept. The material properties of 17-4 precipitation-hardened metal foam are briefly reviewed to describe the characteristics of the sandwich structure for a fan blade application. Vibration characteristics and design criteria on the 17-4 precipitation-hardened metal foam core sandwich blade design with different combinations of skin thickness and core volume are presented with a comparison to a solid titanium blade. [ABSTRACT FROM AUTHOR]

Calibrations relating back-face strain (BFS) to crack length in precracked flexure specimens were developed for different strain gage sizes. The functions were verified via experimental compliance measurements of notched and precracked ceramic beams. Good agreement between the functions and experiments occurred, and fracture toughness was calculated using several operational methods: maximum test load and optically measured precrack length; load at 2% crack extension and optical precrack length; and maximum load and BFS crack length. All the methods gave comparable results. The initiation toughness, KIi, was also estimated from the initial compliance and load. The results demonstrate that the stability of precracked ceramic specimens tested in four-point flexure is a common occurrence, and that methods such as remotely monitored load-point displacement are only adequate for detecting stable extension of relatively deep cracks. [ABSTRACT FROM AUTHOR]

The space shuttle foams are rigid closed-cell polyurethane foams. The two foams used most extensively on the space shuttle external tank are BX-265 and NCFI24-124. Because of the foaming and rising process, the foam microstructures are elongated in the rise direction. As a result, these two foams exhibit a nonisotropic mechanical behavior. A detailed microstructural characterization of the two foams is presented. Key features of the foam cells are described and the average cell dimensions in the two foams are summarized. Experimental studies are also conducted to measure the room temperature mechanical response of the two foams in the two principal material directions (parallel to the rise and perpendicular to the rise). The measured elastic modulus, proportional limit stress, ultimate tensile strength, and Poisson's ratios are reported. The generalized elongated Kelvin foam model previously developed by the authors is reviewed and the equations which result from this model are summarized. Using the measured microstructural dimensions and the measured stiffness ratio, the foam tensile strength ratio and Poisson's ratios are predicted for both foams and are compared with the experimental data. The predicted tensile strength ratio is in close agreement with the measured strength ratio for both BX-265 and NCFI24-124. The comparison between the predicted Poisson's ratios and the measured values is not as favorable. [ABSTRACT FROM AUTHOR]

Abstract: A micro-mechanics model for non-isotropic, open-celled foams is developed using an elongated tetrakaidecahedron (Kelvin model) as the repeating unit cell. Assuming the cell edges possess axial and bending rigidity, the mechanics of deformation of the elongated tetrakaidecahedron lead to a set of equations for the Young’s modulus, Poisson’s ratio and tensile strength of the foam in the principal material directions. These equations are written as a function of the cell edge lengths and cross-section properties, the inclination angle and the strength and stiffness of the solid material. This micro-mechanics model employs an elongated Kelvin model geometry which is more general than that employed by previous authors, as the size and shape of the repeating unit cell are defined by specifying three independent dimensions. As a result, the model accounts for an additional variation in the unit cell shape which is not accounted for in the previous models. The effect of this additional shape parameter on the non-isotropic stiffness and strength behavior is demonstrated and the advantages of this more general micro-mechanics model are illustrated. [Copyright &y& Elsevier]

Reliable engine-weight estimation at the conceptual design stage is critical to the development of new aircraft engines. It helps to identify the best engine concept amongst several candidates. In this paper, the major enhancements to NASA's engine-weight estimate computer code (WATE) are described. These enhancements include the incorporation of improved weight-calculation routines for the compressor and turbine disks using the finite difference technique. Furthermore, the stress distribution for various disk geometries was also incorporated, for a life-prediction module to calculate disk life. A material database, consisting of the material data of most of the commonly used aerospace materials, has also been incorporated into WATE. Collectively, these enhancements provide a more realistic and systematic way to calculate the engine weight. They also provide additional insight into the design tradeoff between engine life and engine weight. To demonstrate the new capabilities, the enhanced WATE code is used to perform an engine weight/life tradeoff assessment on a production aircraft engine. [ABSTRACT FROM AUTHOR]

The development of advanced high-performance constant-volume–combustion-cycle engines (CVCCE) requires robust design of the engine components that are capable of enduring harsh combustion environments under high-frequency thermal and mechanical fatigue conditions. In this study, a simulated engine test rig has been established to evaluate thermal fatigue behavior of a candidate engine combustor material, Haynes 188, under superimposed CO2 laser surface impulsive thermal loads (30–100 Hz) in conjunction with the mechanical fatigue loads (10 Hz). The mechanical high-cycle fatigue (HCF) testing of some laser preexposed specimens has also been conducted at 100 Hz to determine the laser surface damage effect. The test results have indicated that material surface oxidation- and creep-enhanced fatigue is an important mechanism for the surface crack initiation and propagation under the simulated CVCCE engine conditions. [Copyright &y& Elsevier]