The xylem of Metasequoia glyptostroboides Hu et Cheng is characterized by very low density (average specific gravity = 0.27) and tracheids with relatively large dimensions (length and diameter). The microfibril angle in the S2 layer of tracheid walls is large, even in outer rings, suggesting a cambial response to compressive rather than tensile stresses. In some cases, this compressive stress is converted to irreversible strain (plastic deformation), as evidenced by cell wall corrugations. The heartwood is moderately decay resistant, helping to prevent Brazier buckling. These xylem properties are referenced to the measured bending properties of modulus of rupture and modulus of elasticity, and compared with other low-to-moderate density conifers. The design strategy for Metasequoia is to produce a mechanically weak but hydraulically efficient xylem that permits rapid height growth and crown development to capture and dominate a wet site environment. The adaptability of these features to a high-latitude Eocene palaeoenvironment is discussed.

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Detection of early fatigue damage in composite materials by nondestructive inspection (NDI) techniques has been demonstrated for ±45° Glass/Epoxy, and ±45°/0° Graphite/Glass/Epoxy. Dynamic axial modulus and temperature were monitored continuously with a correlation between temperature rise and modulus decrease observed. The modulus decrease and temperature rise are indicative of irreversible damage in these materials.Torsional modulus measurements and coin tap tests were performed at 0, 10 6 , 5 × 10 6 , and 10 7 cycles, on all fatigue specimens. Other NDI procedures including holographic interferometry, ultrasonics, penetrant, and X-Ray radiography were performed on two specimens of each material to evaluate their effectiveness in detecting fatigue damage. Ultrasonics and holography proved to be effective; however, at this time, no clear quantitative correlation beween structural properties and NDI measurements has been determined.

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This report summarizes a series of U.S. Army sponsored Manufacturing Methods and Tecbnolog , MM&T programs which were ult imately aimed at evaluating and implementing into production the use of the Continuous Seam Diffusion Bonding , CSDB , process to fabricate reliable, lover cost titanium alloy 6A1-~V helicopter main rotor blade spars. The current production process for manufacturing the uIi-6oA Army BLACK HAWK helicopter main rotor blade spars uses a plasma arc weld to join a cold brake formed cylindrical shape titanium sheet pre.-form.