Future Work Will Determine

Tfrs Composite Practicability.

Studios show that tungsten-fiber-reinforced superalloy composites potentially are promising materials for advanced high-temperature components, and that complex-shaped composite parts can be made successfully. However, further research Is needed to ge­nerate a database for design, as well as to develop and verify structural analysis and failure models to optimize design and maximize performance advantages.

Most refractory metal wire alloys hove been developed by the electric-lamp industry for strength at incandescent temperatures, and it is fortunate that they also have outstanding properties in the 1095⁰C temperature range. Efforts are underway to develop new refractory metal wires, specifically designed for maximum long-time creep strength in the 900⁰ to 1325°C temperature range. The improved properties of new fibers, combined with improvements in structural analysis and design, will aid in the development of TFRS composites for advanced airbreathing and rocket engine applications, as well as other high-temperature materials applications.

Notes: 1. directionally solidified single crystals and eutectic - материалы с многокристаллической или эвтектической структурой, полученные направленной кристаллизацией

2. Angle-plied fiber orientation - угловая ориентация упрочняющих волокон

3. heavily worked fibers - сильноупрочненные волокна

Задание 7. Make up an oral (or written) report on "Composi­tion and Advantages of TFRS composites"⁷.

The following words and word combinations might be useful for it: Contain; reinforcement; stronger than; although; density; ruptu­re strength/density ratio; the first choice for high-temperature FRS composite reinforcement; the key factor in matrix selection; compatibility with reinforcement; since; interface reactions; oc­cur; between fibers and matrices; the least reactive; Fe Cr Al T alloy; provide; not only...but also; improved ductility and oxi­dation resistance.

Temperature advantage of 170⁰C; over conventional alloys; over the strongest superalloy; ductile superalloy matrix; reduce; ther­mal strains; by plastic deformation; thermal conductivity.

Design Fundamentals for Composites

from Mechanical Engineering, September 1987

The properties of a composite depend on many factors: com­ponent properties, relative proportions, size and shape, state of aggregation and agglomeration, relative dispersion and orien­tation, and level of interphase adhesion. Composite properties are also subject to change due to environmental effects, aging, thermal conditions, and other factors. With so many variables, estimating composite properties analytically can be a very comp­lex, and unrewarding, task. However, simple equations for preli­minary designs are available which make working with composites as easy as with conventional materials.

A first approximation of many mechanical properties based on the Rule of Mixtures (in which overall properties are a sum of the component properties) can be made for unidirectional, conti­nuous fiber composites. Tensile modulus, for example, may be es­timated from

E_c=V_fE_f+V_mE_m

Where E_c is the modulus, E_f and E_m are modules of the reinforcement and matrix, respectively, and V_f and V_m are the volume fracti­ons of reinforcement and matrix, respectively. Fairly precise an­alogous equations have been developed for longitudinal Poisson's ratio, tensile strength, and other properties.

Similar equations exist for transverse properties. Trans­verse modulus, for example, may be estimated from

E_c=

Either equation (tensile or transverse) may be generalized for any number of components.

A more accurate estimate, «blob la adequate for many practi­cal design predictions of transverse composite modulus, have been developed. Called the Halplng-Tsai equation (after its developers) it can be used to approximate the properties of a composite as a somewhat complex function of reinforcement geometry, packing, and loading conditions. For fibers with circular or square cross-section, the simplified Tsai-Halpin equation for transverse modulus is

E_c= , where ή=

The properties of many other reinforcement systems may be calcu­lated with the Т-H equation, though some coefficients must be modified.

These and many other equations have been developed or derive ed to reflect the rapid fall-off of the properties when loads are not applied in the direction of tee reinforcement, the effect of critical fiber length, and other more asotiric considerations. Composite properties may be estimated to a fair degree of accu­racy free these and other relatively simple equations. If greater accuracy is required, there are more complex equations available.