Computer-Aided Materials Selection During Structural Design (1995) / Chapter Skim
Currently Skimming:
4 Information Technologies Pertinent to the Materials Selection Process
4 Information Technologies Pertinent to the Materials Selection Process
Pages 25-36
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From page 25... ...
This section provides a brief overview of the levels of knowledge representation in the automation of technical memory and discusses the principal methods for representing materials knowledge within a CAMSS to facilitate the design process. Appendix A contains a brief overview of some of the knowledge representation techniques discussed in this chapter.
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From page 26... ...
Many companies have custom-built basic systems for their own applications. Table 4-1 summarizes representative computer-aided system application areas that relate to the materials information used in the design process in a manner consistent with the vision discussed In Chapter 3.
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From page 27... ...
-l t} ~ i: .c I: ~ 0 ~ .e 3 ·~ ·3 es 8 ~ os ID c: 0 _ ~ _ o o ~ 0 o.
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From page 28... ...
, have anode a start, but industrial data limitations have resulted in their falling short of the needs for knowledge-base approaches to design. The situation is currently little better than it was in 1983 when a National Materials Advisory Board report stated: There is no national policy in the United States directed toward a rational system of materials properties data management and the situation in this area is best described as chaotic" (NRC, 1983~.
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From page 29... ...
The level of graphic rendering has reached an impress~ve level, but all design decisions are essentially made by the design engineer with little or no decision support, or reasoning, other than visual feedback. Reasoning falls into the two major categories of synthesis (i.e., the systematic creation of alternatives as the product design and the design process become increasingly more specific)
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From page 30... ...
Reasoning about materials needs to be closely coordinated with decisions regarding shape and geometry. Considering the earlier example of the car space frame, a novel design was created by combining material properties and processing knowledge with spatial layout.
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From page 31... ...
Process modeling discussed in the context of this report deals with unit processes such as casting, forging, rolling, hot isostatic processing, heat treating, machining, chemical vapor deposition, and composite material fabrication. Constitutive modeling may be one of several elements in the overall process model.
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From page 32... ...
The important properties include emissivity, heat capacity, heat of fusion, melting temperature, density, surface tension, thermal diffusivity, and materials viscosity as a function of temperature and shear strain rate. Comprehensive thermophysical properties, constitutive models for nonlinear behavior, intrinsic processing maps, and databases of microstructure-property relationships are needed for industrial process modeling as influenced by prior thermomechanical history.
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From page 33... ...
Finally, and most importantly in the present context, these models can be incorporated into a concurrent engineering design process. One of the most significant advances in nondestructive evaluation over the last decade has been the evolution of quantitative nondestmctive evaluation (QNDE)
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From page 34... ...
For example, in the case of ultrasound as interrogating energy, this description requires computations of the transducer radiation pattern, refraction of the beam at the part's surface, the beam profile, and the propagation characteristics in the host material including effects of material anisotropy, attenuation, and diffraction losses. Detailed modeling of the field-flaw interactions that generate the measurement system's response function are also included, as well as information on material properties and other conditions that increase variability and add uncertainty to the measurement results.
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From page 35... ...
A POD curse shows the probability of a flaw's detection as a function of flaw size for a specific inspection technique. For an ideal technique, the POD of flaws smaller than a size predetermined by performance requirements and material properties is zero, while the POD for any flaw greater than this size is unity.
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From page 36... ...
Some engineers, such as manufacturing mechanical engineers, are highly skilled at using computers and doing PEA but do not have sufficient knowledge about the behavior of materials under processing conditions. In contrast, materials scientists and engineers have a better understanding of material behavior but lack sufficient training in the use of computers and com puter-aided systems in manufacturing.
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