broken bags are then studied in detail to determine the nature and location of the failures, and the results of the analyses are used to develop proposals for improving the performance of the bags.

Constraints

We defined “constraints” as the physical, economical, legal, political, social, ethical, aesthetic, and time limitations inherent to or imposed upon the design of a solution to a technical problem. Our analysis suggests that constraints are a frayed fragment of thread running through some of the beads. The frayed nature of the thread indicates the ambiguities of the concept of constraints and the many ways it is interpreted.

In engineering practice, constraints frame the problem to be addressed by defining the salient conditions under which it must be solved. These conditions can include budget limitations, government regulations, patent laws, and project deadlines, among others. In the curricular initiatives that address this concept at all, constraints were presented as “things”—usually time, money, and materials—that limit the design process. However, “City Technology” includes rules and regulations among constraints on the design process. Gateway to Technology includes aesthetic considerations and the limits of human capabilities in its definition. A module on Reverse Engineering in the “Designing for Tomorrow” curriculum introduces the idea of constraints as limitations in materials properties and manufacturing processes.

Other factors in addition to constraints that can help define a problem include design specifications (i.e., features of the final solution, without which the design will not solve the problem) and design criteria (i.e., the parameters that must be tested to evaluate the suitability of final product). In the curricula, the terms constraints, specifications, and criteria are usually used interchangeably.

The confusion is most apparent in the learning activities. For example, in a design unit, Power and Energy: The Whispers of the Willing Wind from the “Invention, Innovation, and Inquiry” curriculum, constraints for the design and construction of a working model of a windmill are outlined. The “constraints” stipulate that the tower must be no more than 12 inches high, that the side of the base must not exceed 6 inches, and that the turbine must be less than 5 inches in diameter. The reasons for these specifications are not disclosed, but they do not appear to have a relationship to the problem being addressed or to reflect engineering design practices. Their purpose seems to



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