William Keat

Design charts for remanufacturing assessment

Abstract A structured approach, based on having cross-functional teams fill out a series of design charts, has been developed for enforcing design for remanufacture considerations throughout a product life cycle. The lists of design attributes and metrics used to evaluate remanufacturability were compiled through consultation with experienced professionals and searches of relevant literature. Short responses and benchmark comparisons were built into the charts to yield quantitative information in a timely fashion. The results can be used to identify opportunities for remanufacturing enhancement, set goals, and measure progress. A case study is presented that illustrates the use of the charts and demonstrates their sensitivity to product modification. Finally, potential barriers to implementation of the charts, as well as facilitators promoting their introduction, are briefly discussed.

Three-dimensional mixed-mode fatigue crack growth in a functionally graded titanium alloy

Abstract The implementation of unitized structure in the aerospace industry has resulted in complex geometries and load paths. Hence, structural failure due to three-dimensional mixed-mode fatigue crack growth is a mounting concern. In addition, the development of functionally graded materials has further complicated structural integrity issues by intentionally introducing material variability to create desirable mechanical behavior. Ti–6Al–4V β-STOA (solution treated over-aged) titanium is a functionally graded metallic alloy that has been tailored for superior fatigue crack growth and fracture response compared with traditional titanium alloys. Specifically, the near-surface material of Ti β-STOA is resistant to fatigue crack incubation and the interior is more resistant to fatigue crack growth and fracture. Therefore, Ti β-STOA is well suited for applications where surface cracking is a known failure mode. Advances in experimental testing have shown that complex loading conditions and multi-faceted materials can be tested reliably. In this paper, the authors will experimentally generate three-dimensional mixed-mode surface crack data in functionally graded Ti–6Al–4V β-STOA and comment on the effect of the material tailoring.

Limits of crack growth stability in the double cleavage drilled compression specimen

A theoretical investigation of the double cleavage drilled compression specimen was undertaken to define the limits of stable crack growth for a range of geometries and fracture toughnesses typically used in fracture testing of brittle materials. Two-dimensional large displacement solutions for the mode I stress intensity factor were derived using energy methods. Comparisons with finite element results indicate that these models maintain a high level of accuracy well past the onset of unstable crack growth. Crack growth stability was assessed by differentiating the semi-analytical solutions and assembling the results in the form of design curves.

Inverse method of identification for three-dimensional subsurface cracks in a half-space

A procedure is presented which is well suited for three-dimensional subsurface crack identification in a half-space through the inversion of measured surface displacements. The investigation began with the linear, forward problem of generating contour maps of surface deformation produced by a fracture of known geometry and loading which is embedded in a finite medium. The fundamental solutions for tensile and shear multipoles in a half-space provided an efficient mathematical representation of the three-dimensional fracture. The inverse problem of crack identification centers on the development of a hybrid of the Marquardt–Levenberg algorithm. Initial guesses for the constrained set of search variables were determined heuristically from the correspondences between crack geometry and loading and the resulting uplift at the free surface. Physical measurements of surface deformation were taken for a cube of transparent acrylic polyester in which a fracture was hydraulically pressurized. Displacements induced at the surface of the specimen, which were measured by laser interferometry, had a strong correlation with predictions of the computational model (coupled with a finite element discretization). Numerical tests demonstrate the robustness of the inverse methodology even in the presence of the random and systematic errors corresponding to the experimental interferometric measurements.

Development of a mechanically coupled, six degree-of-freedom load platform for biomechanics and sports medicine

Six degree-of-freedom force sensors measure the three forces and three moments applied to a body. In general, there are two main design methodologies for six degree-of-freedom force sensors: mechanically decoupled and mechanically coupled designs. Mechanically decoupled force sensors have the advantage of low cross-sensitivity between the different axes. Unfortunately, decoupled designs necessitate a complicated geometry that leads to difficulties in manufacturing. In a mechanically coupled force sensor, the output signals cannot be attributed directly to specific force/moment components. Instead, the applied loads are derived by multiplying the output signals by a decoupling matrix. This additional computational effort is offset by the simplicity of the design. This work describes the development of a mechanically coupled, six degree-of-freedom load sensor that combines high accuracy and ease of manufacture. The sensor geometry was optimized and the decoupling matrix determined through finite element analysis. A prototype sensor was manufactured and tested. The experimental results validated the analysis and demonstrated the potential advantages of such a sensor.

NONDESTRUCTIVE IDENTIFICATION OF THREE-DIMENSIONAL EMBEDDED CRACKS IN FINITE BODIES BY INVERSION OF SURFACE DISPLACEMENTS

Abstract A combined experimental and numerical investigation demonstrates the effectiveness of a nondestructive method for crack identification based on inversion of surface displacements. Holographic interferometry was used to measure displacements of transparent acrylic cubes containing pressurized cracks. Results compared favorably with those of a three-dimensional hybrid numerical model. A nonlinear inversion code, using Levenberg–Marquardt iterations, was developed in order to search for the fracture geometries which minimized the difference between the theoretical and experimental predictions of surface displacement. The resulting algorithm was able to distinguish clearly the specimen geometries. The requisite level of robustness was achieved by gradually relaxing the constraints on the fracture geometry.

Closing Remarks on the Important Role of Design Projects

Why do a design project? Typical faculty answers are these: they are motivational tools, they apply the analytical methods taught in courses, they help to develop written and oral communication skills, and they teach teaming. In addition, they teach how to see the “big picture” and see that engineering design is, at its core, an unbiased and structured methodology for dissecting and solving complex problems.

Design Step 4. Detailed Design

Try to analyze your design and use simple experiments to model what you cannot totally analyze. Eliminate risk and uncertainties. Make decent diagrams including dimensions for your device.

Design Step 6. Manufacturing and Testing

Think through your manufacturing and testing strategies. Talk to a machinist for an expert opinion of your design. Start immediately, and assign subtasks to all the team members. Enforce deadlines for all the team! Keep the device drawings up to date. Use the provided materials to make the device. Use appropriate material joining methods, be they glue, nails, screws, and so forth. (For the beginners, look at the pictures of all the available tools needed for construction.)

Chapter 10 – Manufacturing Engineering

Solve: Since this story is likely of medieval origin when wild animals and other predictors stalked villages, both straw and sticks were inexpensive and easily obtained. Straw and stick mud houses were common, but sun-dried mud brick houses were more labor intensive and expensive. Straw is weaker than sticks, and both are weaker than bricks. A strong wind (or wolf) could easily damage straw and stick houses, but was less likely to damage brick dwellings. Since all three building materials were available from the local environment, the use of straw and sticks would eventually deplete their supply, but the use of sun-dried mud bricks would have little impact on the pig’s environment.