We investigated the activation of sensory and motor areas involved in the production of typing movements using functional magnetic resonance imaging (fMRI). Eleven experienced typists performed tasks, in which the spatial and temporal requirements as well as the number of digits involved were varied. These included a simple uni-digit repetitive task, a uni-digit sequential task, a dual-digit sequential task, a multi-digit sequential task, and typing text from memory. We found that the production of simple repetitive keypresses with the index finger primarily involved the activation of contralateral primary motor cortex (M1), although a small activation of the supplementary motor area (SMA) and other regions was sometimes observed as well. The sequencing of keypresses involved bilateral M1 and a stronger activation of the SMA and to a lesser extent the premotor area, cingulate gyrus, caudate, and lentiform nuclei. However, the activation of these areas did not exclusively depend on the complexity of the movements, since they were often activated during more simple movements, such as alternating two keypresses repeatedly. Somatosensory and parietal regions were also found to be activated during typing sequences. The activation of parietal areas did not exclusively depend on the spatial requirements of the task, since similar activation was observed during movements within intra-personal space (finger-thumb opposition) and may instead be related to the temporal requirements of the task. Our findings suggest that the assembly of well-learned, goal-directed finger movement sequences involves the SMA and other secondary motor areas as well as somatosensory and parietal areas.

An experimental and analytical investigation was undertaken to improve understanding of the form of long fiber reinforced thermoplastic sheets. The materials tested contained 30 percent by weight of glass fibers in a polypropylene matrix, with the fibers approximately randomly oriented in the plane of sheet. The forming tests covered a range of forming temperatures between the glass transition temperature and the melting point of the polypropylene matrix. The testing geometry was that of a Swift flat-bottomed cup test, which primarily tests bending and drawing behavior of the sheet. An analysis of the process was developed in terms of a continuum model of material behavior with normal anisotropy and rotational symmetry. Results of the forming tests are compared with analytical predictions. Limitations of both the form of the material and the modeling approach are discussed.

Thermoplastic composite materials hold considerable promise for increased use in low cost high volume applications because of the potential for processing by solid phase forming. Unfortunately, because of the wide variety of such materials, inherent variability in properties, and complex temperature and strain rate dependence, large strain behavior of these materials has not been well characterized. Of particular importance is failure during processing due to localized necking instability, and it is this phenomenon that is the primary focus of this study. Large strain behavior under uniaxial tension is characterized over a range of temperatures and strain rates, and a simple linear viscoelastic model is fit to the observed data. The strain rate and temperature dependence is then used to predict limiting tensile strains, based on Marciniak imperfection theory. Excellent correlation was obtained between theory and experiment, and the results are summarized in maps of forming limit as a function of temperature and strain rate. These results suggest that excellent solid phase formability may be obtained for the materials tested under properly chosen conditions.

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