Torque Limit of a Mechanical Fastener in a Graphite/Epoxy Joint

Presently there is a lack of confidence amongst engineers when specifying the preload of a mechanical fastener in a composite joint due to a lack of a fundamental knowledge base regarding the behavior of composites under fastener compressive load. As such, a novel experimental procedure was developed herein to determine the through-the-thickness compressive (TTTC) material properties. A total of 206 property tests were performed on four different graphite/epoxy material systems. The results confirmed that TTTC material properties vary with fiber orientation, laminate thickness, fiber volume fraction, and even laminate surface finish. Hence, the \u27rule of mixtures\u27 provides a poor estimate of the TTTC modulus in that it fails to account for any of these variables. Finally, acoustic emission nondestructive testing, along with a modified approach to MSFC-STD-486B, Torque Limits for Standard Threaded Fastener, were used to determine the torque limit of a fastener in a single lap joint. The laminate configuration examined in these tests was manufactured in accordance with the MIL-HDBK-17 design code. The results demonstrated the inability of the fasteners employed to damage the one composite system investigated: fastener thread failure occurred first. Further study is necessary to confirm or refute these results for other composite systems and joint configurations

Tetris is Hard, Even to Approximate

In the popular computer game of Tetris, the player is given a sequence of tetromino pieces and must pack them into a rectangular gameboard initially occupied by a given configuration of filled squares; any completely filled row of the gameboard is cleared and all pieces above it drop by one row. We prove that in the offline version of Tetris, it is NP-complete to maximize the number of cleared rows, maximize the number of tetrises (quadruples of rows simultaneously filled and cleared), minimize the maximum height of an occupied square, or maximize the number of pieces placed before the game ends. We furthermore show the extreme inapproximability of the first and last of these objectives to within a factor of p^(1-epsilon), when given a sequence of p pieces, and the inapproximability of the third objective to within a factor of (2 - epsilon), for any epsilon>0. Our results hold under several variations on the rules of Tetris, including different models of rotation, limitations on player agility, and restricted piece sets.Comment: 56 pages, 11 figure

On a "stability" in the linear complementarity problem

In this work we rewrote the linear complementarity problem in a formulation based on unknown projector operators. In particular, this formulation allows the introduction of a concept of "stability" that, in a certain way, might explain the way block pivotal algorithm performs. (c) 2008 Elsevier Inc. All rights reserved.info:eu-repo/semantics/publishedVersio

The development of a vocational-specific locus of control scale to examine the relationships between locus of control, job satisfaction and voluntary job turnover

The purposes of this study were to develop a locus of control scale specific to vocational needs and to use the scale to examine the relationships between vocational need strength, need satisfaction, locus of control and voluntary worker turnover. Voluntary turnover was defined as intent to leave one's job, the dependent variable. The Kostreva Vocational Attitude Scale (KVAS) was designed to measure intent-to-leave and Internal (I), Powerful Others (P) and Chance (C) locus of control, in Levenson's (1972) format, based on Rotter's (1966) theory and the 20 need factors of the Theory of Work Adjustment (Dawis et al. 1968). Hoyt reliability coefficients were .74 I, .80 P, .87 C and .95 for intent-to-leave. As predicted, KVAS sub-scales had loworder positive correlations to Levenson's I, P and C scales. The Minnesota Importance Questionnaire, assessing vocational need strength, the Minnesota Satisfaction Questionnaire, assessing vocational need satisfaction, and the KVAS, were administered to 101 randomly selected, employed persons, ages 20-40 (52 men, 49 women). Consistent with prior research, the intending-to-leave group had a significantly lower mean score on overall job satisfaction than the not-intending-to-leave group (p=.001). Step-wise regression analyses indicated significant correlations (p < .05) between: 1) low need satisfaction and intent-to-leave on 17 of 20 vocational need factors; 2) high need strength and intent-to-leave on the Advancement factor; and 3) high Chance locus of control and intent-toleave on the Social Status factor. One-way ANOVA showed a significantly higher mean score on overall Chance locus of control for the leaving group (p=.021), but no differences on Internal or Powerful Others. Post hoc discriminant analysis indicated younger age to be significantly related to intent-to-leave. Age and total job satisfaction correctly classified 75% of subjects to leaving and not-leaving groups (i.e., a younger individual who indicated low job satisfaction was likely to be in the leaving group). Gender and years of school were not related to leaving. Further study on actual turnover versus intent-to-leave was suggested, as was additional testing with the KVAS

The Component Packaging Problem: A Vehicle for the Development of Multidisciplinary Design and Analysis Methodologies

This report summarizes academic research which has resulted in an increased appreciation for multidisciplinary efforts among our students, colleagues and administrators. It has also generated a number of research ideas that emerged from the interaction between disciplines. Overall, 17 undergraduate students and 16 graduate students benefited directly from the NASA grant: an additional 11 graduate students were impacted and participated without financial support from NASA. The work resulted in 16 theses (with 7 to be completed in the near future), 67 papers or reports mostly published in 8 journals and/or presented at various conferences (a total of 83 papers, presentations and reports published based on NASA inspired or supported work). In addition, the faculty and students presented related work at many meetings, and continuing work has been proposed to NSF, the Army, Industry and other state and federal institutions to continue efforts in the direction of multidisciplinary and recently multi-objective design and analysis. The specific problem addressed is component packing which was solved as a multi-objective problem using iterative genetic algorithms and decomposition. Further testing and refinement of the methodology developed is presently under investigation. Teaming issues research and classes resulted in the publication of a web site, (http://design.eng.clemson.edu/psych4991) which provides pointers and techniques to interested parties. Specific advantages of using iterative genetic algorithms, hurdles faced and resolved, and institutional difficulties associated with multi-discipline teaming are described in some detail

Estimated central blood volume in cirrhosis

The estimated central blood volume (i.e., blood volume in the heart cavities, lungs and central arterial tree) was determined by multiplying cardiac output by circulatory mean transit time in 19 patients with cirrhosis and compared with sympathetic nervous activity and circulating level of atrial natriuretic factor. Arterial norepinephrine level, an index of overall sympathetic nervous activity (3.08 nmol/L in patients vs. 1.36 nmol/L in controls; p < 0.01) was negatively correlated (r = -0.54, p < 0.01) with estimated central blood volume (mean = 23 ml/kg in patients vs. 27 ml/kg in controls; p < 0.05). Similarly, renal venous norepinephrine level (an index of renal sympathetic tone; 4.26 nmol/L in patients vs. 1.78 nmol/L in controls; p < 0.01) was inversely correlated with estimated central blood volume (r = -0.53, n = 18, p < 0.02). No significant correlation could be established between arterial atrial natriuretic factor level (8.9 pmol/L in patients vs. 9.6 pmol/L in controls; not significant) and estimated central blood volume. Hemodynamic values were subsequently modified with oral propranolol (80 mg). During -adrenergic blockade, the mean estimated central blood volume was not altered significantly, except in six patients who exhibited decreases in mean arterial blood pressure (85 to 69 mm Hg; n = 6) and decreases in mean estimated central blood volume (23.2 to 20.6 ml/kg; n = 6, p < 0.05). Slight increases were observed in mean right atrial pressure (2.2 to 3.7 mm Hg; n = 14, p < 0.05); this change was positively correlated with the change in estimated central blood volume (r = 0.44, n = 14, p = 0.06). In conclusion, reduced estimated central blood volume probably unloads volume receptors and baroreceptors, thus provoking enhanced overall and renal sympathetic nervous activity and thereby contributing to increased water and salt retention in cirrhosis. During -adrenergic blockade estimated central blood volume changes correlated with alterations in preload and afterload. These findings indicate that central circulatory and arterial underfilling is a key element of the hemodynamic derangement observed in cirrhosis

Increasing the simulation performance of large-scale evacuations using parallel computing techniques based on domain decomposition

Evacuation simulation has the potential to be used as part of a decision support system during large-scale incidents to provide advice to incident commanders. To be viable in these applications, it is essential that the simulation can run many times faster than real time. Parallel processing is a method of reducing run times for very large computational simulations by distributing the workload amongst a number of processors. This paper presents the development of a parallel version of the rule based evacuation simulation software buildingEXODUS using domain decomposition. Four Case Studies (CS) were tested using a cluster, consisting of 10 Intel Core 2 Duo (dual core) 3.16 GHz CPUs. CS-1 involved an idealised large geometry, with 20 exits, intended to illustrate the peak computational speed up performance of the parallel implementation, the population consisted of 100,000 agents; the peak computational speedup (PCS) was 14.6 and the peak real-time speedup (PRTS) was 4.0. CS-2 was a long area with a single exit area with a population of 100,000 agents; the PCS was 13.2 and the PRTS was 17.2. CS-3 was a 50 storey high rise building with a population of 8000/16,000 agents; the PCS was 2.48/4.49 and the PRTS was 17.9/12.9. CS-4 is a large realistic urban area with 60,000/120,000 agents; the PCS was 5.3/6.89 and the PRTS was 5.31/3.0. This type of computational performance opens evacuation simulation to a range of new innovative application areas such as real-time incident support, dynamic signage in smart buildings and virtual training environments

Computational complexity of LCPs associated with positive definite symmetric matrices

Murty in a recent paper has shown that the computational effort required to solve a linear complementarity problem (LCP), by either of the two well known complementary pivot methods is not bounded above by a polynomial in the size of the problem. In that paper, by constructing a class of LCPs—one of order n for n ≥ 2—he has shown that to solve the problem of order n , either of the two methods goes through 2 n pivot steps before termination.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47905/1/10107_2005_Article_BF01588254.pd