Sliding joints in 3D beams: conserving algorithms using the master-slave approach

This paper proposes two time-integration algorithms for motion of geometrically exact 3D beams under sliding contact conditions. The algorithms are derived using the socalled master–slave approach, in which constraint equations and the related time-integration of a system of differential and algebraic equations are eliminated by design. Specifically, we study conservation of energy and momenta when the sliding conditions on beams are imposed and discuss their algorithmic viability. Situations where the contact jumps to adjacent finite elements are analysed in detail and the results are tested on two representative numerical examples. It is concluded that an algorithmic preservation of kinematic constraint conditions is of utmost importance.Peer ReviewedPostprint (author's final draft

Cheating: It depends how you define it

Cheating in academia is defined multidimensionally and might include dishonesty, fraud, stealing, and unauthorized use. This behaviour appears to be on the rise in higher education, though it may be somewhat subjective. Beyond the ethical issue of cheating, inadequately learned skills and unqualified practitioners put lives at risk (e.g., medicine, engineering), as well as the institution’s reputation and integrity in producing proficient graduates. We asked Canadian students and faculty from a two-year college to define academic cheating in their own words and rate a number of behaviours to indicate their perception of whether the behaviour should be considered cheating or not. Overall, there was a great overlap between the themes evoked in students’ and faculty’s definitions of cheating. Differences between students’ and faculty’s ages might suggest a different degree of moral reasoning which may have impacted the responses. This study further contributes to knowledge about cheating because we surveyed college students (rather than university students), which are greatly under-represented in the literature

Identity Status: The Impact on Academic Performance

The purpose of this mixed methods study was to understand how environmental factors contributed to identity achievement with potentially positive effects on academic performance for fifth grade students. Early adolescents have not been studied partly because of the predominant acceptance of Erikson\u27s (1968) theory of identity development. Four questions guiding the study were (a) whether adolescents acquired an Achieved identity status earlier than previous research has suggested, (b) if environmental issues such as familial obligations expedited identity achievement, (c) if identity status impacted academic performance, and (d) what was the impact of an Achieved identity on academic performance. Participants were 78 fifth-grade students (39 girls and 39 boys) ages 10-13 from two schools in the southwestern United States. Their ethnicities included Latino (51%), Black (18%), White (10%), Other (9%), Biracial/Multiracial (8%), and Asian/ South Pacific Islander (4%). The organizing theory for the study was Marcia\u27s (1966) development of identity statuses and its constructs of exploration and commitment as determinants of identity status (Diffused, Foreclosed, Moratorium, and Achieved). Participants completed two quantitative measures of ego identity--the Ego Identity Process Questionnaire (EIPQ) by Balistreri, Busch-Rossnagel, & Geisinger (1995) and the Extended Objective Measure of Ego Identity Status (EOM-EIS-II) by Adams, Bennion, & Huh (1989) and one semi- structured interview. The results identified a majority of the participants as Diffused status (n = 11, 55%), or Foreclosed status (n = 6, 30%). Only three were Moratorium status (n = 3, 15%), and none were Achieved status. Children who appeared mature and responsible, for example taking care of younger siblings, were burdened with issues of daily survival that took precedence over school. Conversely, children without responsibilities could focus on school and think about their future

Sliding joints in 3D beams: conserving algorithms using the master-slave approach

This paper proposes two time-integration algorithms for motion of geometrically exact 3D beams under sliding contact conditions. The algorithms are derived using the so-called master–slave approach, in which constraint equations and the related time-integration of a system of differential and algebraic equations are eliminated by design. Specifically, we study conservation of energy and momenta when the sliding conditions on beams are imposed and discuss their algorithmic viability. Situations where the contact jumps to adjacent finite elements are analysed in detail and the results are tested on two representative numerical examples. It is concluded that an algorithmic preservation of kinematic constraint conditions is of utmost importance

Master-slave approach for the modelling of joints with dependent degrees of freedom in flexible mechanisms

The analysis of multibody systems requires an exact description of the kinematics of the joints involved. In the present work the master–slave approach is employed and endowed with the possibility of including several more complex types of joints. We present the formulation for joints where some relation between the different released degrees of freedom exists such as the screw joint, the rack‐and‐pinion joint or the cam joint. These joints are implemented in conjunction with geometrically exact beams and an energy‐momentum conserving time‐stepping algorithm

On Gc, Jc and the characterisation of the mode-I fracture resistance in delamination or adhesive debonding

We focus on the mode-I quasi-static crack propagation in adhesive joints or composite laminates, where inelastic behaviour is due to damage on a relatively thin interface that can be effectively modelled with a cohesive-zone model (CZM). We studied the difference between the critical energy release rate, G c , in- troduced in linear elastic fracture mechanics (LEFM), and the work of separation, , i.e. the area under the traction-separation law of the CZM. This difference is given by the derivative, with respect to the crack length, of the energy dissipated ahead of the crack tip per unit of specimen width. For a steady- state crack propagation, in which that energy remains constant as the crack tip advances, this derivative vanishes and =G c . Thus, the difference between and G c depends on how far from steady-state the process is, and not on the size of the damage zone, unlike what is stated elsewhere in the literature. Therefore, even for very ductile interfaces, G c = for a double cantilever beam (DCB) loaded with mo- ments and their difference is extremely small for a DCB loaded with forces. We also show that the proof that the critical value of the J integral, J c , is equal to the nonlinear energy release rate is not valid for a non-homogeneous material. To compute G c for a DCB, we use a method based on the introduction of an equivalent crack length, a eq , where the solution is a product of a closed-form part, which does not require the measurement of the actual crack length, and of a corrective factor where the knowledge of the actual crack length is required. However, we also show that this factor is close to unity and therefore has a very small effect on G c