Effect of carbon nanotube lengths on the mechanical properties of epoxy resin: an experimental study

Batches of multi-walled carbon nanotubes having an average length of 2091 nm were aggressively tip-ultrasonicated to produce shortened carbon nanotubes having average lengths of 1689 nm, 1332 nm, 992 nm and 503 nm. Raman spectroscopic analysis confirmed that the shortened carbon nanotubes retained their crystallinity after the shortening process. Carbon nanotubes were then dispersed in the epoxy matrix using high-shear mixing technique (calendering). The mechanical properties were measured for the cured epoxy–0.1 wt% carbon nanotube nanocomposites having carbon nanotubes of different lengths. It was found that the nanocomposites containing long carbon nanotubes (2091 nm and 1689 nm) possess higher tensile strength, elastic modulus, fracture strain and fracture toughness as compared to nanocomposites containing short carbon nanotubes (1332 nm, 992 nm and 503 nm)

Learning Participation as Systems Practice

Learning participation only makes sense if it is purposeful. From our perspective its primary purpose is to achieve more effective managing in situations of complexity and change. We describe our evolving understandings and practices (a praxeology) for Systems Practice for managing complexity, built on 30 years of developing supported open learning opportunities in the area of Systems within the curriculum of The Open University (UK). We ground this description in two specific examples of how notions of participation are incorporated conceptually and practically into a learner's programme of study by considering: i) the postgraduate course 'Environmental Decision Making. A Systems Approach' (T860) and ii) the undergraduate course 'Managing Complexity. A Systems Approach' (T306). From these courses, as well as a historical review of teaching practice, we identify nine pedagogic design features of our practice. Metaphorically all of the elements of our praxeology can be understood through the lens of the practitioner as chorographer (a systematic describer and analyst of regions) and choreographer (one versed in creating a dance of the emotions)

A correlation between failure angle and constituent for Al-AlN composites under uniaxial tensile conditions

Al-AlN composites with different AlN reinforcement fractions and porosity were fabricated through nitridation of laser-sintered AA 6061 powder followed by infiltration with AA 6061. Their failure behaviors were investigated under uniaxial tensile loading conditions. Tensile testing and fractography indicate that the fracture mode changes gradually from ductile to brittle fracture with increasing AlN reinforcement or porosity. An analysis of the fractured Al-AlN tensile samples reveals that the failure surface angle, h, is dictated by the volume fraction of the matrix, fm, in a form of tan h = fm 5.5