Detection and Localization of Delaminations in Thin Carbon Fiber Reinforced Composites with the Ultrasonic Polar Scan

In this paper, the hybrid compliance-stiffness matrix method for simulating wave propagation in (delaminated) multilayered media with viscoelastic anisotropy has been confronted with high-quality amplitude and phase experiments on delaminated composites, obtained using the ultrasonic polar scan setup (UPS) in transmission by considering harmonic as well as pulsed ultrasound. Results are presented for multiple thin carbon/epoxy laminates with an artificial edge delamination induced by a foil insert, showing a good agreement between experimental recording and numerical modeling. The obtained results further reveal the feasibility of the harmonic UPS to detect and even locate the depth-position of multiple delaminations in fiber reinforced composites. Considering that the harmonic UPS method does not rely on the detection of different echoes like the classical C-scan, but rather expounds the conditions for efficient stimulation of guided waves in the solid, the method is found to be highly suited for inspecting thin composite materials for the presence of delaminations.     

The role of crazes in the crack growth of polyethylene

Brittle slow crack growth, or stress cracking, is a major concern in many applications of polyethylene materials. Using a constant tensile load test and removing specimens prior to complete failure, details of the crack tip region can be discerned in both butene and hexene copolymerized polyethylene. In both the presence and absence of an accelerating environment (Igepal CO-630), it was found that crazes formed at the crack tip, although secondary crazes were also evident in the specimens removed from the Igepal. Multiple crack arrest lines were clearly evident, suggesting a stick-slip mechanism under static load. The appearance of the craze zone at the crack tip can be explained through invoking an interlamellar failure model.     

Contingency detection and the contingent organization of behavior in interactions: Implications for socioemotional development in infancy.

In this report, the authors review studies addressing the issue of contingencies in social and nonsocial contexts during infancy. The review is divided into 4 groups of studies that suggest that (a) young infants detect contingencies unrelated to their behavior; (b) infants detect contingencies involving their behavior; (c) the study of contingency is pertinent for addressing behavioral organization within parent-infant interaction; and (d) there is a link between behavioral contingency in early infancy and global measures of socioemotional development that are predictive of social functioning at later points during childhood. Throughout the report, the pertinence of infant emotional responses during contingency-related tasks is emphasized. Finally, the authors delineate certain enduring questions regarding contingency experience in infancy and suggest ways of organizing research to address some of them. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Calculation of impact transition temperature of low density polyethylene from shift factor via a free volume approach

A relationship between the impact transition temperatureT _i and the stress concentration factorK _s is derived. The relationship involves the temperature shift factora _T; in turn,a _T depends on the free volume. In earlier work in this problem Zewi and Corneliussen [6] utilized the W-L-F equation. Here a more direct relationship betweena _T and the free volume is applied. Satisfactory values ofK _s corresponding to givenT _i are obtained for a wide temperature range; the range also includes temperatures below the glass transition pointT _g. The opinion that a free volume exists between 0 K andT _g is upheld.