Evaluation of residual strength of polymeric yarns subjected to previous impact loads

The discovery of oil fields in deep and ultra-deep waters provided an opportunity to evaluate the use of  synthetic ropes, complementarily or alternatively to traditional steel-based mooring lines in offshore units, mainly because of the former’s lower specific weight. Considering the series of complex dynamic-mechanical mainly axial loads to which these structures may be subjected, originated from different sources, such as wind, water current, tide, etc., there may be cases when at least one of these lines may possibly face an abrupt, shock-like axial load of considerably larger magnitude. The goal of the present study is to evaluate the residual tensile strength of three different synthetic yarns  (polyester, and two grades of high modulus polyethylene) after exposure to such axial impact loads. It was observed that, for the tested materials, polyester is the one with the largest impact resistance to the conditions evaluated herein, mainly because of its comparatively greater energy absorption properties

Analysis of gap formation at tooth-composite resin interface: effect of C-factor and light-curing protocol

OBJECTIVE: The aim of this study was to evaluate the effect of C-factor and light-curing protocol on gap formation in composite resin restorations. Material and METHODS: Cylindrical cavities with 5.0 mm diameter and three different depths (A=1.0, B=2.0 and C=3.0 mm) were prepared on the occlusal surface of 30 human molars and restored in a single increment with P 60. The composite resin was light-cured according to two protocols: standard - 850 mW/cm² / 20 s and gradual - 100 up to 1000 mW/cm² / 10 s + 1000 mW/cm² / 10 s. After storage in distilled water (37°C/7 days), the restorations were cut into three slices in a buccolingual direction and the gap widths were analyzed using a 3D-scanning system. The data were submitted to ANOVA and Student-Newman-Keuls test (alpha=0.05). RESULTS: ANOVA detected a significant influence for the C-factor and light-curing protocol as independent factors, and for the double interaction C-factor vs. light-curing protocol. Cavities with higher C-factor presented the highest gap formation. The gradual light-curing protocol led to smaller gap formation at cavity interfaces. CONCLUSIONS: The findings of this study suggest that the C-factor played an essential role in gap formation. The gradual light-curing protocol may allow relaxation of composite resin restoration during polymerization reaction