Does lower lifetime fluoridation exposure explain why people outside capital cities have poor clinical oral health?

Abstract Background Australians outside state capital cities have greater caries experience than their counterparts in capital cities. We hypothesized that differing water fluoridation exposure was associated with this disparity. Methods Data were the 2004–06 Australian National Survey of Adult Oral Health. Examiners measured participant decayed, missing and filled teeth and DMFT Index, and lifetime fluoridation exposure was quantified. Multivariable linear regression models estimated differences in caries experience between capital city residents and others, with and without adjustment for fluoridation exposure. Results There was greater mean lifetime fluoridation exposure in state capital cities (59.1%, 95% confidence interval = 56.9, 61.4) than outside capital cities (42.3, confidence interval = 36.9, 47.6). People located outside capital city areas had differing sociodemographic characteristics and dental visiting patterns, and a higher mean DMFT (capital cities = 12.9, non‐capital cities = 14.3, p = 0.02), than people from capital cities. After adjustment for sociodemographic characteristics and dental visits, DMFT of people living in capital cities was less than non‐capital city residents (regression coefficient = 0.8, p = 0.01). The disparity was no longer statistically significant (regression coefficient = 0.6, p = 0.09) after additional adjustment for fluoridation exposure

Failure Modelling of Woven GFRP Bolted Joints under Quasi-Static Loading

Current work concentrates in modelling failure and damage of various woven fabric reinforcement system taken from selected literatures. Experimental observations under quasi-static loading revealed that initial failure occurs at notch vicinity consist of one or combinations of matrix cracking, splitting and laminate de-lamination. The crack then propagated along net-section of distance of about one notch radius size, which thereafter occurrence usually corresponds to catastrophic failures that seen significant tow fractures. The distance of cracked zone signifies ultimate material failure usually referred as “effective damage zone” that useful to be implemented within fracture mechanics concept. These complex morphologies mechanisms can be represented by implementing physically-based constitutive model. Series works of notched woven fabric composite systems plate were implemented within two-dimensional extended finite element method (XFEM) framework were carried out by implementing constitutive models based on basic material properties data of respective system. Good agreement is shown in comparison with experimental data in various and other closed-form approaches composite fabric systems

The Static Failure of Adhesively Bonded Metal Laminate Structures: A Cohesive Zone Approach

Data on distribution, ecology, biomass, recruitment, growth, mortality and productivity of the West African bloody cockle Anadara senilis were collected at the Banc d'Aguuin, Mauritania, in early 1985 and 1986. Ash-free dry weight appeared to be correlated best with shell height. A. senilis was abundant on the tidal flats of landlocked coastal bays, but nearly absent on the tidal flats bordering the open sea. The average biomass for the entire area of tidal flats was estimated at 5.5 g·m−2 ash-free dry weight. The A. senilis population appeared to consist mainly of 10 to 20-year-old individuals, showing a very slow growth and a production: biomass ratio of about 0.02 y−1. Recruitment appeared negligible and mortality was estimated to be about 10% per year. Oystercatchers (Haematopus ostralegus), the gastropod Cymbium cymbium and unknown fish species were responsible for a large share of this. The distinction of annual growth marks permitted the assessment of year-class strength, which appeared to be correlated with the average discharge of the river Senegal. This may be explained by assuming that year-class strength and river discharge both are correlated with rainfall at the Banc d'Arguin.

Fracture mechanics and damage mechanics based fatigue lifetime prediction of adhesively bonded joints subjected to variable amplitude fatigue

The first part of the paper describes an investigation into the behaviour of adhesively bonded single lap joints (SLJs) subjected to various types of variable amplitude fatigue (VAF) loading. It was seen that a small proportion of fatigue cycles at higher fatigue loads could result in a significant reduction in the fatigue life. Palmgren-Miner's damage sum tended to be less than 1, indicating damage accelerative load interaction effects. In the second part of the paper, fracture mechanics (FM) and damage mechanics (DM) approaches are used to predict the fatigue lifetime for these joints. Two FM based approaches were investigated, which differed with respect to the cycle counting procedure, however, both approaches were found to under-predict the fatigue lifetime for all the types of spectra used. This was attributed to the inability of the FM based models to simulate the crack initiation phase. A DM based approach was then used with a power law relationship between equivalent plastic strain and the damage rate. Good predictions were found for most of the spectra, with a tendency to over-predict the fatigue life

Unified methodology for the prediction of the fatigue behaviour of adhesively bonded joints

A unified model is proposed to predict the fatigue behaviour of adhesively bonded joints. The model is based on a damage mechanics approach, wherein the evolution of fatigue damage in the adhesive is defined as a power law function of the micro-plastic strain. The model is implemented as an external subroutine for commercial finite element analysis software. Three dimensional damage evolution and crack propagation were simulated using this method and an element deletion technique was employed to represent crack propagation. The model was able to predict the damage evolution, crack initiation and propagation lives, strength and stiffness degradation and the backface strain during fatigue loading. Hence the model is able to unify previous approaches based on total life, strength or stiffness wearout, backface strain monitoring and crack initiation and propagation modelling. A comparison was made with experimental results for an epoxy bonded aluminium single lap joint and a good match was found

Modelling cyclic moisture uptake in an epoxy adhesive

This paper presents a methodology for predicting moisture concentration in an epoxy adhesive under cyclic moisture absorption-desorption conditions. The diffusion characteristics of the adhesive were determined by gravimetric experiments under cyclic moisture conditions and the dependence of diffusion coefficient and saturated mass uptake on moisture history was determined. Non-Fickian moisture absorption was observed during absorption cycles while moisture desorption remained Fickian. The diffusion coefficient and saturated moisture content showed variation with absorption-desorption cycling. A finite element-based methodology incorporating moisture history was developed to predict the cyclic moisture concentration. A comparison is made between the new modelling methodology and a similar method that neglects the moisture history dependence. It was seen that the concentration predictions based on non-history dependent diffusion characteristics resulted in over-prediction of the moisture concentration in cyclic conditioning of adhesive joints. The proposed method serves as the first step in the formulation of a general methodology to predict the moisture dependent degradation and failure in adhesives

Moisture absorption-desorption effects in adhesive joints

This paper presents a study of moisture absorption-desorption effects in single lap adhesive joints. Experiments were carried out to characterise the moisture uptake of the single part epoxide adhesive, FM73. Tensile testing of single lap joints manufactured from aluminium alloy 2024 T3 and O and FM73 adhesive was carried out after the joints were exposed to different conditioning environments. The experimental results revealed that the failure strength of the single lap joints with 2024 T3 adherends progressively degraded with time when conditioned at 50°C, immersed in water. However, the joint strength almost completely recovered after moisture was desorbed. The single lap joints with 2024 O adherends showed decreased strength for 28 days of conditioning, after which strength recovered, reaching a plateau after 56 days. Again, strength almost completely recovered on desorption of moisture. The strength recovery of the joints, after desorption of moisture, showed that the degradation of the adhesive was largely reversible. Analysis of the failure surfaces revealed that the dry joints failed cohesively in the adhesive layer and that the failure path moved towards the interface after conditioning. The failure mode then reverted back to cohesive failure after moisture desorption

Strength Prediction of Notched Woven Composite Plates using a Cohesive Zone Approach

Abstract. The present paper is concerned with modelling damage and fracture in notched woven fabric composites. Previous experimental work has shown that damage at a notch in a variety of GFRP and CFRP composites based on woven fabric reinforcement comprises matrix damage and fibre tow fracture along the plane of maximum stress. It is these experimental observations that inform the failure modelling developed here, in which a cohesive zone approach is used within a 2-D finite element framework. The cohesive zone parameters are based on previously reported experimental measurements for the strength and toughness of the woven fabric materials under investigation. The approach is shown to provide predictions of notched strength that are in very good agreement with experimental results from the literature for a range of GFRP and CFRP woven fabric systems