Influence of z-pinning on the buckling of composite laminates under edge-wise compression

Z-pinning is a newly developed technique to enhance the strength of composite laminates in the thickness direction. Recent experimental and theoretical studies have shown that z-pins significantly improve mode I and mode II fracture toughness. In practice, buckling accompanying delamination is a typical failure mode in laminated composite structures. For a complete understanding of the z-pinning technique towards improvements of the overall mechanical properties of laminated composites, a numerical model is developed in this paper to investigate the influence of z-pins on the buckling composite laminates with initial delaminations under edge-wise compression. The numerical results indicate that z-pinning can indeed effectively increase the compressive strength of the composite laminates provided that the initial imperfection is within a certain range. The magnitude of the improvement is consistent with available experimental data.

Numerical study of the mode I delamination toughness of Z-pinned laminates

A finite element (FE) model is developed to investigate mode I delamination toughness of z-pin reinforced composite laminates. The z-pin pullout process is simulated by the deformation of a set of non-linear springs. A critical crack opening displacement (COD) criterion is used to simulate crack growth in a double-cantilever-beam (DCB) made of z-pinned laminates. The toughness of the structure is quantified by the energy release rate, which is calculated using the contour integral method. The FE model is verified for both unpinned and z-pinned laminates. Predicted loading forces from FE analysis are compared to available test data. Good agreement is achieved. Our numerical results indicate that z-pins can greatly increase the mode I delamination toughness of the composite laminates. The influence of design parameters on the toughness enhancement of z-pinned laminates is also investigated, which provides important information to optimise and improve the z-pinning technique.

Mode II delamination toughness of Z-pinned laminates

Mode II delamination toughness of z-pin reinforced composite laminates is investigated using finite element (FE) method. The z-pin pullout process is simulated by the deformation and breakage of non-linear springs. A critical shear stress criterion based on linear elastic fracture mechanics is used to simulate crack growth in an end-notched-flexure (ENF) beam made of z-pinned laminates. The mode II toughness is quantified by the potential energy release rate calculated using the contour integral method. This FE model is verified for an unpinned ENF composite beam. Numerical results obtained indicate that z-pins can significantly increase the mode II delamination toughness of composite laminate. The effects of design variables on the toughness enhancement of z-pinned laminates are also studied, which provides an important technological base and useful data to optimize and improve the z-pinning technique.

Experimental study on effect of loading rate on mode I delamination of z-pin reinforced laminates

This paper presents an experimental investigation on mode I delamination of z-pinned double-cantilever-beams (DCB) and associate z-pin bridging mechanisms. Tests were performed with three types of samples: big-pin with an areal density of 2%, small-pin with an areal density of 2% and small-pin with an areal density of 0.5%. The loading rates for each type of samples were set at 1 mm/min and 100 mm/min. Comparison of fracture load under different loading rates shows the rate effects on delamination crack opening and delamination growth. Optical micrographs of z-pins after pullout were also presented to identify the bridging mechanisms of z-pins under different loading rates.

Z-pin bridging in composite laminates and some related problems

This paper reviews our recent studies on z-pinning of composite laminates. The contents include theoretical, numerical and experimental studies on the Mode I and Mode II z-pinned delamination growth and the corresponding bridging laws. Test methods to evaluate the z-pin bridging law will be discussed. Comparisons of experimental results and theoretical predictions for the z-pinned double-cantilever-beam (DCB) subjected to mode I delamination with a pre-determined bridging law are provided to confirm the reliability of the methods. A parametric study by finite element method (FEM) is presented for both Mode I and Mode II z-pinned delaminations. In addition, the effect of loading rate on z-pinned DCB delamination and the bridging effect of z-pinning on the buckling of composite laminates are also given.

Characterisation and impedance spectroscopy of substituted Li1.3Al0.3Ti1.7(PO4)3−x(ZO4)x (Z=V, Nb) ceramics*1

Lithium ion conducting ceramics based on the lithium aluminium titanium phosphate (LATP) NASICON structure have been prepared with various substitutions of the phosphorous. The effect of the processing method has been shown to be the key factor in determining the conductivity, both bulk and grain boundary, as well as the conductivity trends observed as a function of substitution.

Parental use of restrictive feeding practices and child BMI z-score. A 3-year prospective cohort study

This study examines associations between parental feeding restriction at baseline and child body mass index (BMI) z-score at 3-year follow-up. Parents of 204 5–6-year-old and 188 10–12-year-old children completed the Child Feeding Questionnaire at baseline (2002/3). In 2002/3 and 2005/6, children's BMI z-score was calculated from measured height and weight. Analyses were stratified by age-group. The association of follow-up zBMI and baseline feeding restriction score was explored using (i) linear regression with adjustment for baseline zBMI and (ii) with further adjustments for baseline maternal BMI, maternal education level and child sex. Baseline restriction was associated with follow-up zBMI at 3 years in 5–6-year-old children and was largely unchanged when adjusting for child sex, maternal BMI and education. Restriction was not associated with follow-up zBMI in 10–12-year-old children. This longitudinal study adds important depth to our understanding of associations between restrictive feeding and change in zBMI, suggesting that restriction of energy-dense foods and drinks may be protective of unhealthy weight gain in younger children but may have no effect among older children. These findings support a reconsideration of the notion that restriction is likely to result in increased child weight.

Investigation of the performance of the menifocal Z gas-permeable bifocal contact lens during continuous wear

Purpose. The Menifocal Z is an alternating vision, concentric, bifocal gas-permeable (GP) contact lens; center distance is connected to near periphery by a smooth transition zone. The lens is produced using tisilfocon A (Menicon Z material), which is approved for up to 30 days of continuous wear (CW). The aim of this study was to evaluate the clinical performance of the Menifocal Z when worn for up to 30 days of CW for 6 months.

Methods. Thirty-five existing GP lens wearers were enrolled in the study. Subjects were fitted with Menifocal Z lenses and follow-up visits were conducted after 2 weeks of daily wear and 1 day, 1 week, 6 weeks, 3 and 6 months of CW. A range of objective and subjective clinical performance measures were assessed, including distance and near visual acuity, the physiological response to CW, and subjective evaluation of vision and comfort.

Results. Twenty-seven subjects (77%) completed the study and eight (23%) discontinued: five (14%) as a result of lens-related problems (four vision, one comfort) and three (9%) as a result of non-lens related reasons. Average CW time achieved by the subjects was 22 ± 2 days. Mean binocular logarithm of the minimum angle of resolution (logMAR) acuities at 6 months were: high contrast distance 0.03 (20/20-), low contrast distance 0.63 (20/80-), and high contrast near 0.26 (20/25, N4). Adverse responses and lens binding were minimal, and there were no significant increases in corneal staining, corneal vascularization, or superior palpebral conjunctival papillae over time (p > 0.05). Problems with night vision (distance and near) with the lenses were the most common difficulties reported by the subjects.

Conclusions. The Menifocal Z appears to be a promising option for presbyopic vision correction, providing successful correction of distance and near vision in a group of experienced GP lens wearers. The hyper Dk tisilfocon A (Menicon Z) material allowed for safe wear of the lenses on a CW basis.

Whole grain consumption is inversely associated with BMI Z-score in rural school-aged children

Objective To examine the relationship between intake of whole grains and BMI Z-score in rural children.

Design General linear models and logistic regression were used to examine the cross-sectional associations between whole grain intake and BMI Z-score, prevalence and odds ratios of overweight and obesity. Dietary intake was assessed using the Block Food Screener for ages 2–17 years. Children were classified into three categories according to servings of whole grain intake: <1·0 serving/d, 1·0–1·5 servings/d and >1·5 servings/d.

Setting The CHANGE (Creating Healthy, Active and Nurturing Growing-up Environments) study, an obesity prevention intervention in elementary schools in eight rural US communities in California, Mississippi, Kentucky and South Carolina.

Subjects Seven hundred and ninety-two children attending 3rd–6th grade.

Results After adjusting for age, sex, race/ethnicity, physical activity and state of residence, whole grain intake was inversely associated with BMI Z-score (0·90 v. 0·61 in the lowest v. the highest whole grain intake category; P trend = 0·01). Children who consumed >1·5 servings of whole grains/d had a 40 % lower risk of being obese (OR = 0·60; 95 % CI 0·38, 0·95, P = 0·02) compared with children who consumed <1·0 serving/d. Further adjustment for potential dietary predictors of body weight (fruit, vegetable and dairy intakes) did not change the observed associations.

Conclusions Increasing the intake of whole grains as part of an overall healthy lifestyle may be beneficial for children to achieve and maintain a healthy weight.

Socio-demographic lifestyle and psychological predictors of benzodiazepine and z-hypnotic use patterns

Aims : Risk and demographic factors for benzodiazepine and z-hypnotic use are incompletely understood. The aim of the paper was therefore to investigate socio-demographic, lifestyle and psychological factors predicting onset and differential pattern of prescribed benzodiazepine and z-hypnotic use in a Norwegian population sample.

Methods : This retrospective cohort study obtained socio-demographic, psychological and lifestyle variables from the Nord-Trøndelag Health Study. Information about benzodiazepine prescriptions from the Norwegian prescription database were linked to epidemiological questionnaire data. Benzodiazepine use was classified into single-period, intermittent and chronic use, and high dose use was defined as being prescribed a yearly average above 180 daily defined doses.

Results : Older age, sleep difficulties and smoking were positively associated with all patterns of benzodiazepine use. Male gender was related to a reduced risk of all patterns of use, whereas educational achievement was negatively associated with single-period use. Alcohol consumption, anxiety and tension were positively related to intermittent and chronic use, while exercise was negatively related to chronic use. Smoking, sleep difficulties and old age were positively associated with prescriptions of high benzodiazepine doses, while exercise was associated with lower doses.

Conclusions : Patterns of prescribed benzodiazepine use are linked to demographic, lifestyle and clinical variables. Non-pharmacological treatment for sleep difficulties and smoking cessation may reduce the risk of chronic benzodiazepine use.