Applicability of empirical models for evaluation of stress ratio effect on the durability of fiber-reinforced creep rupture–susceptible composites
Fiber-reinforced polymer–matrix composites are known to exhibit loading rate- and time-dependent mechanical response. Their fatigue strength is determined by a complex interaction of damage processes governed by loading duration and cycle number. Apart from mechanistic approaches, a number of empirical models of various sophistication have been proposed to predict the durability of composites, differing in the amount of experimental data needed for their application. The accuracy of several such models is evaluated by comparing the prediction to the experimentally determined stress ratio effect on fatigue life of glass fiber-reinforced polyester–matrix composite. It is found that the accuracy of prediction generally improves with increasing the amount of test data needed for model calibration. However, the most accurate method of fatigue life estimation, among the selected ones, is by the modified Goodman diagram.
Experimental investigation and modeling of mean load effect on fatigue behavior of adhesively-bonded pultruded GFRP joints
The effect of mean load on the fatigue behavior of adhesively-bonded pultruded GFRP double-lap joints under constant amplitude loading was experimentally investigated. The joints were examined under nine different stress ratios (R) representing pure tension, compression, and combined tension-compression fatigue loading. A transition of the failure mode, from tensile to compressive, was observed as the mean load decreased from positive to negative values. The slope of the S-N curves derived for R-ratios with positive or negative mean load consistently decreased with increasing mean load. The highest load amplitude corresponded to the R-ratio where the transition of the fatigue failure mode occurred (R = -2). The characteristics of the constant life diagram developed for the examined bonded joints are thoroughly discussed. A phenomenological formulation was proposed and its accuracy evaluated by comparisons with the derived experimental data. The comparison of the new formulation with models commonly used for composite materials proved its higher accuracy that is achieved with less implementation effort. © 2012 Elsevier Ltd. All rights reserved.
Reference values for some haematological, haematochemical, and electrophoretic parameters in the Girgentana goat
The purpose of this study was to determine haematolog ical, haematochemical, and electrophoretic reference values for the Girgentana goat in order to form a basis for clinical interpretation. The study included 348 female Girgentana goats aged from 1 to 6 years. The animals were divided into 3 groups: goats aged 1-2 years (group A), goats aged 3-4 years (group B), and goats aged 5-6 years (group C). Blood samples were collected from each animal every morning at the same time (0800) by means of jugular venipuncture, and red blood cell (RBC), white blood cell (WBC), neutrophil (NEU), lymphocyte (LYM), monocyte (MONO), eosinophil (EOS), and basophil (BASO) counts, and haemoglobin (Hb), packed cell volume percent (PCV), mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH), mean corpuscular haemoglobin concentration (MCHC), and red cell distribution width (RDW) were recorded. Additionally, the concentration of some haematochemical parameters, including alanine-aminotransferase (ALT), aspartate-aminotransferase (AST), γ-glutamine-transferase (γ-GT), creatinine, β-hydroxybutyrate, urea, non- esterified fatty acids (NEFA), potassium, sodium, and chloride, and the electrophoretic profile (albumin, α1-globulins, α2-globulins, β-globulins, γ-globulins, total proteins and albumin:globulins ratio) were determined. Statistical analysis (one-way analysis of variance (ANOVA)), followed by Bonferroni's test, showed that there were significant differences only in RBC, MCV, EOS, ALT, AST, creatinine, γ-GT, sodium, urea, NEFA, γ-globulins, and the albumin:globulins ratio (P < 0.05 was considered statistically significant). The values determined in the present study contribute to the knowledge of the reference ranges for the Girgentana goat and can be used for monitoring health and disease diagnosis.