The effect of the process parameters in the planing processes on the surface roughness of cherry and pear woods

In this study, the effects of the process parameters in the planing processes on the surface roughness were investigated. For this purpose, the experimental samples of cherry (Prunus avium L.) and pear (Pirus communis L.) wood species, which are commonly used in the Turkish decoration industry, were prepared. In preparing the experimental samples, the wood was planed tangentially and radially to the annual rings at a cutting depth of 1.4 mm in a milling machine with 4 blades 85 mm in diameter. The wood was planed into the direction of spindle rotation and in the direction against the spindle rotation at feed rates of 6, 9 and 12 m/min. The surface roughness values of the experimental samples were determined by using a stylus-type profilometer according to the ISO 4287 standards. The surface roughness was evaluated according to the Ra, Rz and Ry principles, which were three basic parameters of the determination method for surface roughness. According to the results, when the planing parameters were differentiated, the obtained surface roughness values also acquired a different character. The feed direction of work pieces for planing in the direction of spindle rotation was lower than the feed direction in the opposite to spindle rotation for the surface roughness.Keywords: Surface Roughness, Planing, Cherry, Pear

Experimental and numerical evaluation of the compression behaviour of GFRP-wrapped infill materials

Glass Fibre Reinforced Polymer (GFRP) composite wrap has become an effective repair system for deteriorated structural columns. It is essential to provide an infill material in the gap between the retrofitted column and the GFRP wrap. So, the properties of the infill material can significantly influence the contribution of these wraps and thus, can affect the overall performance of the retrofitted structure. However, the research on the effect of GFRP confinement on infill materials with various properties is still limited. This study explores the effectiveness of the GFRP wrapping system and its contribution to the axial compression behaviour of concrete, grout and epoxy infill materials. A total of 18 unconfined and GFRP-wrapped cylindrical columns were cast and tested under concentric axial compression loading. A finite element (FE) modelling was implemented using ABAQUS software to analyse the compression behaviour of GFRP-wrapped infill materials. The experimental results demonstrated that the confinement effect of the GFRP wrapping system is highly influenced by the properties of the infill material. The compressive strength and modulus of elasticity significantly increased due to GFRP wrapping by 149 % and 77 %, respectively for concrete infill, and by 40 % and 72 %, respectively for grout infill whereas negligible confinement efficiency observed in wrapped epoxy infill. The FE analyses showed a good correlation with the experimental results in predicting the overall compressive behaviour of the various infill materials. This study demonstrates valuable insights on the confinement effect of GFRP wraps in the repair of columns involving infill materials which therefore could be employed to better understand the overall behaviour of columns retrofitted with GFRP wrapping systems

Unilateral congenital elongation of the cervical part of the internal carotid artery with kinking and looping: two case reports and review of the literature

Unilateral and bilateral variation in the course and elongation of the cervical (extracranial) part of the internal carotid artery (ICA) leading to its tortuosity, kinking and coiling or looping is not a rare condition, which could be caused by both embryological and acquired factors. Patients with such variations may be asymptomatic in some cases; in others, they can develop cerebrovascular symptoms due to carotid stenosis affecting cerebral circulation. The risk of transient ischemic attacks in patients with carotid stenosis is high and its surgical correction is indicated for the prevention of ischemic stroke. Detection of developmental variations of the ICA and evaluation of its stenotic areas is very important for surgical interventions and involves specific diagnostic imaging techniques for vascular lesions including contrast arteriography, duplex ultrasonography and magnetic resonance angiography. Examination of obtained images in cases of unusual and complicated variations of vascular pattern of the ICA may lead to confusion in interpretation of data. Awareness about details and topographic anatomy of variations of the ICA may serve as a useful guide for both radiologists and vascular surgeons. It may help to prevent diagnostic errors, influence surgical tactics and interventional procedures and avoid complications during the head and neck surgery. Our present study was conducted with a purpose of updating data about developmental variations of the ICA. Dissections of the main neurovascular bundle of the head and neck were performed on a total 14 human adult cadavers (10 – Africans: 7 males & 3 females and 4 – East Indians: all males). Two cases of unilateral congenital elongation of the cervical part of the ICA with kinking and looping and carotid stenoses were found only in African males. Here we present their detailed case reports with review of the literature

Behavior of FRP-confined normal- and high-strength concrete under cyclic axial compression

An important application of fiber-reinforced polymer (FRP) composites is as a confining material for concrete, both in the seismic retrofit of existing reinforced concrete columns and in the construction of concrete-filled FRP tubes as earthquake-resistant columns in new construction. The reliable design of these structural members against earthquake-induced forces necessitates a clear understanding of the stress-strain behavior of FRP-confined concrete under load cycles. This paper presents the results of an experimental study on the behavior of FRP-confined normal- and high-strength concrete under axial compression. A total of 24 aramid and carbon FRP-confined concrete cylinders with different concrete strengths and FRP jacket thicknesses were tested under monotonic and cyclic loading. Examination of the test results has led to a number of significant conclusions in regards to both the trend and ultimate condition of the axial stress-strain behavior of FRP-confined concrete. These results are presented, and a discussion is provided on the influence of the main test parameters in the observed behaviors. The results are also compared with two existing cyclic axial stress-strain models for FRP-confined concrete. © 2012 American Society of Civil Engineers.Togay Ozbakkaloglu and Emre Aki

Axial compressive behavior of FRP-confined concrete: Experimental test database and a new design-oriented model

A large number of experimental studies have been conducted over the last two decades to understand the behavior of FRP-confined concrete columns. This paper presents a comprehensive test database constructed from the results of axial compression tests on 832 circular FRP-confined concrete specimens published in the literature. The database was assembled through an extensive review of the literature that covered 3042 test results from 253 experimental studies published between 1991 and the middle of 2013. The suitability of the results for the database was determined using carefully chosen selection criteria to ensure a reliable database. This database brings reliable test results of FRP-confined concrete together to form a unified framework for future reference. Close examination of the test results reported in the database led to a number of important observations on the influence of important parameters on the behavior of FRP-confined concrete. A new design-oriented model that was developed to quantify these observations is presented in the final part of the paper. It is shown that the predictions of the proposed model are in close agreement with the test results and the model provides improved predictions of the ultimate conditions of FRP-confined concrete compared to any of the existing models. © 2013 Elsevier Ltd. All rights reserved.Togay Ozbakkaloglu, Jian C. Li

Influence of Size and Slenderness on Compressive Strain Softening of Confined and Unconfined Concrete

It is generally accepted that the postpeak strain-softening behavior of concrete in compression is a localized phenomenon that occurs mainly in the compression damage zone. Accurate quantification of the size and slenderness effects on the postpeak behavior of concrete, therefore, depends on the accurate quantification of the inelastic deformations that occur in the compression damage zone. In this study, a novel approach is proposed to separate the two inelastic deformation components, known as the localized crack deformation and the deformation caused by the inelastic strain in the compression damage zone, from experimental stress-strain curves. This new approach allows the utilization of existing test results in the published literature in the model development. Based on two comprehensive experimental databases of confined and unconfined concretes covering a wide range of concrete strengths, a constitutive model for predicting the strain-softening behavior of confined and unconfined concretes is proposed

Lateral Strain-to-Axial Strain Relationship of Confined Concrete

The use of fiber-reinforced polymers (FRP) has become widely accepted engineering practice for strengthening reinforced concrete members. It is well established that lateral confinement of concrete with FRP composites can significantly enhance its strength and ductility. As the confinement pressure generated by FRP on the confined concrete depends on the lateral expansion of concrete, the mechanism of concrete expansion inside the FRP shell is of significant interest. A review of the existing stress-strain models of FRP-confined concrete revealed the need for a model that accurately predicts the dilation characteristic of confined concrete as it provides the essential link between the response of the concrete core and the passive confinement mechanism of the FRP shell. It is also understood that knowledge established from the research area of actively confined concrete can be employed in the development of a model applicable for both FRP-confined and actively confined concretes. Based on a large number of experimental test results of both FRP-confined and actively confined concretes, a generic model is proposed to describe the lateral strain-to-axial strain relationship of confined concrete. The instrumentation arrangements of the tested specimens have allowed for the lateral strain-axial strain relationships of confined concrete to be captured throughout the tests. The trend of the lateral strain-to-axial strain relationship of confined concrete is shown to be a function of the confining pressure, type of confining material and concrete strength. Assessment of models with the experimental databases showed that the predictions of the proposed model are well above existing models and in good agreement with the test results of both FRP-confined and actively confined concretes

Damage-Plasticity Model for FRP-Confined Normal-Strength and High-Strength Concrete

This paper presents a modified damage-plasticity model for fiber-reinforced polymer (FRP)-confined normal-strength and high-strength concrete (NSC and HSC). The proposed model is based on a concrete damage-plasticity model from the literature, which is improved through accurate incorporation of the effects of the confinement level, concrete strength, and nonlinear dilation behavior of FRP-confined concrete. The proposed model uses a new and accurate failure surface and flow rule that were established using a comprehensive and up-to-date experimental test database and it incorporates an analytical rupture strain model for the FRP jacket. Finite-element (FE) models incorporating the proposed damage-plasticity model are developed and validated for concretes having up to 110-MPa compressive strength confined by different types of FRP under a wide range of confining pressures. Comparisons with experimental results show that the model’s predictions of (1) axial stress-axial strain, (2) lateral strain-axial strain, (3) axial stress-volumetric strain, (4) plastic volumetric strain-axial plastic strain, and (5) plastic dilation angle-axial plastic strain relations are in good agreement with the test results of FRP-confined NSC and HSC. The accurate predictions of the compressive strength and ultimate axial strain of FRP-confined concrete were achieved by establishing the hardening/softening rule and flow rule based on the level of confining pressure and modeling the failure surface of the confined concrete by incorporating the effect of unconfined concrete strength