2-D strength prediction of single-row multi-bolted joints woven fabric kenaf composites

Implementation of multi-bolts arrangements in structures connections are commonplace in steel design to allow for joint efficiency and stronger connections. Woven fabric kenaf fibers are potentially used as reinforcement in composite materials due to excellent specific strength, renewability and less hazardous during handling as compared to commercial fibers. A two-dimensional Extended Finite Element Method (XFEM) framework of single-row multi-bolted joints has been developed to study the stress distribution and predict the joint bearing stress at failure. Stress distribution among adjacent bolts were compared along the hole boundary and net-tension plane, suggesting net-tension failure occurred at end-bolt. The predicted bearing strength from finite element modelling are validated against experimental framework. The testing series under investigated consists of four datasets from single-row 2 bolts and 3 bolts single-lap joints. Current study showed that the XFEM models demonstrated good agreements with the experimental results

3-D modelling of single-lap multi-bolted joints under quasi-static conditions

Multi-bolted joint configurations are commonly used in joining different parts in various engineering sectors, ability of bolts to transfer by-pass stress to adjacent bolts prone of net-tension to occur compared to singlebolt joint configurations. There is bearing-bypass envelope has been proposed but due to complexities in bearing damage leading to difficulties in predicting failure modes. More recently, strength prediction works in composite structures are carried out within finite element framework to take into advantage of advanced computing technology. Current work implemented a three-dimensional Extended Finite Element Method (XFEM) framework of single-row multi-bolted joints to predict the bearing stress at failure, validated against experimental datasets. A testing series comprised of different clamping load and number of bolts in a single row. All testing series failed in net-tension failure mode, suggesting prominent effect from stress concentration. Crack initiation and propagations shows similarity within XFEM and experimental observations. Good agreements were found (less than 10% discrepancy) due to ability in 3-D modelling to capture effect of bolt load and frictional load transfer

Strength predictions of multi-bolted joints in woven fabric kenaf composite plates with different configurations using xfem frameworks

Multi-bolted joints are designed as joining technique to provide efficiency in assembling different structure parts; however the ability of neighboring bolts to transfer by-pass stress susceptible to net-tension failure occurrence. More recently, strength prediction works in composite structures are carried out within finite element framework to utilize advantage of advanced computing technology. Current work implemented a three-dimensional Extended Finite Element Method (XFEM) framework of multi-bolted joints configurations in variations lay-ups to determine failure load, validated against experimental datasets. Other testing parameters investigated comprised of different bolts configurations and plate geometries. Visual tracking from XFEM contour found that crack initiation and propagations are consistent with experimental observations. Better agreements were found in nonstaggered configurations with largest discrepancy of approximately 30%, mostly gives less than 15%. Besides, combination of cross-ply and thicker plates promotes better predictions due to larger repetitive plies as current work implemented smeared-out properties within its constitutive model

XFEM Modelling of Multi-holes Plate with Single-row and Staggered Holes Configurations

Joint efficiency is the key to composite structures assembly design, good structures response is dependent upon multi-holes behavior as subjected to remote loading. Current benchmarking work were following experimental testing series taken from literature on multi-holes problem. Eleven multi-hole configurations were investigated with various pitch and gage distance of staggered holes and non-staggered holes (single-row holes). Various failure modes were exhibited, most staggered holes demonstrates staggered crack path but non-staggered holes series displayed crack path along net-section plane. Stress distribution were carried out and good agreement were exhibited in experimental observation as reported in the respective literature. Consequently, strength prediction work were carried out under quasi-static loading, most showed discrepancy between 8% -31%, better prediction were exhibited in thicker and non-staggered holes plate combinations

Investigation on the growth and luminescence spectra of congruent Linbo3 crystal obtained in air atmosphere by Czochralski Method

Single crystal of Congruent LiNbO3 (CLN) was grown by the Czochralski method in an air atmosphere with ADC (Automatic Diameter Control) r.f. heating. In this study, the optimum conditions required to grow high quality CLN single crystal are described. The high quality CLN single crystal with growth direction of ?001? was produced by effective control of growth conditions. The luminescence spectra from LiNbO3 is due to change?transfer in the niobate octahedron, and is strongly affected by the concentration of Li vacancies. For CLN single crystal at room temperature under 300nm wavelength excitation, the emission maximum is 760 nm. There are significant differences between the intensity of component emission band in the X, Y and Z cut crystals. Luminescence decay times and intensity variations gives a qualitative measure of both purity and crystal quality

XFEM modelling in multi-bolted joints using a unified bolt preload

Multi-bolted joints are adopted and designed to provide efficient load transfer within assembled engineering parts. Bearing failure is favorable during design phase due to more progressive failure mode, however, ability of by-pass stress to be transferred to adjacent bolts in multi-bolted joints prone to catastrophic net-tension failure. Former approach known as equivalent spring stiffness (ESS) was proposed but it requires experimental sliding load value. This has led to semi-empirical approach to require experimental set-up than incorporating a generic bolt preload value. This paper aims to provide a unified bolt preload (UBP) value to be implemented in each bolt independent upon plate properties and bolts arrangements. Strength prediction were taken place by 3-D Extended Finite Element Method (XFEM) framework of various staggered and non-staggered arrangements to include various lay-ups types and plate thickness. The failure loads predictions in each testing series were investigated and then validated against experimental datasets and also compared with previous technique (ESS approach). Crack patterns and failure modes from this approach were consistent with experimental observations, where net-tension failures were observed within all testing series. Less good prediction compared to from ESS technique, partly due to semi-empirical nature in former approach. Nevertheless, reasonable agreement in UBP technique with experimental datasets were obtained (average discrepancy of approximately 20%)