Influence of Tableting Forces and Lubricant Concentration on the Adhesion Strength in Complex Layer Tablets

The strength of adhesion in complex two-layer tablets is assessed using statistical methods with respect to the applied tableting forces for the first layer and for applying the second layer on the first, as well as regarding the fraction of the lubricant. These results, obtained on a single-punch tablet press, are compared with the results for three-layer tablets produced on a rotary press at production scale. The strongest negative influence on adhesion strength was exerted by the amount of lubricant in the central layer. As expected, compression forces for central-layer tableting also had a negative effect, whereas the compression forces for complex layer tableting exerted a positive effect on layer adhesion. The validity of the derived model equation was proved by experiments: It was shown that the adhesion strength in complex layer tablets produced in production scale can be predicted from laboratory-scale experiments. This makes optimization of the formulation and parameter settings at an early stage of development possible.     

Influence of palm oil fuel ash on ultimate flexural and uniaxial tensile strength of green ultra-high performance fiber reinforced cementitious composites

This study focuses on the measurement of the ultimate flexural and tensile strength of GUSMRC, a new class of green ultra-high performance fiber reinforced cementitious composites (GUHPFRCCs) in which 75% of the volume contains ultrafine palm oil fuel ash (UPOFA). This green concrete is currently under development at the Universiti Sains Malaysia (GUSMRC). The main objective of this study is to investigate the potential of UPOFA as a partial binder replacement for the ultimate flexural and uniaxial tensile strength of GUSMRC mixtures. Results showed that UPOFA enhances the flexural and uniaxial tensile responses of fresh UHPFRCCs. The highest flexural and uniaxial tensile strength values at the 50% replacement level after 28 days were at 42.38 MPa and 13.35 MPa, respectively, indicating the potential of utilizing UPOFA as an efficient pozzolanic mineral admixture for the production of GUSMRC with superior engineering properties.     

Direct tensile tests on particulate agglomerates for the determination of tensile strength and interparticle bond forces

The importance of direct tensile tests on solid and capillary bonded particulate agglomerates is investigated and compared to compression test measurements. The properties of wet agglomerates are varied by changing the contact angle by means of functionalization of the particle surface. Process conditions are considered by variation of ambient humidity. A qualitative evaluation of the results is performed by analyzing the measured force distance curves of different tensile tests. The results are quantitatively evaluated by calculating the breakage strength, mass related breakage energy and breakage probability showing that the ratio between tensile and compressive tests is highly dependent on the adjusted parameters. Next to the process parameter effect, also the influence of agglomerate size is considered. Tensile strength data are used to estimate the single bond forces between the primary particles of the agglomerates. Tensile and compressive test results are compared to numerical results (DEM) of agglomerate breakage using an elastic stiff bond model.     

Influence of water-soluble polymers on the in vitro performance of floating mucoadhesive tablets containing metformin

Context: The in vitro performance of floating mucoadhesive metformin tablets was optimized using different polymer ratios of polyvinylpyrrolidone (PVP) tamarind seed gum (TSG) and hydroxypropylmethylcellulose (HPMC).

Objective: The objectives of this investigation were to investigate the combinatorial effects of PVP, TSG and HPMC; to study the work of adhesion measured on stainless steel (W_ss) and on rabbit gastric mucosa (W_gm); and a comparison of hydrophilic and more hydrophobic tablets.

Material and methods: In vitro performance was measured as tablet hardness (H), tablet floating lag time (FLT), time needed to release 60% of drug content (t_60%), swelling thickness (S), W_ss and W_gm. To compare the effects, a simplex lattice mixture design was used.

Results and discussion: H, FLT, W_ss and W_gm were found dependent on polymer ratio. H was increased when PVP ratio was increased. FLT, W_ss and W_gm were increased when HPMC ratio was increased. The p value for the lack of fit for all models were greater than 0.05. An approximate linear correlation between W_gm and W_ss was established (R²?=?0.71). The tablets containing PVP resulted in larger H, shorter FLT and t_60%, whereas W_ss and W_gm were enhanced.

Conclusion: The different in vitro performance of tablets containing different water-soluble polymers could be explained partially by the differences in the hydrophilic properties of the polymers and the ability of PVP to interact with HPMC or TSG. An equation established is used to conclude mucoadhesion based on adhesion measurements on stainless steel.     

Influence of winding angle on the strength and deformation of filament-wound composite tubes subjected to uniaxial and biaxial loads

Experimental data are presented to show the effects of winding angle on the strength of 100 mm diameter, 1 mm thick, filament wound E-glass fibre reinforced epoxy resin tubes tested under various combinations of internal pressure and axial tension or compression. Leakage and fracture strength envelopes are presented for ±45°, ±55° and ±75° winding angle tubes subjected to a wide range of different biaxial membrane stress states. Strengths range from 30 to 1250 MPa. Axial compression test results for tubes with wall thicknesses ranging from 1 to 3·6 mm establish the influence of shell buckling. Stress/strain curves up to fracture under three different types of loading show the effects of the winding angle on elastic constants and on nonlinear stress strain behaviour.     

Effects of different sealing conditions on the seal strength of polypropylene films coated with a bio‐based thin layer

This paper presents the results of an investigation through the design of experiment technique regarding the influence of temperature, dwell time and bar pressure on the heat seal strength of oriented polypropylene films coated with a gelatin‐based thin layer. This chemometric approach allowed achieving a thorough understanding of the effect of each independent factor on the two different responses (maximum force and strain energy) considered in this work as a measure of the strength necessary to break the bond across the sealed interface. Surprisingly, the factor affecting both responses the most was the bar pressure rather than the sealing temperature. Moreover, whereas the bar pressure negatively affected the seal strength of coated polypropylene films, the sealing temperature had a positive effect. Dwell time did not have any significant influence as a main factor, while influencing negatively the seal strength as an interaction term (i.e. time × pressure), together with the further interaction temperature × pressure. The mathematical models obtained for the two responses provided different results in terms of fitting capability (R²) and prediction ability (Q²). In particular, for the maximum force response, R² and Q² were equal to 0.571 and 0.405, respectively, whereas the model supporting the strain energy response gave R² = 0.932 and Q² = 0.937, highlighting that for quantifying the seal strength, the energy necessary to break a seal is a better measure than the maximum force. The highest seal strength values obtained during this work were of 0.6615 N and 19.6 N·mm for maximum force and strain energy, respectively. Copyright © 2009 John Wiley & Sons, Ltd.     

Effect of openings on the behaviour and strength of R/C beams in shear

The effects of introducing a transverse opening on the behaviour and strength of reinforced concrete beams under predominant shear are presented and discussed in this paper. On the basis of observed structural response, some guidelines are suggested to classify the opening as “large” or “small”. For small openings, two types of diagonal tension failure have been identified, and a method of design using the current codes of practice is proposed. The method is illustrated by a numerical example.     

Influence of fibre length and concentration on the properties of glass fibre-reinforced polypropylene: Part 3. Strength and strain at failure

In this report we present the results from the third part of a study on the influence of fibre length (0.1–50 mm) and concentration (3–60% w/w) on the properties of glass fibre-reinforced polypropylene laminates. These laminates were prepared in the laboratory using a wet deposition method and compared with samples prepared on a commercial melt impregnation GMT line. We found that laminate tensile strength increased linearly with fibre concentration up to 60% w/w. Laminate strength was also found to increase with increasing fibre length. At high values of fibre length (> 3–6 mm) the strength reached a plateau level which was directly dependent on fibre content. The matrix molecular weight appeared to have little direct influence on the level of laminate strength. However, the glass fibre sizing compatibility was found to have a strong effect on the tensile strength of both laboratory made wet deposited laminates and commercially prepared GMTs. The tensile strength of the GMT samples also showed a clear correlation with the measured fibre strength. A modified version of the Kelly-Tyson model gave calculated values of laminate strength which correlated well with the experimental data. We propose that the tensile strength of these laminates is governed by the properties of the fibres which have an orientation close to parallel with the loading direction.     

Influence of T-stress, cohesive strength and yield strength on the competition between decohesion and plastic flow in a crack edge vicinity

The discussion is based on the cell model of materials. Each cell contains one dominant kernel of micro-separation, for instance a particle. A cell is either in a cohesive or a decohesive state, the latter implying instability at load control. The process region consists of cells which have reached the decohesive state. The cells are characterized by their linear size and their cohesion-decohesion relation. The process region develops either in an elastic or in a plastic environment. In the latter case, it may be more or less deeply embedded in the plastic region. In some cases there will be no process region, only plastic flow. The ratio between the cohesive strength and the yield strength is an important parameter for describing this competition between decohesion and plastic flow, but the T-stress also plays a part. The fracture toughness depends on the area under the cohesion-decohesion curve and on the embedment of the process region.     

Effect of friction stir welding process parameters on the tensile strength of dissimilar aluminum alloy AA2024-T3 and AA7075-T6 joints

This work investigates the influence of friction stir welding parameters on the mechanical properties of the dissimilar joint between AA2024-T3 and AA7075-T6. Experiments are conducted consistent with the three-level face-centered composite design. Response surface methodology is used to develop the regression model for predicting the tensile strength of the joints. The analysis of variance technique is used to access the adequacy of the developed model. The model is used to study the effect of key operating process parameters namely, tool rotation speed, welding speed and shoulder diameter on the tensile strength of the joints. The results indicate that friction stir welding of aluminum alloys at a tool rotation speed of 1050 min⁻¹, welding speed of 40 mm/min and a shoulder diameter of 17.5 mm would produce defect less joint with high tensile strength.     

Mathematical model of critical implant stress testing in the weld metal of API 5L X80 steel

In this paper the influence of heat input and preheat temperature on the critical implant stress was analyzed for the weld metal of API 5L X80. High strength steel marked as API 5L X80 is produced with a thermo – mechanical controlled process (TMCP), its chemical composition shows low carbon content due to which the steel has good weldability, but in the weld metal zone cold cracking can occure. The goal of this paper is to define optimal work conditions in form of flux cored arc welding (FCAW) welding parameters at which no cold cracks can be found. The experiment was conducted using central composite design (CCD) and design of experiments (DoE) with two independent variables (preheat temperature and heat input). Mathematical models were developed for all three different wire types that were used (two rutile, one basic flux cored wire). The samples in this paper which had cold cracks were further analyzed on the scanning electron microscope (SEM).     

Effect of surface stress and irregularity of the interface on the propagation of SH-waves in the magneto-elastic crustal layer based on a solid semi space

The object of the present paper is to investigate plane SH waves through a magneto-elastic crustal layer based over an elastic, solid semi space under the influence of surface stress on the free surface of the crustal layer and irregularity of the interface. Two types of irregularities of the interface namely, rectangular and parabolic have been considered. Modulations of wave velocity due to the presence of surface stress, irregularity and the magnetic field have been studied separately. Their combined effect has also been investigated. Graphs are drawn to highlight some important peculiarities. It is observed that surface stress, irregularity and magnetic field have their respective role to play in the propagation of SH waves in the crustal layer. Further modulation of wave velocity occurs due to their combined effect.     

结构风工程研究的现状和展望

结构风工程问题研究是风工程学科形成的起源。经过半个世纪的发展，已经奠定了结构风工程的理论基础，可以满足一般结构的抗风设计要求。２１世纪结构长大化、高耸化以及外形复杂化的趋势使结构风工程研究面临新的挑战，需要对现行的理论和方法进行精细化的改进和发展，同时开展有效风振控制方法的研究，为解决大型复杂结构的风工程问题作好准备。