Release Rate Equation Research Articles

A continuum damage model for fatigue life prediction of 2.5D woven composites

Abstract A new model based on continuum damage mechanics is proposed to predict the fatigue life of 2.5D woven composites. First, a full-cell model reflecting the real microstructure of 2.5D woven composites is established in ANSYS. Subsequently, three independent damage variables are defined in the framework of the composite micromechanics to establish the component constitutive relations associated with damage. The strain energy density release rate and damage evolution equations for the matrix, fiber in yarns, and matrix in yarns are derived. Finally, the proposed model is implemented for fatigue life prediction and damage evolution analysis of 2.5D woven composites at 20 and 180°C. The results show that the numerical results are in good agreement with the relevant experimental results.

Distribution of Vital, Environmental Components and Nutrients Migration Over Sedimentary Water Layers

Contaminated marine sediment is a secondary pollution source in the coastal areas, which can result in increased nutrients concentrations in the overlying water. We analyzed the nutrients release characteristics into overlying water from sediments and the interaction among benthic circulation of nitrogen, phosphorus, iron, and sulfur were investigated in a preset sediment/water column. Profiles of pH, ORP, sulfur, iron, nitrogen, phosphorus pools were determined in the sediment and three different layers of overlying water. Variety types of sulfur in the sediments plays a significant role on nutrients transfer into overlying water. Dissimilatory nitrate reduction and various sulfur species interaction are predominantly embodied by the enhancing effects of sulfide on nitrogen reduction. Contaminant sediment take on high organic matter, which is decomposed by bacteria, as a result promote bacterial sulfate reduction and generate sulfide in the sediment. The sulfur and iron interactions had also influence on phosphorus cycling and released from sediment into overlying water may ensue over the dissolution of ferric iron intercede by iron-reducing bacteria. The nutrients release rate was calculated followed by release rate equation. The results showed that the sediments released large-scale quantity of ammonium nitrogen and phosphate, which are main inner source of overlying water pollution. A mechanical migration of key nutrients such as ammonia and inorganic phosphate was depicted numerically with Fick’s diffusion law, which showed a fair agreement to most of the experimental data.

폭발위험장소 설정 시 인화성액체 누출률의 최적 산정방법 연구

In order to determine the extent to which explosion-proof devices should be used in case of leakage in industrial sites handling flammable gases and flammable liquids, the calculation for classification of hazardous area should be carried out. At this time, the Korean Industrial Standard KS C 60079-10-1 citing IEC 60079-10-1, which is an international standard applied, is widely used. However, since the proposed liquid release rate equation does not clearly suggest a method of calculating the amount of vaporized, the calculation process is complicated, or excessive or insufficient results are induced. In order to improve this point, we propose an optimal liquid release rate calculation method, simplify the calculation process, and propose a practical and reasonable method.

Effect of stepwise humidity change on the release rate constant of 1-methylcyclopropene (1-MCP) in a cyclodextrin inclusion complex powder

The release behaviour of 1-methylcyclopropene (1-MCP) is important during postharvest treatment of fruit and vegetable. Effect of humidity and temperature on the release rate of 1-MCP in an α-cyclodextrin (α-CD) inclusion complex powder were investigated on the potential of direct application of 1-MCP inclusion complex powder and developing of functional packaging. The aim of this research was to study the release behaviour of 1-MCP from an inclusion complex powder under a stepwise humidity change. 1-MCP release experiments were conducted using a dynamic vapour sorption (DVS) system at different temperatures (40, 50, and 60 °C) with stepwise humidity changes (20% RH for 2 h to 40, 50, 60, and 80% RH for 2 h, respectively). The results showed that the release rate constant of 1-MCP from inclusion complex powders increased linearly with moisture concentration at 40, 50, and 60% RH. The highest release rate constant of 1-MCP was 1.5 × 10−3 s−1 for 80% RH at 60 °C. The activation energy at the highest humidity condition of 80% RH was 27.5 kJ/mol. The release rate constant of 1-MCP from the inclusion complex powders was well correlated with a first-order release rate equation. The results obtained showed that 1-MCP inclusion complex in α-CD has a potential as an active compound that could be incorporated into active packaging systems where storage condition below 60% RH is needed.

Experimental Investigation of the Size Effect of the Mode I Static Fracture Toughness of Limestone

To study the size effect of the fracture toughness of notched semicircular bend (NSCB) specimens, the dimensionless energy release rate equation of the NSCB specimen was deduced on the basis of the Bažant energy release rate. The influence of the crack length and the specimen size on the fracture toughness was analyzed. The Bažant scale equation was obtained using the International Union of Laboratories and Experts in Construction Materials, Systems, and Structures (RILEM) method. Finally, the Bažant equation was used to analyze the fracture toughness of an NSCB specimen with a radius of 75 mm, and the degree of variation was predicted. The results show that a longer fracture is correlated with a lower fracture toughness value for the same sample size and that a larger specimen radius is correlated with a higher fracture toughness value for the same crack length. The obtained Bažant equation correctly reflects the scale law of the fracture toughness of the NSCB specimen and provides highly accurate predictions of the fracture toughness of large specimens, with an error of not more than 3%. The results obtained in this study provide a new reference method and theoretical basis for the future testing work.

Release behavior of allyl sulfide from cyclodextrin inclusion complex of allyl sulfide under different storage conditions

The stability of allyl sulfide, an organosulfur compound present in garlic oil, in its α-, β-, and γ-cyclodextrin inclusion complexes was investigated under various storage conditions. The complexes of cyclodextrins and allyl sulfide were prepared by spray drying. The storage temperature, relative humidity, and initial moisture content of the inclusion complex had different effects on the release rate of allyl sulfide. Allyl sulfide in α-cyclodextrin complexes had a lower release rate than in β- and γ-cyclodextrin complexes at 100°C and at 50°C under 6, 40, 54, and 73% relative humidity. The initial moisture content affected only the release rate of allyl sulfide from α-cyclodextrin complexes. The release behavior of allyl sulfide can be correlated with the first-order release rate equation with a normal Gaussian distribution of free energy of activation of release rate constant. The results indicated α-cyclodextrin is a suitable material for controlled release of allyl sulfide.

A new approach for determining the R-curve in DCB tests without optical measurements

A new method for obtaining the R-curve point to point by the Double Cantilever Beam test is proposed. Besides the determination of new compliance and energy release rate equations, the analytical model presented leads to calculate the crack length for every pair of load and displacement values, without any optical measurement. In addition, a simple trigonometric approximation is proposed for the calculation of large displacement effects. The approach is checked with experimental results.

Stress control of plasma enhanced chemical vapor deposited silicon oxide film from tetraethoxysilane

Thin silicon dioxide films have been studied as a function of deposition parameters and annealing temperatures. Films were deposited by tetraethoxysilane (TEOS) dual-frequency plasma enhanced chemical vapor deposition with different time interval fractions of high-frequency and low-frequency plasma depositions. The samples were subsequently annealed up to 930 °C to investigate their stress behavior. Films that were deposited in high-frequency dominated plasma were found to have tensile residual stress after annealing at temperatures higher than 800 °C. The residual stress can be controlled to slightly tensile by changing the annealing temperature. High tensile stress was observed during the annealing of high-frequency plasma-deposited films, leading to film cracks that limit the film thickness, as predicted by the strain energy release rate equation. Thick films without cracks were obtained by iterating deposition and annealing to stack multiple layers. A series of wet cleaning experiments were conducted, and we discovered that water absorption in high-frequency plasma-deposited films causes the residual stress to decrease. A ∼40 nm thick low-frequency deposited oxide cap is sufficient to prevent water from diffusing through the film. Large-area free-standing tensile stressed oxide membranes without risk of buckling were successfully fabricated.

A new method for determining mode II R-curve by the End-Notched Flexure test

A new method for obtaining the mode II R-curve in a End-Notched Flexure test is proposed in the present work. New compliance and energy release rate equations have been derived incorporating shear, local deformation and bending rotation effects. Mode II R-curve, which represents energy release rate as a function of crack extension, is obtained without optical determination of crack tip position. Crack length and energy release rate are determined at each point of the test based on experimental compliance until unstable advance occurs. In order to confirm the theoretical models, unidirectional carbon/epoxy specimens have been tested. Experimental data are evaluated by means of two reduction schemes: an existing data method named Corrected Beam Theory with effective crack length and the new method named Beam Theory including Bending Rotation effects. Shear and local deformation effects are included in both reduction schemes. Results concerning the determination of crack length without crack advance and during stable crack propagation are presented. The agreement between experimental values and theoretical results obtained by the new approach is excellent. Based on the accurate crack length determination at each point of the test, energy release rate is determined point to point and therefore R-curve is obtained.

A guide to characterizing heat release rate measurement uncertainty for full‐scale fire tests

AbstractAccurate heat release rate measurements provide essential information to defining the fire safety characteristics of products. The size, complexity, and cost of full‐scale fire tests make achieving accurate and quantitative results a serious challenge. A detailed uncertainty analysis of a large‐scale heat release rate measurement facility is presented as a guide to the process of estimating the uncertainty of similar facilities. Quantitative heat release rate measurements of full‐scale fires up to 2.7 MW were conducted using the principle of oxygen consumption calorimetry. Uncertainty estimates were also computed for the heat input measurements from a well‐controlled natural gas burner. The measurements of heat input and heat release rate were performed independently, and the discrepancy between the two was well within the uncertainty limits. The propagation of uncertainty was performed at the level of voltage and temperature measurements, which avoided using mutually dependent measurement parameters. Reasons for the significant contribution to the combined uncertainty from the oxygen concentration and exhaust flow measurements are demonstrated. Also presented is a first‐order effort to account for the uncertainty due to factors in full‐scale fire tests such as operator error and environmental influences that are not modeled by the heat release rate equation. Published in 2008 by John Wiley & Sons, Ltd.

A modified 4-point bend delamination test

The 4-point bend delamination test is widely used to study the adhesive properties in thin film structures. The analysis of such tests is commonly based on assumption that symmetry conditions are appropriate to describe crack length and loading. These conditions are, however, rarely fulfilled, and it is common that only a single crack is being propagated. This fact is especially of concern in fatigue crack growth studies. Solutions for energy release rates for asymmetric 4-point bend delamination specimens are presented. A semi-articulated test fixture is described. The experiments conducted with this fixture and the additional energy release rate equations allow that cracks to both sides of the specimen are being propagated. In toughness testing this provides two values for the critical energy release rate from a single test. In fatigue testing, it is demonstrated that near symmetric crack growth was obtained, and remaining asymmetry effects can be quantified.

On the calculation of energy release rates for cracked laminates with residual stresses

Prior methods for calculating energy release rate in cracked laminates were extended to account for heterogeneous laminates and residual stresses. The method is to partition the crack tip stresses into local bending moments and normal forces. A general equation is then given for the total energy release rate in terms of the crack-tip moments and forces and the temperature difference experienced by the laminate. The analysis method is illustrated by several example test geometries. The examples were verified by comparison to numerical calculations. The residual stress term in the total energy release rate equation was found to be essentially exact in all example calculations.

Release Behavior of Flavor Encapsulated CD in Slurry Solution Under Boiling Conditions

Cyclodextrin (CD) can control flavor release rate and protect the flavor from volatilization by the formation of inclusion complex with flavor compounds. However, the flavor release rate during cooking, particularly in boiling water has hardly been understood. In this study, flavor release rate of flavor encapsulated CD in slurry or turbid solution under boiling condition was investigated. The release rate constants of methyl caproate and d-limonene depended on the CD concentration, whereas, those of phenyl ethanol hardly did. The plot of a reciprocal number of apparent release rate constant to CD concentration for d-limonene stability constant under boiling condition was obtained. Stability constants for d-limonene in α-CD and β-CD were 185 and 38 M−1, respectively. These stability constants were smaller than the order of 1000 M−1 at room temperature. These results suggested that the addition of CD for protection of flavors in boiling water might have small effect in comparison to that at room temperature. The behavior of flavor release in the boiling water correlated well with the first-order release rate equation, which can be described by the film theory of the interfacial mass transfer.

Mode-II Fracture in E-glass-polyester Composite

In this work a novel beam analysis of the end-loaded split (ELS) and over-notched flexure (ONF) specimens are presented. New compliance and strain energy release rate equations are developed incorporating crack tip deformation and transverse shear analysis. The Saint Venant effect at the clamped end of the ELS specimen is also considered. Unidirectional glass-polyester specimens are manufactured and experimental (initiation and propagation) tests are performed to confirm the theoretical models. The experimental data is evaluated by means of four reduction techniques: the exact beam theory, virtual crack closure technique, compliance calibration method, and direct beam theory. It is shown that the results by the four methods agree quite closely; however, the compliance calibration method is not recommended for initiation data reduction in the case of the ONF specimen. The ELS specimens suffer from relatively large displacements. Thus, propagation tests are not possible to be performed. The ONF test seems to be a better tool to evaluate the mode-II toughness of composite materials with low flexural modulus.

Fabrication of porous polymeric matrix drug delivery devices using the selective laser sintering technique.

New techniques in solid freeform fabrication (SFF) have prompted research into methods of manufacturing and controlling porosity. The strategy of this research is to integrate computer aided design (CAD) and the SFF technique of selective laser sintering (SLS) to fabricate porous polymeric matrix drug delivery devices (DDDs). This study focuses on the control of the porosity of a matrix by manipulating the SLS process parameters of laser beam power and scan speed. Methylene blue dye is used as a drug model to infiltrate the matrices via a degassing method; visual inspection of dye penetration into the matrices is carried out. Most notably, the laser power matrices show a two-stage penetration process. The matrices are sectioned along the XZ planes and viewed under scanning electron microscope (SEM). The morphologies of the samples reveal a general increase in channel widths as laser power decreases and scan speed increases. The fractional release profiles of the matrices are determined by allowing the dye to diffuse out in vitro within a controlled environment. The results show that laser power and scan speed matrices deliver the dye for 8-9 days and have an evenly distributed profile. Mercury porosimetry is used to analyse the porosity of the matrices. Laser power matrices show a linear relationship between porosity and variation in parameter values. However, the same relationship for scan speed matrices turns out to be rather inconsistent. Relationships between the SLS parameters and the experimental results are developed using the fractional release rate equation for the infinite slab porous matrix DDD as a basis for correlation.

SANDWICH STRUCTURE DELAMINATION OF RESIN TRANSFER MOLDING

One of the apparent advantages of sandwich structures is that after the core is made, the sandwich is produced in one process by resin transfer molding (RTM) and no adhesive is used between the core and skins. The bond between the core and skins is therefore likely to depend upon the core material, the type of matrix and the core surface roughness. This is of great importance, because the stiffness of the sandwich structure is likely to be reduced by even partial delamination of the core and skins. The objective of this study was to ascertain the effects of manufacturing parameters such as injection pressure, mold temperature, core thickness and core surface roughness on skin/core adhesion using the direct tensile adhesion and peel test methods. Polyurethane foam was used as the core material throughout the work. The major objective was to examine different surface treatment methods by which the strength of the skin–core bond could be improved. The influence of the core surface roughness on the adhesive fracture energy and the delamination between core and skin were also measured. The fracture energy release rate equation was used as the basis for comparison and for measurements of the adhesion. For this purpose a double-cantilever beam was used to characterize the delamination. Critical energy release rate (G IC) and fracture toughness (K IC) were calculated using several alternative methods based on linear elastic fracture mechanics.

Modelling of photoinduced discharge of photoreceptors under pulsed photoexcitation: small and large signal xerographic time-of-flight analysis

A general theoretical model for the photoinduced discharge of a charged photoreceptor is developed by considering non-dispersive charge transport in a high-resistivity semiconductor (insulator in the dark), point form representations of Ohm's law, Gauss's law and Maxwell's equations for the total current, and the trapping and release rate equations. The rate equations incorporate arbitrary strengths of trapping, release, and trap saturation for a single level of traps. In contrast to most previous works, the trap filling effect is fully incorporated into the model which allows its effects to be studied. These equations were combined to create a single general second-order nonlinear partial differential equation which governs the behaviour of the electric field during photoinduced discharge. The general differential equation for the field was then solved numerically using boundary conditions that are representative of pulsed illumination. Solutions were obtained under low injection (0.1% of surface charge) and high injection (10%, 50%, and 99% of surface charge) conditions. Trapping parameters in the model could be adjusted to represent a wide range of trapping conditions including trap saturation. In each case, the time evolution of the discharge was monitored by calculating the trapped and untrapped charge densities at regular intervals throughout the discharge. By differentiating the calculated surface voltage V, the rate discharge dV/dt was also monitored, because it is an experimentally accessible quantity that is widely used in xerographic time-of flight measurements. Results obtained under low injection conditions demonstrated that the dispersion in the charge packet increased with larger values of the mobility reduction factor and smaller values of the trapping and release rates, and r, respectively. Increased charge packet dispersion was seen to cause increased dispersion in dV/dt near the transit time. The temporal spread of arrival times analytically predicted by the Schmidlin equation was found to be in good agreement with the present model in the small signal mode. High injection results illustrated that the dispersion of the charge packet and |dV/dt| increased dramatically with increased injection strength. Under extremely high injection, the dispersion is primarily determined by the amount of injection. The effect of trap saturation under high injection conditions was also investigated. Increased trap saturation caused the packet to become more spread out during the early stages of the discharge. This caused significant decay in |dV/dt| before the shallow-trap controlled transit time, but did not significantly affect the overall dispersion in |dV/dt|.

346 アクチュエータを用いた積層複合材料のはく離進展抑制効果

In the present paper, delamination suppression by induced strain actuators bonded to FRP laminates was examined. For two dimensional delamination cracks, the reduction in the strain energy release rates due to actuation strains was analysed by the simple beam method. The beam theory solutions were compared with the results of the boundary element analysis. Change in apparent crack growth resistance with actuation strains was estimated from the energy release rate equation based on the beam theory. When compared at the same actuation strain, the suppression effect for mode I cracks was large than that for mode II cracks.

Evaluation of heat release rate equations used in standard test methods

A thorough review was recently conducted to verify the correctness of equations being used to calculate heat release rate in standard test methods. The review incorporated 17 different standard test methods from American Society of Testing and Materials (ASTM), National Fire Protection Association (NFPA), Uniform Building Code (UBC), California Technical Bulletin (CA TB), International Standards Organization (ISO), and British Standards (BS). The standard test methods reviewed were ASTM D5424, ASTM D5537, ASTM E1354, ASTM E1537, ASTM E1590, ASTM E1623, ASTM E1822, NFPA 264, NFPA 265, NFPA 266, NFPA 267, CA TB 129, CA TB 133, UBC 8-2, UBC 26-8, ISO 5660, BS 476. Through this review, incorrect equations were found in 12 of the 17 standards with a total of 22 incorrect equations overall. The following paper provides the correct heat release rate equations and a summary of the review. © 1998 John Wiley & Sons, Ltd.

Sodium Fire Code SFIRE1C for Pool Fire Characteristics

Sodium pool fire code, SOFIRE II, written for the constant value of stoichiometric combustion ratio and heat of reaction is used to compute the buildup of pressure and temperature in a containment. In the SOFIRE II model, for the formation of a mixture of Na2O and Na2O2 in the sodium pool, the input stoichiometric combustion ratio and heat of formation values need to be varied to corresponding values admissible for the mixture. In the present work, the SOFIRE II one-cell model is revised and the present version SFIRE1C (Sodium FIRE 1 Cell model) accounts for the formation of Na2O in an early stage of the fire and shifts to the formation of Na2O2 at a later stage. Thus SFIRE1C computes in a more realistic manner the reaction products which are formed in the pool. The model for sodium oxide aerosol release is also modified in this version, by incorporating a more appropriate aerosol release rate equation. The calculated values using the SFIRE1C one-cell model are compared with sodium pool fire experimental results.