Long-duration Tests Research Articles

Groundwater Characteristics’ Assessment for Productivity Planning in Al-Madinah Al-Munawarah Province, KSA

In recent times, drilling groundwater wells for irrigation, domestic, and industrial uses is increasing at a high rate in Saudi Arabia, meaning that groundwater is becoming a primary water resource. In the study region, over-exploitation and unsustainable performance severely deteriorate groundwater. Therefore, it is important to monitor the groundwater levels and quality as well as to detect the hydraulic parameters in order to plan and maintain groundwater sustainability. Knowledge of aquifer hydraulic parameters and groundwater quality is essential for the productivity planning of an aquifer. Therefore, this study carried out a thorough analysis on measured depth to groundwater data (2017 and 2022), borehole pumping test records, and chemical analysis of the collected water samples, especially in the presence of overexploitation and scarcity of recharge scale. To accomplish this aim, measurements of 113 groundwater wells (including 103 water samples) and analysis of 29 pumping tests between step and long-duration tests were made of all aquifer characteristics. These parameters consist of well loss, formation loss, well efficiency, specific capacity, transmissivity, hydraulic conductivity, resulted drawdown, and physiochemical parameters. Thematic maps were generated for all parameters using the geographic information system (GIS) and diagrams to strategize the groundwater productivity in Al-Madinah Al-Munawarah Province. The estimated hydraulic parameters are highly variable. Four distinct portions were identified for aquifer potentiality based on these varying ranges. Both the north and east of the region are good for groundwater productivity due to good aquifer materials, whereas the southwestern and western portions have relatively poor values. The analyzed groundwater was categorized as fresh to slightly salty water, with two primary chemical types identified showing a prevalence of mixed NaCl and Ca-Mg-SO4/Cl water. Finally, groundwater productivity assessment predicts that the aquifers can support the Al-Madinah Al-Munawarah Province demand for several years if certain well distributions are adopted and for a few hours/day of pumping rate. The maps that have been created can be examined to aid in making decisions related to hydrology.

Quantification and prediction of error in MIMO tests

Dynamic testing of systems is most realistic of real-world conditions when multiple input and multiple output (MIMO) techniques are used. To replicate measured environmental conditions, a series of desired outputs (responses) on the system must be realized by inverting the frequency response functions (FRF) matrix for input estimation. System identification is dependent on the number of inputs and outputs, which affect the type of solutions. In input estimation, the auto spectra of the determined inputs are affected by both the auto spectra and cross spectra of the desired outputs. This research evaluates errors and investigates two sources in an experimental setting. The first significant error source is test-to-test variability in FRFs from system identification tests, quantified by magnitude variability from long-duration tests. The second significant error source is the realization of time histories from frequency domain inputs. The spectral content of the realized random process deviates from the desired content and is also quantified. The structure is a linear three-story frame fixed at the base; two inputs are provided uniaxially with the use of suspended electrodynamic shakers. The proposed model for error sources was found to be effective in predicting errors in a SISO (single-input single-output) and a square (2-input 2-output) MIMO test.

Development of Long Duration Button Cell Test Stands and Testing Protocols

Increasing the longevity of SOEC systems is a key impact for hydrogen production. Improving stack lifetime from 20,000 to 60,0000 hours results in a cost reduction of $.20 on the levelized cost of hydrogen. Long duration test stand development for button cells is a growing need to establish Accelerated Stress Testing, and long-duration testing benchmarks. Improving the reliability of test stands and long-term cell testing enables deeper investigations into long-term degradation behavior. Significant deviations between cell degradation mechanisms during the initial 500 hours of operation and the mechanisms after 500 hours exist. Establishing the mechanisms of long-duration degradation as opposed to initial break-in stability is necessary in order to achieve reliable systems that can operate for upwards of 80,000 hours.

Efficient, Breathable, and Compostable Multilayer Air Filter Material Prepared from Plant-Derived Biopolymers.

State-of-art face masks and respirators are fabricated as single-use devices using microfibrous polypropylene fabrics, which are challenging to be collected and recycled at a community scale. Compostable face masks and respirators can offer a viable alternative to reducing their environmental impact. In this work, we have developed a compostable air filter produced by electrospinning a plant-derived protein, zein, on a craft paper-based substrate. The electrospun material is tailored to be humidity tolerant and mechanically durable by crosslinking zein with citric acid. The electrospun material demonstrated a high particle filtration efficiency (PFE) of 91.15% and a high pressure drop (PD) of 191.2 Pa using an aerosol particle diameter of 75 ± 2 nm at a face velocity of 10 cm/s. We deployed a pleated structure to reduce the PD or improve the breathability of the electrospun material without compromising the PFE over short- and long-duration tests. Over a 1 h salt loading test, the PD of a single-layer pleated filter increased from 28.9 to 39.1 Pa, while that of the flat sample increased from 169.3 to 327 Pa. The stacking of pleated layers enhanced the PFE while retaining a low PD; a two-layer stack with a pleat width of 5 mm offers a PFE of 95.4 ± 0.34% and a low PD of 75.2 ± 6.1 Pa.

Damage Evolution Prediction during 2D Scale-Model Tests of a Rubble-Mound Breakwater: A Case Study of Ericeira’s Breakwater

Melby presents a formula to predict damage evolution in rubble-mound breakwaters whose armour layer is made of rock, based on the erosion measured in scale-model tests and the characteristics of the incident sea waves in such tests. However, this formula is only valid for armour layers made of rock and for the range of tested sea states. The present work aims to show how the Melby methodology can be used to establish a similar formula for the armour layer damage evolution in a rubble-mound breakwater where tetrapods are employed. For that, a long-duration test series is conducted with a 1:50 scale model of the quay section of the Ericeira Harbour breakwater. The eroded volume of the armour layer was measured using a Kinect position sensor. The damage parameter values measured in the experiments are lower than those predicted by the formulation for rock armour layers. New ap and b coefficients for the Melby formula for the tested armour layer were established based on the minimum root mean square error between the measured and the predicted damage. This work shows also that it is possible to assess the damage evolution in scale-model tests with rubble-mound breakwaters by computing the eroded volume and subsequently, the dimensionless damage parameter based on the equivalent removed armour units.

Vision-based damage analysis in shoe-braking tests on railway wheel steels

Small-scale experimental tests were carried out by a bi-disc machine to reproduce the phenomena occurring in shoe-braked railway wheels. Wheel specimens of three different steels were subjected first to a braking step against cast iron brake-block specimens in full sliding condition, then to a running step against a rail steel in rolling-sliding condition. To monitor the damage occurring at the wheel specimen surface, a vision system, based on a high-speed camera acquiring the surface images during the tests, was implemented. An image analysis procedure was elaborated to evaluate the surface state by means of quantitative synthetic indexes. The correlation of such indexes with the damage was validated by means of comparison with the subsurface state, obtained by optical microscope observation of cut specimens. Finally, the synthetic indexes were used to analyse the evolution of the damage on a long-duration test, proving to be effective as a non-destructive damage monitoring tool.

Effects of groundwater flow on thermal response test of deep borehole heat exchanger

Deep borehole heat exchanger (DBHE) has a great potential to exploit geothermal energy, and although many studies are conducted on DBHE, the effects of groundwater flow on thermal response test (TRT) results of DBHE remain to be uncovered. This paper utilizes a numerical model to simulate TRT of a DBHE with groundwater flow, and the simulated TRT data are used for estimation of effective ground thermal properties based on a parameter estimation method and a semi-analytical heat transfer model, and then the effects of groundwater flow on the TRT results of DBHE are investigated under different conditions. When Darcy velocity is high enough, groundwater flow would lead to overestimation of effective ground thermal conductivity and underestimation of effective volumetric heat capacity of ground, and the effective ground thermal properties have larger error for higher Darcy velocity and longer test duration, and using the effective ground thermal properties would underestimate the long-term DBHE performance. The effect of groundwater flow on the TRT results of DBHE is greater for lower ground thermal conductivity and lower volumetric heat capacity of ground, and is slightly influenced by other parameters. The results of this paper offer some guidelines for TRT of DBHE with groundwater flow.

Experimental Research of Two-phase Rotating Detonation Combustor Operating with High Total Temperature Air

Experiments on a two-phase rotating detonation combustor operating with gasoline and high total temperature air were conducted to investigate the initiation characteristics, operation mode, and propagation characteristics of a two-phase rotating detonation wave (RDW). The outer diameter, inner diameter, and length of the annular combustor were 204 mm, 166 mm, and 155 mm, respectively. The initiation characteristics, operation mode, and propagation characteristics of the two-phase RDW were studied by varying the total air temperature. The experimental results show that the initiation time of the RDW first decreases and then increases with an increase in the total air temperature and reaches an extreme value at a total air temperature of 713 K. Four operation modes (failure, intermittent detonation, single wave, coexistence of double wave collision, and single wave) of the detonation combustor were found for different total air temperatures. The effect of the total air temperature on the peak pressure stability and propagation frequency of the RDW was studied in detail. From the results, the effect of the equivalence ratio on the working characteristics of a rotating detonation engine (RDE) was investigated at a total air temperature of 713 K. Four detonation propagation modes (sporadic detonation, intermittent detonation, single-wave mode, coexistence of double-wave collision and single wave) were obtained in the combustor. When the equivalence ratio was 0.52, the detonation initiation failed. The pressure characteristics in the combustor and propagation frequency of the RDW were studied with different equivalence ratios. In addition, a long-duration test was performed for 3 s to verify the continuous working feasibility of the two-phase RDE.

Does Kinematic Alignment Increase Polyethylene Wear Compared With Mechanically Aligned Components? A Wear Simulation Study.

Kinematic alignment is an alternative approach to mechanical alignment. Kinematic alignment can restore the joint line to its prearthritic condition, and its advocates have suggested it may be associated with other benefits. But this alignment approach often results in tibial components that are placed in varus and femoral components that are placed in valgus alignment, which may result in an increased risk of component loosening because of wear. Like malaligned implant components, kinematically aligned knee implants could increase wear in vivo, but we lack comparative data about wear behavior between these approaches. (1) Do the different alignment approaches (kinematic, mechanical, and purposefully malaligned components) result in different wear rates in a wear simulator? (2) Do the different alignment approaches lead to different worn areas on the polyethylene inserts in a wear simulator? (3) Do the different alignment approaches result in different joint kinematics in a wear simulator? Mechanical alignment was simulated in a force-controlled manner with a virtual ligament structure according to the International Organization for Standardization (ISO 14243-1) using a knee wear simulator. To simulate kinematic alignment, flexion-extension motion, internal-external torque, and the joint line were tilted by 4°, using a novel mechanical setup, without changing the force axis. The setup includes bearings with inclinations of 4° so that the joint axis of 4° is determined. To verify the angle of 4°, a digital spirit level was used. To simulate malalignment, we tilted the implant and, therefore, the joint axis by 4° using a wedge with an angle of 4° without tilting the torque axes of the simulator. This leads to a purposefully malaligned tibial varus and femoral valgus of 4°. For each condition, three cruciate-retaining knee implants were tested for 3.0 x 10 6 cycles, and one additional implant was used as soak control. Gravimetric wear analyses were performed every 0.5 x 10 6 cycles to determine the linear wear rate of each group by linear regression. The wear area was measured after 3.0 x 10 6 cycles by outlining the worn areas on the polyethylene inserts, then photographing the inserts and determining the worn areas using imaging software. The joint kinematics (AP translation and internal-external rotation) were recorded by the knee simulator software and analyzed during each of the six simulation intervals. Comparing the wear rates of the different groups, no difference could be found between the mechanical alignment and the kinematic alignment (3.8 ± 0.5 mg/million cycles versus 4.1 ± 0.2 mg/million cycles; p > 0.99). However, there was a lower wear rate in the malaligned group (2.7 ± 0.2 mg/million cycles) than in the other two groups (p < 0.01). When comparing the total wear areas of the polyethylene inserts among the three different alignment groups, the lowest worn area could be found for the malaligned group (716 ± 19 mm 2 ; p ≤ 0.003), but there was no difference between kinematic alignment and mechanical alignment (823 ± 19 mm 2 versus 825 ± 26 mm 2 ; p > 0.99). Comparing the AP translation, no difference was found between the mechanical alignment, the kinematic alignment, and the malalignment group (6.6 ± 0.1 mm versus 6.9 ± 0.2 mm versus 6.8 ± 0.3 mm; p = 0.06). In addition, the internal-external rotation between mechanical alignment, kinematic alignment, and malalignment also revealed no difference (9.9° ± 0.4° versus 10.2° ± 0.1° versus 10.1° ± 0.6°; p = 0.44). In the current wear simulation study, the wear rates of mechanical alignment and kinematic alignment of 4° were in a comparable range. The results suggest that kinematic alignment with up to 4° of component inclination may give the surgeon confidence that the reconstruction will have good wear-related performance when using a modern cruciate-retaining implant. The malaligned group had the lowest wear rate, which may be a function of the smaller worn area on the inserts compared with the other two alignment groups. This smaller articulation area between the femoral condyles and polyethylene insert could increase the risk of delamination of malaligned components over longer test durations and during high-load activities. For that reason, and because malalignment can cause nonwear-related revisions, malalignment should be avoided. Further in vitro and clinical studies must prove whether the wear simulation of different alignments can predict the wear behavior in vivo.

Inflated Cone Experiment for High-Throughput Characterization of Time-Dependent Polymer Membranes

Abstract Long-term behavior of polymer membranes in the nonlinear regime is probed by strain histories under various stress levels. Current characterization methods for polymer membranes impose a uniform stress field and hence require a series of long-duration tests to be conducted, which poses a significant experimental challenge. Here, we present the inflated cone method to generate a continuous spectrum of strain histories under various stresses in a single experiment. By imposing a known stress gradient and utilizing a full-field strain measurement technique, the inflated cone method provides a high-throughput approach for extracting time-dependent data of polymer membranes. The method is suitable for studying nonlinear time-dependent deformations under a biaxial stress state. The stress range and ratio can be easily modulated by cone geometry design. We demonstrate the utility of the method through creep-recovery tests carried out on a polyethylene thin film. The proposed experimental method is highly beneficial for the development of nonlinear viscoelastic and viscoplastic models.

Performance of Statistical Indicators in the Objective Detection of Speech-Evoked Envelope Following Responses.

To assess the sensitivity of statistical indicators used for the objective detection of speech-evoked envelope following responses (EFRs) in infants and adults. Twenty-three adults and 21 infants with normal hearing participated in this study. A modified/susa∫i/speech token was presented at 65 dB SPL monoaurally. Presentation level in infants was corrected using in-ear measurements. EFRs were recorded between high forehead and ipsilateral mastoid. Statistical post-processing was completed using F -test, Magnitude-Square Coherence, Rayleigh test, Rayleigh-Moore test, and Hotelling's T 2 test. Logistic regression models assessed the sensitivity of each statistical indicator in both infants and adults as a function of testing duration. The Rayleigh-Moore and Rayleigh tests were the most sensitive statistical indicators for speech-evoked EFR detection in infants. Comparatively, Magnitude-Square Coherence and Hotelling's T 2 also provide clinical benefit for infants in all conditions after ~30 minutes of testing, whereas the F -test failed to detect responses to EFRs elicited by vowels with accuracy greater than chance. In contrast, the F-test was the most sensitive for vowel-elicited response detection for adults in short tests (<10 minute) and performed comparatively with the Rayleigh-Moore and Rayleigh test during longer test durations. Decreased sensitivity was observed in infants relative to adults across all testing durations and statistical indicators, but the effects were largest in low frequency stimuli and seemed to be mostly, but not wholly, caused by differences in response amplitude. The choice of statistical indicator significantly impacts the sensitivity of speech-evoked EFR detection. In both groups and for all stimuli, the Rayleigh test and Rayleigh-Moore tests have high sensitivity. Differences in EFR detection are present between infants and adults regardless of statistical indicator; however, these effects are largest for low-frequency EFR stimuli and for amplitude-based statistical indicators.

Step-drawdown tests: linear and nonlinear head loss components

Coefficients B and C of the Jacob (1947) equation, usually derived from step-drawdown tests, are commonly attributed to “aquifer losses” and “well losses”, respectively. This paper analyzes and separates the linear laminar, nonlinear laminar and turbulent losses occurring during flow from an aquifer to a screened well. From this, one can derive a detailed physical meaning for both coefficients. The coefficient B does not contain only aquifer losses but also linear losses from the gravel pack and wellbore skin, if present. Coefficient C contains nonlinear laminar losses from the gravel pack and turbulent losses caused by screen inflow and vertical flow through the screen and casing. In some cases, the turbulent losses are small enough to be omitted. For transient flow at larger times, the changes in linear laminar losses within the aquifer become important. A new, explicit formulation of the Jacob equation was compared to long-duration field step-drawdown tests, three in confined unconsolidated formations and one in a fractured rock aquifer. Jacob C.E. (1947) Drawdown test to determine effective radius of artesian wells. Trans. Am. Soc. Civil Eng. 112:1047–1070.

Permeability and solute sorption of unamended and polymer-enhanced geosynthetic clay liners

Polymer treatment is an increasingly adopted approach to mitigate the impact of aggressive liquids on the hydraulic performance of geosynthetic clay liners (GCLs). Dense prehydrated (DPH) GCLs are particular products that combine polymer treatment, prehydration and densification to improve the overall containment performance. This study investigated the saturated hydraulic conductivity, k, and heavy-metal retention in a conventional GCL and a DPH GCL. Both materials were permeated first with water and then with a synthetic solution containing zinc (Zn), copper (Cu) and lead (Pb), also with the purpose of extending a previous study where a solution of the same solutes at higher concentrations had been used. The k of the conventional GCL increased by one order of magnitude with respect to that of water upon permeation with the synthetic solution. The solutes were partly retained, and the increase in k was associated with the breakthrough of solutes. Upon permeation with the same solution, the k of the DPH GCL decreased by a factor of 1.6 with respect to that of water. No significant breakthrough of metals was observed, despite the considerably longer test duration. Under the adopted testing conditions, owing to polymer amendment and densification, the hydraulic performance and solute retention properties of the DPH GCLs were superior to those of the conventional GCL.

Effect of high-pressure detonation products on fuel injection and propagation characteristics of detonation wave

The effect of high-pressure detonation products on fuel injection and propagation characteristics of detonation wave has been investigated in the form of ion voltage by varying the equivalence ratio (ER), air mass flux, and operation duration with hydrogen-air mixtures. It has been shown experimentally that the ion voltage decays gradually during the initial stage of rotating detonation wave (RDW). The attenuation of ion voltage is a general phenomenon, and the decay rate of ion voltage and its peak value of the trough state are related to the equivalence ratio and air mass flux. The analysis of interaction between the combustor and hydrogen plenum indicates that the feedback of high-pressure detonation products leads to the attenuation of ion voltage. In addition, the long-duration tests show that the ion voltage will recover to a steady state with the extension of reaction time, when the purgation (products leaving plenums) of detonation products is greater than feedback (products entering plenums) of detonation products in the hydrogen plenum. The recovery of ion voltage starts earlier at the higher equivalence ratio and air mass flux, and the peak value of ion voltage in the steady state also increases with the increase of equivalence ratio and air mass flux. A low frequency oscillation about 10–12 Hz occurs in the RDW at some operation conditions. This low frequency oscillation is related to the interaction between the combustor and hydrogen plenum, and can be eliminated by either increasing the equivalence ratio or decreasing the air mass flux.

Dry wear response of a Zn-based alloy containing 37.5% Al as affected by sliding conditions

Abstract This paper discusses the observations made pertaining to dry sliding wear characteristics of a Zn-based alloy at different sliding speeds and pressures. The wear rate increased with speed and pressure. The wear rate versus pressure plots attained two slopes wherein the slope was low up to a specific pressure followed by an increased slope at still higher pressures. This trend was observed at all the sliding speeds except the maximum; in the latter case one slope (identical to that of the higher slope at the lower speeds) only was noted. The seizure pressure was noted to decrease with speed. The temperature near the specimen surface increased with test duration, pressure and sliding speed. The rate of temperature increase was significantly high initially. This was followed by a lower rate of increase in temperature at longer test durations. In some cases, the rate of temperature increase became high once again towards the end of the tests. The influence of applied pressure and sliding speed on the temperature increase was practically identical to that on wear rate. Lower wear rate of the alloy agreed with less surface/subsurface damage and finer debris formation and vice versa.

Pad test for urinary incontinence diagnosis in adults: Systematic review of diagnostic test accuracy.

The pad test is an assessment tool for urinary incontinence (UI) severity classification and therapeutic response monitoring. However, the reliability and reproducibility of this test have been questioned. To summarize the evidence regarding the accuracy measures and reproducibility of different pad test protocols for assessing UI. A systematic review of the diagnostic accuracy of this tool was performed (CRD42020219392). Studies reporting data on the accuracy measures and reproducibility of the pad test when used for detecting UI in adult men and women. MEDLINE, Science Direct, Cochrane, Web of Science, LILACS, and Pedro. Two reviewers independently screened the articles, extracted the data, and evaluated the risk of bias (RoB) using the QUADAS-2 tool. From 1048 studies, 18 studies were included. Eight of these reported accuracy data, and 12 reported reproducibility properties. A total of 1070 individuals were analyzed, whose mean age ranged from 20 to 90 years. The accuracy of the long-duration protocols was generally moderate to high (sensitivity, 60%-93%; specificity, 60%-84%). The 1-hprotocols obtained higher accuracy values. The overall reproducibility was moderate to high (κ ≥ 0.66). The RoB was high and, due to different cutoff points adopted by studies, the bivariate model was not satisfied to perform a meta-analysis. The 1-hpad test was more accurate but less reproducible when compared to the long-duration tests. Pad test results should be used with caution in clinical practice.

Assessing a commercial steam methane reforming catalyst for tar removal in biomass gasification

This study assessed performance of a steam methane reforming (SMR) catalyst for reforming tar produced during biomass gasification. Bench–scale reforming tests are presented using methanol/water mixtures with guaiacol or toluene in the range of 0–4 wt%. Long-duration tests indicate that the SMR catalyst could operate for thousands of hours at 0.5 wt% tar loading. Tests at tar loadings up to 4 wt% showed deactivation rate was directly proportional to tar loading and, at 4 wt% loading, resulted in reduced performance during 24 h on stream. Overall, the SMR catalyst exhibited excellent characteristics for application in a step–wise catalytic tar reforming process. The SMR catalyst had higher activity for methanation than a commercial automotive catalyst previously assessed for tar reforming, which could be advantageous for commercial RNG production. The COCO process simulator was used to model and compare the experimental results of bench-scale tests.

An Ultra-Fast TSP on a CNT Heating Layer for Unsteady Temperature and Heat Flux Measurements in Subsonic Flows.

In this paper, the authors demonstrate the application of a modified Ru(phen)-based temperature-sensitive paint which was originally developed for the evaluation of unsteady aero-thermodynamic phenomena in high Mach number but short duration experiments. In the present work, the modified TSP with a temperature sensitivity of up to −5.6%/K was applied in a low Mach number long-duration test case in a low-pressure environment. For the demonstration of the paint’s performance, a flat plate with a mounted cylinder was set up in the High-Speed Cascade Wind Tunnel (HGK). The test case was designed to generate vortex shedding frequencies up to 4300 Hz which were sampled using a high-speed camera at 40 kHz frame rate to resolve unsteady surface temperature fields for potential heat-transfer estimations. The experiments were carried out at reduced ambient pressure of = 13.8 kPa for three inflow Mach numbers being . In order to enable the resolution of very low temperature fluctuations down to the noise floor of K with high spatial and temporal resolution, the flat plate model was equipped with a sprayable carbon nanotube (CNT) heating layer. This constellation, together with the thermal sensors incorporated in the model, allowed for the calculation of a quasi-heat-transfer coefficient from the surface temperature fields. Besides the results of the experiments, the paper highlights the properties of the modified TSP as well as the methodology.

Application of activated carbon fabric for the removal of a recalcitrant pesticide from agricultural run-off

Removal of pesticides from agricultural run-off close to the point of application has the potential to prevent or reduce the pollution of water sources used for drinking. This research considered the novel application of activated carbon (AC) fabric as a sorbent material for removal of pesticides from field run-off. AC fabric was tested for the removal of the molluscicide pesticide metaldehyde under a range of flow rates at both laboratory and pilot scale. Metaldehyde at an initial concentration of 10 μg/L was removed effectively from deionised (DI) water and real source water by the AC cloth under all conditions tested, reaching removal of 1375 and 876 μg/g (equivalent to 169 and 264 mg/m2), respectively. The adsorption followed pseudo-second order kinetics (k2 of 29.9 and 34.8 g/μg min for the AC fabric and GAC), providing rapid removal of metaldehyde within the first 5 min of contact. In single pass and flow through conditions, stabilised removal of 46% metaldehyde was achieved by the AC fabric bundle for treatment of 700 L of real water in a pilot scale flume. This equated to removal of 454 μg/m2, although significantly more removal would be expected over longer duration testing given the stabilised removal and the equilibrium capacity of the fabric seen during the batch isotherm testing. The work provides evidence to show that AC fabric could be used in the catchment to reduce peak loads of pesticides in sources used for drinking water.

Finite Element Modelling of Creep Rupture on Grade 91 Steel using Monkman-Grant Ductility based Damage Model

Failure strain is a main parameter used in the ductility exhaustion based damage model in which the accuracy of the prediction is dependent on its input value. The experimental measured has indicated that the value of strain at fracture is extensively scattered, therefore may affect the prediction. This paper presents the result of creep rupture time using a modified creep damage model incorporating Monkman-Grant (MG) failure strain as an alternative to strain at fracture. Both strains at fracture and MG failure strain are separately employed in the damage model to predict the failure time of uniaxial smooth specimen and notched bar with different acuity ratios of 3.0 and 20. The FE model of the specimen is loaded under different stress values and the multiaxial failure strain at each stress level is estimated using Cock and Ashby void growth model. The predicted creep rupture time that is compared to the experimental data (in a range of 40-1000 hours) showing a good agreement within the scatter band of +/-factor of 2. Both approaches using strain at fracture and MG failure strain can be used in predicting the creep failure under uniaxial and multiaxial features. The advantage of using MG strain is that the laboratory creep testing can be interrupted prior to specimen fractured or once the secondary creep deformation occurs. Meanwhile, the determination of strain at fracture needs longer test duration where the test can bestopped only when the specimen broken.