This paper examines the mechanical performance of steel/CFRP adhesively-bonded double strap joints at elevated temperatures around the glass transition temperature (
T
g
, 42
°C) of the adhesive. A ...series of joints with different bond lengths were tested to failure at temperatures between 20
°C and 60
°C. It was found that the joint failure mode changed from adherend failure to debonding failure as the temperature approached
T
g
. In addition, the ultimate load and joint stiffness decreased significantly at temperatures near to and greater than
T
g
, while the effective bond length increased with temperature. Based on the ultimate load prediction model developed by Hart-Smith for double lap joints and kinetic modelling of the mechanical degradation of the adhesive, a mechanism-based model is proposed to describe the change of effective bond length, stiffness and strength degradation for steel/CFRP double strap joints at elevated temperatures. The modelling results were validated by the corresponding experimental measurements.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Although extensive studies of the bond between steel and CFRP under various environmental exposures have been carried out, the effects of UV have not been examined to date. This knowledge gap is ...addressed in this paper. Specimens (epoxy adhesive, CFRP laminates and steel/CFRP adhesively-bonded joints) were exposed to UV for various time periods and identical reference specimens were exposed to only thermal environments without UV. It was found that UV exposure does not influence the tensile strength of CFRP composites. The tensile strength of the adhesive reduced by 13.9% while modulus showed a significant increase by 105% after 744h of exposure. The tensile modulus of adhesive exposed to only thermal environment also increased by 38%, considerably less than that induced by UV exposure. The UV exposure also led to a decrease in joint strength but an increase in stiffness, caused by the temperature effect rather than the UV rays.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Let X$X$ be a compact Kähler manifold of dimension n$n$ and ω$\omega$ a Kähler form on X$X$. We consider the complex Monge–Ampère equation (ddcu+ω)n=μ$({dd^c}u+\omega )^n=\mu$, where μ$\mu$ is a ...given positive measure on X$X$ of suitable mass and u$u$ is an ω$\omega$‐plurisubharmonic function. We show that the equation admits a Hölder continuous solution if and only if the measure μ$\mu$, seen as a functional on a complex Sobolev space W∗(X)$W^*(X)$, is Hölder continuous. A similar result is also obtained for the complex Monge–Ampère equations on domains of Cn$\mathbb {C}^n$.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
In this study UiO-66 and UiO-66-NH2 were synthesized by solvothermal method. The effect of preparation conditions on the quality of UiO-66-NH2 was studied. The obtained material has been ...characterized by x-ray diffraction (XRD), infrared spectroscopy (IR), thermogravimatric analysis (TGA), scanning electron microscopy (SEM) and nitrogen physisorption measurements (BET). The CO2 and CH4 physisorption measurements were carried out using a high pressure volumetric analyzer (Micromeritics HPVA-100). The results showed that the UiO-66-NH2 of ball shape crystalline had been obtained and characterized by high surface area (BET) up to 876 m2 g−1, specific volume 0.379 cm3 g−1, pore radius 9.5 Å and thermal stability up to 673 K, respectively. The experiments indicated that in comparison with UiO-66 the addition of NH2 is able to increase the CO2 and CH4 storage capacity at 1 bar and 303 K twice from 28.43 cm3 g−1 up to 52 cm3 g−1 and from 6.68 cm3 g−1 to 11.1 cm3 g−1, respectively.
Molecular dynamics simulation, which is considered an important tool for studying physical and chemical processes at the atomic scale, requires accurate calculations of energies and forces. Although ...reliable energies and forces can be obtained by electronic structure calculations such as those based on density functional theory this approach is computationally expensive. In this study, we propose a full-stack model using a deep neural network (NN) to enhance the calculation of force and energy. The NN is designed to extract the embedding feature of pairwise interactions of an atom and its neighbors. These are aggregated to obtain its feature vector for predicting atomic force and potential energy. By designing the features of the pairwise interactions, we can control the performance of models. We also consider the many-body effects and other physics of the atomic interactions. Moreover, using the Coulomb matrix of the local structures in complement to the pairwise information, we can improve the prediction of force and energy for silicon systems. Furthermore, the transferability of our models to larger systems is confirmed with high accuracy.
Display omitted
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
► Detailed comparative study on environmental, loading and curing effects. ► Harsh environments represented by cyclic temperature and humidity, combined with loading. ► Curing effects on durability ...of the adhesively-bonded system is quantified. ► Creep response under cyclic temperature and humidity received up to 270h. ► Time-to-failure in a harsh environment quantified as a function of load level.
This paper examines the effects of curing conditions on the performance of steel/CFRP double strap joints subjected to combined loading, cyclic temperature and humidity. A series of joints, cured respectively at an elevated temperature (120°C) and room temperature (about 23°C) were exposed to different combined environmental and loading conditions. It was found that curing at an elevated temperature had no effects on the joint ultimate strength tested at room temperature. However, at 50°C, the joints cured at 120°C showed almost no strength reduction, in comparison to those cured at room temperature with a 50% strength reduction. Curing at elevated temperature also helped to improve the time-to-failure of joints: joints cured at room temperature failed within less than 2h when exposed to the environmental conditions, while joints cured at 120°C could survive up to 270h, dependent on the applied load levels. Partial safety factors proposed in design guidelines for FRP composites under environmental effects were used to evaluate the experimental results obtained, suggesting a very critical degradation of joint mechanical properties due to the environmental effects investigated in this study.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
No-cook process or Simultaneous Liquefaction, Saccharification, and Fermentation process (SLSF) under very-high-gravity (VHG) condition possesses many advantages for potable ethanol production from ...rice. The important nutrient that affects the effectiveness of fermentation is nitrogen. Two sources of nitrogen are considered including added urea and indigenous rice protein which can be hydrolysed by an external protease. This study aims to assess the impact of urea and protease on rice conversion, yeast performance including the formation of ethanol and co-products in the SLSF-VHG. The results show that in comparison to the control process (without adding nitrogen), a protease (Fermgen™ 2.5X) supplementation of 600 SAPU/kg rice flour resulted in efficient breakdown of the rice structure along with 2.4% v/v higher ethanol yield and shorter fermentation time of 48 h. Meanwhile, the adding urea at concentration of 16 mM had a slight effect on the structural modification of the rice material without a significant increase (p < 0.05) of final ethanol yield. There was no significant difference (p < 0.05) in ethanol yield between urea and protease addition compared with protease alone. Our results suggested that the addition of protease provided enough nitrogen for yeast by hydrolysing the endogenous rice protein during SLSF-VHG process.
Display omitted
•Protease significantly affected the growth and size of yeast as well as structure and shape of rice.•Protease addition enhanced ethanol content by 2.40% v/v and shortened fermentation time by 48 h.•SLSF-VHG process from rice did not require any external nitrogen addition.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Degradation of structural adhesives at elevated temperatures makes the time-dependent behaviour of adhesively-bonded steel/CFRP joints a critical issue for safety considerations of CFRP strengthened ...steel structures. This paper reports the examination of specimens at different load levels (i.e. 80%, 50%, and 20% of their ultimate load measured at room temperature) and constant temperatures from 35°C to 50°C (i.e. temperatures below and above the glass transition temperature Tg, 42°C of the adhesive). Furthermore, a scenario of cyclic thermal loading between 20°C and 50°C was included to represent more realistic exposure. Joint time-dependent behaviour was demonstrated by the stiffness and strength degradation as a function of not only temperature but also time. At the same temperature level close to or above Tg, a higher load level corresponded to a shorter time-to-failure. In addition, up to 47% of strength recovery was found for the specimens subjected to cyclic temperatures compared with those under constant 50°C which failed at the same load level. Based on the proposed temperature and time-dependent material property models, the time-dependent failure time of steel/CFRP double strap joints was well described and validated by the experimental results.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
In order to make 2nd-generation biofuels more competitive, high solid-matter content has to be reached. To progress towards this target, the mechanism for destructuring lignocellulose fibres in ...semidilute conditions has to be well understood, as this configuration shows the basic mechanism which limits transfers and efficiency. This study aims to delve deeply into the biophysical and transfer limitations occurring during enzymatic hydrolysis. A specific experimental set-up associating in-situ and ex-situ physical (rheometry, chord length analysis) and biochemical analysis was used to expand the knowledge of hydrolysis of extruded softwood paper pulp over 24 h under different substrate concentrations (1%–3%) and enzyme doses (Accellerase 1500, 5 and 25 FPU/g cellulose). Non-Newtonian behaviour associated with pronounced yield stress stand as the major factors limiting process efficiency. A critical time was deduced from viscosity evolution, and the existence of a unique, dimensionless viscosity-time curve was established, suggesting similar mechanisms for fibre degradation. In addition, chord length distribution allowed for the description of population evolution and was discussed in the light of in-situ viscosity and hydrolysis yield. Physical (viscosity, particle size) and biochemical (substrate) kinetics were modelled (second-order) and coefficients identified. A chronology of the encountered phenomenological limitations demonstrates the necessity of optimising bioprocesses by considering physical parameters. A reference feed rate is proposed in order to reach high solid loading under fed-batch strategy.
•An in- & ex-situ multiscale approach was used to study the paper pulp hydrolysis.•The bio-physical and transfer limitations during hydrolysis were investigated.•A non-Newtonian behaviour was the major factor limiting process efficiency.•A unique dimensionless viscosity-time curve was identified.•A reference feed rate is proposed to reach high solid loading with fed-batch mode.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Chemical degradation in the presence of H2O2 aqueous solution and water states of poly(styrene sulfonic acid) (PSSA) grafted poly(ethylene‐co‐tetrafluoroethylene) polymer electrolyte membranes ...(ETFE‐PEMs) with grafting degree (GD) of 8.8%–21.1% are investigated using Fourier‐transform infrared spectroscopy (FT‐IR), thermogravimetric analysis (TGA), and electrochemical impedance spectroscopy (EIS). The ETFE‐PEMs show the complete detachment at the α‐hydrogen atoms of the whole graft PSSA chains from the ETFE backbones, while their precursor polystyrene‐grafted ETFE films do not. This chemical degradation exhibits independently with GDs and takes place even at very low GD (<10%). Water molecules of the membranes dried at 40°C are not completely de‐absorbed. The remains are partial non‐bonded water molecules, which are assumed to locate within the lamellar amorphous domains (constrained water molecules) of the crystalline phases. These constrained water molecules exist independently with the PSSA groups and do not detach together with them during the degradation. Note that the water molecules remained at 40°C show the additional contribution of 18%–19% to the total water uptake but do not contribute clearly to the conductance.
The water states and locations under the effects of temperatures are illustrated in the figure. The constrained water molecules remained at 40°C show the additional contribution to the total water uptake but do not contribute clearly to the conductance.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
PDF
