Environmental Aging Conditions Research Articles

Effect of heat aging on pull-off strength of FRP epoxy bonded concrete: An experimental study and fire modelling

In this study, the bonding strengths of three different types of externally bonded composite systems were investigated under different environmental aging conditions at high temperatures, and the finite element model for a roof fire and concrete slab fire from above evaluated if the beams were externally reinforced with fiber-reinforced polymers (FRP). An FRP system is a structural reinforcement made of a type of fiber reinforcement fixed to a concrete surface through an epoxy adhesive. The bonding strength between the FRP and concrete substrates was measured using a pull-off test machine, as described in the EN 1542 standard. This study aims to determine the deterioration and negative effects of miscellaneous high temperatures on externally bonded FRPs used for strengthening civil structures. Epoxy-bonded carbon fiber-reinforced polymers (CFRP), glass fiber-reinforced polymers (GFRP), and basalt fiber-reinforced polymers (BFRP) were exposed to various temperatures of 23°C (control conditions), 70, 85, 100, 115, 130, and 150°C. Duratek® AV21 epoxy-based lamination system was used as an adhesive between the concrete and the FRP sheet. Three bonding failure modes (adhesive, cohesive, and substrate) were investigated for each test. The results were compared for three different types of FRPs under various temperatures, which is also significant research on the heat aging of the degradation process. The test results were also evaluated using finite element (FE) software modelling for roof and slab fires exposed from above, where the beams under the slab were reinforced with FRP systems. The test pull-off test results and FE model thermal analysis results were evaluated to obtain the temperature rise in the critical section of the concrete beam/slab in existing retrofitted buildings. The FE model results showed a critical temperature rise on the beam-slab corner connection as a result of the fire above the concrete slab. The duration of the FRP systems effectively bonded to the concrete beams located under different slab thicknesses and pull-off results were evaluated at elevated temperatures.

Ecotoxicity of tire wear particles to antioxidant enzyme system and metabolic functional activity of river biofilms: The strengthening role after incubation-aging in migrating water phases

Tire wear particles (TWPs) are commonly studied for their exudation toxicity, yet a critical knowledge gap exists regarding the source nature and migration of these particulate pollutants, hindering comprehensive environmental risk assessments. This study explores the pristine properties of three typical TWPs (rolling friction (R-TWPs), sliding friction (S-TWPs), and cryogenically milled tire treads (C-TWPs)) and their aging characteristics after incubation in runoff (primary aging) and sewage (further aging). Our investigation aims to unveil the intrinsic mechanisms of TWPs ecotoxicity towards freshwater biofilms. Results reveal that the generation modes significantly impact pristine physicochemical properties, including surface structure, particle size, and EPFR abundance. These factors, in turn, influence acute ecotoxicity, as evidenced by cell mortality, antioxidant enzyme activity responses, and metabolic changes in freshwater biofilms. The ecological toxicity ranking of pristine exposure groups is S-TWPs, R-TWPs, and C-TWPs, attributed to variations in surface properties and particle size. Following incubation and aging, especially in sewage, differences in physicochemical properties among TWPs types diminish. Alarmingly, ecotoxicity intensifies and becomes consistent across TWPs types, driven by the screening of small particles during water incubation aging and the formation of EPFRs on TWPs surfaces stimulated by photosensitive organic matter or groups. This study underscores the aquatic ecological risks associated with TWP surface properties, highlighting the significant influence of environmental aging conditions on these risks.

Anti-Environmental Aging Passive Daytime Radiative Cooling.

Passive daytime radiative cooling technology presents a sustainable solution for combating global warming and accompanying extreme weather, with great potential for diverse applications. The key characteristics of this cooling technology are the ability to reflect most sunlight and radiate heat through the atmospheric transparency window. However, the required high solar reflectance is easily affected by environmental aging, rendering the cooling ineffective. In recent years, significant advancements have been made in understanding the failure mechanisms, design strategies, and manufacturing technologies of daytime radiative cooling. Herein, a critical review on anti-environmental aging passive daytime radiative cooling with the goal of advancing their commercial applications is presented. It is first introduced the optical mechanisms and optimization principles of radiative cooling, which serve as a basis for further endowing environmental durability. Then the environmental aging conditions of passive daytime radiative cooling, mainly focusing on UV exposure, thermal aging, surface contamination and chemical corrosion are discussed. Furthermore, the developments of anti-environmental aging passive daytime radiative cooling materials, including design strategies, fabrication techniques, structures, and performances, are reviewed and classified for the first time. Last but not the least, the remaining open challenges and the insights are presented for the further promotion of the commercialization progress.

Investigation of the deleterious effects of low-temperature and hygrothermal aging conditions on the mixed-mode fracture resistance of epoxy resin using a short-beam bend specimen

The effect of different environmental aging conditions on the mixed-mode fracture behavior of epoxy resins was investigated using a sub-size specimen. The short-beam bend (SBB) specimens with different crack inclination angles were manufactured and subjected to low-temperature (-71 °C), hygrothermal (immersion in deionized water at 60 °C) and room-temperature conditions. The deleterious effect of low-temperature and hygrothermal aging conditions on the mode-I, mode-II and mixed-mode I/II fracture responses of the epoxy resin was studied by testing the aged and unaged SBB specimens under three-point bend loading. The experimental results indicated that the hygrothermal aging condition, with a reduction of 49% in the effective fracture toughness, imposed a more severe deleterious effect on the fracture response of the specimens in comparison with the low-temperature condition with a decrease of 35% in the effective fracture toughness. The generalized maximum tangential stress criterion was used to predict the fracture loads of the aged and unaged specimens. Moreover, optical microscopy and scanning electron microscopy techniques were employed to assess the fracture surfaces of the specimens aged under different conditions.

Development of a Robot for In-service Radiography Inspection of Subsea Flexible Risers

The extreme operational environmental conditions and aging conditions of subsea structures pose a risk to their structural integrity and is critical to their safety. Nondestructive testing is essential to identify defects developing within the structure, allowing repair in a timely manner to mitigate against failures that cause damage to the environment and pose a hazard to human operators. However, to be cost effective, inspections must be carried out without taking the risers out of service. This poses significant safety risks if undertaken manually. This paper presents the development of an automated inspection system for flexible risers that are used to connect wellheads on the seafloor to the offshore production and storage facility. Due to the complex structure of risers, radiography is considered as the best technique to inspect multiple layers of the risers. However, radiography inspection, in turn, requires a robotic system for in-situ inspection with higher payload capacity, precise movement of source and detector which is able to withstand an extreme operational environment. The deployment of a radiography inspection system has been achieved by developing a customized subsea robotic system called RiserSure that can provide precise scanning motion of a gamma ray source and digital detector moving in alignment. The prototype has been tested on a flexible riser during shallow water sea trials with the system placed around a riser by a remotely operated vehicle. The results from the trials show that the internal inner and outer tensile armor layer and defects in the riser can be successfully imaged in real operational conditions.

Effect of hygrothermal and alternating load coupled aging on CFRP/Al bonded joints

The fracture failure of bonding structures is closely related to aging environment, so it is of great significance to study the effect of hygrothermal and alternating load coupled aging on bonding structures. Referring to the actual service environment of the vehicle, we formulated three kinds of artificial accelerated aging conditions, including temperature cycle, high temperature and high humidity and hygrothermal cycle. CFRP (Carbon Fiber Reinforced Plastic)/Al butt joints were selected as research object. Under these conditions, after aging for 0 day, 5 days, 10 days, and 15 days, respectively, quasi-static tensile tests were carried out to analyze the failure strength and failure modes of the joint. Through FTIR (Fourier Transform Infrared Spectroscopy) and DSC (Differential Scanning Calorimeter) tests of the CFRP and adhesive before and after aging, the change law of material chemical properties after environment aging was studied, and the influence mechanism of hygrothermal environment on joint was discussed. All three environmental aging conditions were coupled with alternating load, and the accelerated aging tests of joints were carried out to obtain the aging law. Combined with the two factors analysis of variance, the influence degree of different factor on joint strength in coupled aging was quantitatively studied respectively. The results showed that the failure strength of the joint will decrease rapidly and then slowly as aging time went by. Furthermore, with the introduction of alternating load, the decrease of joint failure strength became faster, which was mainly due to the degradation of the adhesive layer and the damage of the adhesive/substrate interface. Under the conditions of hygrothermal coupled with alternating load, the damage mainly occurred in the adhesive layer. Among these three coupled aging conditions, the condition of hygrothermal cycle coupled with alternating load has the worst influence on the joint strength, followed by the high temperature and high humidty coupled with alternating load, and the temperature cycle coupled with alternating load has the least influence on the joint strength.

The color stability of maxillofacial silicones: A systematic review and meta analysis.

Aim:This systematic review aims to identify and interpret results of studies that evaluated the changes in the color stability of maxillofacial prosthetic materials due to chemical instability of silicones and pigments and the effect of exposure to environmental conditions and aging factors on the same.Settings and Design:This systematic review was conducted in accordance with the Preferred Reporting Items for Systematic reviews and Meta-Analyses guidelines (PRISMA).Materials and Methods:Relevant articles written in English only, before November 15, 2019, were identified using an electronic search in the PubMed/Medline conducted to identify pertinent articles. The relevancy of the articles was verified by screening the title, abstract, and full text, if they met the inclusion criteria. A total of 42 articles satisfied the criteria, from which data were extracted for qualitative synthesis. This review protocol was registered in the International Prospective Register of Systematic Reviews (PROSPERO registration number CRD42019124562).Statistical Analysis Used:Since considerable data heterogenicity was present in all studies except the ones on incorporation of TiO2 for which meta-analysis using random effects model was performed.Results:The database search resulted in 234 studies, of which 202 articles were excluded due to lack of relevance, duplication, and unavailability of data. The remaining 32 fulltext articles were assessed for eligibility, out of which 2 articles were excluded. Twelve articles were yielded by manual search. A total of 42 studies were included in the present systematic review. Due to heterogeneous data, meta-analysis could be only carried out with the effect of TiO2 nano particle on color stability.Conclusions:Although there has been extensive amount of research in this field, an ideal maxillofacial silicone exhibiting good color stability in various human and environmental aging conditions is yet to be identified. Human and environmental aging conditions have an adverse effect on the color stability and addition of TiO2 nano particle seems to improve the same.

Performance of Mechanical Joints Prepared from Carbon-Fiber-Reinforced Polymer Nanocomposites under Accelerated Environmental Aging

The influence of environmental aging on the durability of the civil structural components made of fiber/epoxy composites is a big concern for many industries nowadays. For that reason, accelerated environmental aging was performed on the bolted joints prepared from carbon/epoxy composites. The bolted joints were designed using ASTM D 5961 having an edge to diameter ratio and width to diameter ratio as 5 and 6, respectively. The cyclic exposure of ultraviolet radiation for 8 h at 60 °C and condensation for 4 h at 50 °C was used under accelerated environmental aging conditions according to ASTM G154 standard for 0, 250, 500, 750 and 1000 h. It was found that at shorter durations, the positive effect occurred with increased strength, whereas the strength decreased for longer durations. The failure loads were found for neat and multi-walled carbon nanotube (MWCNT) added composite bolted joints for unaged and aged conditions at varying bolt preloads. The MWCNT added composites shows better results than neat composites. It was also observed that bolt preloads improved the load-bearing capacity for MWCNT added composite joints even after 1000 h of accelerated aging.

Effect of environmental aging on mechanical properties of graphene nanoplatelet/nanocarbon aerogel hybrid-reinforced epoxy/carbon fiber composite laminates

In this study, graphene nanoplatelet (GNP)/nano-carbon aerogel (NCA) hybrids were used to reinforce epoxy/carbon fiber composite (CFRP) laminates to investigate the environmental aging effect on their mechanical properties. Different amounts (i.e., 0, 0.25, 0.5, 0.75, and 1.0 wt%) of the GNP/NCA (1:1) hybrids were dispersed in epoxy resin to prepare GNP/NCA/CFRP laminates. The mechanical properties of these reinforced laminates were investigated under three different environmental aging conditions (i.e., 25 °C, 65% relative humidity (RH); 25 °C, 85% RH; and 85 °C, 85% RH). Furthermore, the micro-mechanisms were examined under the environmental aging conditions for improved mechanical properties of the GNP/NCA/CFRP laminate. The impacts of various environmental parameters, i.e., temperature and moisture, were discussed. The reinforced laminates showed better mechanical properties than neat laminates under all three environmental aging conditions. Based on the published results and the experimental results obtained herein, the mechanisms of the GNP/NCA hybrid-reinforced CFRP laminate were defined.

Application of Fieldbus Technology to Enable Enhanced Actuator Control of Automated Inspection for Offshore Structures

Due to extreme environmental loadings and aging conditions, maintaining structural integrity for offshore structures is critical to their safety. Non-destructive testing of risers plays a key role in identifying defects developing within the structure, allowing repair in a timely manner to mitigate against failures which cause damage to the environment and pose a hazard to human operators. However, in order to be cost effective the inspection must be carried out in situ, and this poses significant safety risks if undertaken manually. Therefore, enabled by advancements in automation and communication technologies, efforts are being made to deploy inspection systems using robotic platforms. This paper proposes a distributed networked communication system to meet the control requirements of a precision rotary scanner for inspection of underwater structures aimed at providing a robotic inspection system for structural integrity in an offshore environment. The system is configured around local control units, a fieldbus network, and a supervisory control system accounting for the environment conditions to provide enhanced control of actuators for automated inspection of offshore structures.

Effect of environmental aging conditions on the properties of fly ash filled epoxy composites

The effect of environmental aging conditions on the structural and mechanical properties of fly ash (FA) filled epoxy composites with four different volume fraction of FA (i.e. 0.1, 0.2, 0.3 and 0.4) has been investigated under four aggressive aging environments and aging periods. The crystallite size and microstrain of crystalline particle in the composite matrix is quantified from XRD analysis. The 10% FA filled epoxy composite under fuel solution retains the higher order of crystallinity and glass transition temperature. It is observed that the void content and actual density of composites decreases with increasing FA content. The mechanical behavior of FA epoxy composite deteriorated with increasing aging duration and reinforcement percentage. 10% FA-containing specimen gives the highest mechanical properties under fuel environment for any given aging duration. The 20% FA filled epoxy composite can also be used in low load bearing applications.

The Effect of MBS Toughening for Mechanical Properties of Wood-Plastic Composites under Environmental Ageing

Wood–plastic composites (WPCs) are a promising environmentally friendly material refers to composite that contain plant powders or fibers as reinforcement and plastic matrix. In this study, an epoxy resin and Methyl metharylate-Butadiene-Styrene Copolymer (MBS) were used as a compatibilizer and toughener and were filled into recycled polyethylene terephthalate (PET) and recycled polyamide 6 (PA6) blends (PET/PA6) and filled with wood flour to prepare the WPCs. The mechanical properties of the WPCs, including the tensile, flexural, and impact properties, with different mixing ratio polymer blends of PET to PA6 (E60/A40, E50/A50, and E40/A60) were investigated under different environmental aging conditions. The experimental results showed that different environmental conditions, such as temperature and humidity, markedly changed the mechanical properties of the WPCs with different mixing ratio polymer blends. In addition, the mechanisms responsible for the interface of the WPCs were identified by studying the fracture surfaces with field emission scanning electron microscopy.

Effects of hygrothermal aging on glass-fibre reinforced polymer laminates and adhesive of FRP composite bridge: Moisture diffusion characteristics

Moisture absorption and hygrothermal aging in glass-fibre-reinforced polymer laminates and a structural adhesive of FRP composite bridge are studied. By gravimetric experiments, the moisture diffusion in GFRP laminates and adhesive is characterised in four environmental aging conditions (20°C–50% RH (relative humidity), 20°C–water, 40°C–96% RH and 40°C–water). Based on the analytical models from 1D and 3D moisture diffusion theories, the moisture diffusion coefficients are determined by the best least-square curve fitting to experimental data. Finite Element models are further developed, which subsequently validate the analytically obtained moisture diffusion coefficients. The FE analysis indicates that, for identification of 3D moisture diffusion coefficients of anisotropic FRP materials, the equivalent diffusion coefficient method is unreliable, and the 3D moisture diffusion theory is essential. Furthermore, mass loss is found for the Square and Rectangular specimens under 40°C–water condition. Polymer relaxation is observed for structural adhesive.

Inorganic/organic multilayer passivation incorporating alternating stacks of organic/inorganic multilayers for long-term air-stable organic light-emitting diodes

Inorganic/organic multilayer passivation films were fabricated in an effort to enhance the long-term air stability of an organic light-emitting diode (OLED). AlOx was used as an inorganic layer and 6.5 pairs of alternating silicon monoxide (SiO) and poly zinc acrylate (pZA) layers were used as the organic layers. The organic layers (Alternate stack of SiO and pZA layers) made it possible to decouple the defects present in the inorganic layer (AlOx) and to increase the penetration length of water and oxygen into the devices. The resulting film was characterized using transmission electron microscopy. The film displayed a high transmittance (>95%) and a low water vapor transmission rate (WVTR, 7.98×10−5g/m2 day) under accelerated environmental aging conditions (a temperature of 60°C and a relative humidity (R.H.) of 90%). In addition, The OLEDs did not incur significant damage caused by temperature (100°C) and plasma (100W) during fabrication process by depositing of SiO onto the OLED device prior to applying the passivation layers. The passivated OLED displayed a prolonged shelf-lifetimes over a period of 3000h at 60°C and 90% R.H.

Performance improvement by glass fiber of adhesively bonded metal joints at the cryogenic temperature

The performance of adhesively bonded joints composed of aluminum sheet and stainless steel foils was investigated at the cryogenic temperature for the secondary barrier LNG (Liquefied Natural Gas) containment system. Since the huge adhesive bonding area such as LNG carriers or floaters cannot be surface-treated economically by chemical treatment, new flame surface treatment method for the metal foils was evaluated and compared with other conventional surface treatments such as mechanical or chemical surface treatments at the cryogenic temperature. The surface wettability by contact angle measurement of the metal foil was investigated with respect to surface treatments and environmental aging conditions. The effects of adhesive thickness on the adhesive bond strength and fracture toughness have been also investigated at the cryogenic temperature.The experimental results showed that the bonding performances depended strongly on the surface treatment method, adhesive thickness and fiber reinforcement for the adhesive, such. It was also found that the thick adhesive joint had a reduced bonding strength at the cryogenic temperature, but the glass fiber reinforcement improved much the bonding strength and fracture toughness for thicker adhesive at the cryogenic temperature.

Effect of Extraoral Aging Conditions on Color Stability of Maxillofacial Silicone Elastomer

Maxillofacial prostheses require enhancement or replacement due to deterioration in their color during service. The purpose of this study was to investigate color stability of pigmented and nonpigmented maxillofacial silicone elastomer exposed to different human and environmental aging conditions. One hundred and twelve disk-shaped silicone (TechSil S25, Technovent, Leeds, UK) specimens were prepared and equally divided into pigmented (using intrinsic rose-pink skin shade, P409, Principality Medical, Newport, UK) and nonpigmented categories of seven groups (n = 16; 8 pigmented and 8 nonpigmented): dark storage (control) (group 1), sebum solution storage (group 2), acidic perspiration storage (group 3), light aging (group 4), natural outdoor weathering (group 5), silicone-cleaning solution (group 6), and mixed conditioning of sebum storage and light aging (group 7). Conditioning periods (groups) were 6 months (groups 1, 2, 3, 5), 360 hours (groups 4, 7), and 30 hours (group 6). Color change (ΔE) was measured at the start and end of conditioning. In addition, for groups 1, 2, and 4, ΔE was measured at fixed intervals of 30 days, 15 days, and 30 hours, respectively. Data were analyzed with one-way analysis of variance (ANOVA), Dunnett's-T3 post hoc, and independent t-tests (p < 0.05). Linear regression was implemented to investigate ΔE with time for groups 1, 2, and 4. Six of the seven treatment conditions induced perceivable color change (ΔE > 3). Within the nonpigmented category, specimens stored in the dark for 6 months (group 1) exhibited high ΔE (6.17), which was greater (p < 0.05) than that produced by silicone-cleaning solution for 30 hours (group 6) (ΔE = 2.08). Within the pigmented category, light aging (group 4), outdoor (group 5), and mixed (group 7) conditionings induced greatest color changes (ΔE = 8.26, 8.30, 9.89, respectively) (p < 0.05); however, there was a strong positive linear function of log-time after dark storage (group 1) and light aging (group 4). There is inherent color instability of nonpigmented silicone elastomer, which adds to the overall color change of silicone prostheses. Storing silicone elastomer in simulated sebum under light aging induced the greatest color changes. Overall, the color stability of TechSil S25 maxillofacial heat-temperature-vulcanizing (HTV) silicone elastomer was unacceptable (ΔE > 3.0, range from 3.48 to 9.89 for pigmented and 3.89 to 10.78 for nonpigmented) when subjected to six of the seven extraoral aging conditionings used in this study. Inherent color instability of nonpigmented facial silicone elastomers primarily contributes to the color degradation of extraoral facial prostheses. Sebaceous skin secretions along with daylight radiation cause the greatest perceivable color change to the silicone and pigment used in this study.

Impact of aging conditions on mechanical properties of thermoplastic polyurethane

In this study, impact of environmental aging conditions on the mechanical properties of thermoplastic polyurethane (TPU) was investigated. Especially, effect of temperature on water diffusion has been studied. Water-sorption experiments, tensile test and dynamic mechanical thermal analysis (DMTA) were performed after immersion in distilled water at different temperatures (25, 70 and 90 °C). The sorption process was analyzed by gravimetric measurements at different temperatures. Also, diffusion coefficients of solvent molecules in the TPU samples were identified. Therefore the activation energy and the mixing enthalpy were deduced. The aging impact on some mechanical properties of this material has been investigated after various aging cycles. Degradation of mechanical properties was observed. In fact, elastic modulus and stress at 200% of strain were decreased. It was also shown that such degradation largely depends on both aging temperature and aging immersion duration. The storage modulus ( E′) was also affected by the hygrothermal (HT) environment. The modification of mechanical properties seems to be well correlated to structural observations obtained from scanning electron microscopy (SEM) photographs. Finally, through thermal aging experiments, it was deduced that the combination of temperature with water seems to be a major factor of TPU degradation.

Environmental aging of polycyclic aromatic hydrocarbons on soot and its effect on source identification

Soot-associated PAHs were exposed to simulated sunlight to investigate disappearance rates under environmental aging conditions and to examine the robustness of diagnostic ratios for PAH source apportionment. Naphthalene, acenaphthylene, acenaphthene, and fluorene showed an obvious two-phase disappearance in all experiments while phenanthrene and anthracene exhibited this behavior for all but the highest soot loading. The first phase loss is 5–40 times faster than the second phase loss and occurred within 3 h for naphthalene, acenaphthylene, acenaphthene, and fluorene and within 10 h for phenanthrene and anthracene. Two-phase disappearance was not observed for any of the higher molecular weight PAHs with 4–6 rings. Each PAH has a unique loss rate via photodegradation and volatilization and these rates of some PAHs were affected by soot loadings; phenanthrene and anthracene showed similar rates in the first phase and increased loss rates in the second phase as soot loading increased. In the absence of light, the loss of PAHs was related to both temperature and molecular characteristics. Due to differences in disappearance rates of individual PAHs under illumination over extended times, prolonged exposure to sunlight could change the interpretation of some diagnostic ratios used previously for PAH source identification. This result indicates that more consistent and accurate methods that take into consideration the longevity of particulate PAHs are needed for reliable source apportionment.

The effect of ultraviolet radiation on sodium-etched poly(tetrafluoroethylene) bonded to polyurethane elastomer

Peel strength values of sodium-etched poly(tetrafluoroethylene) film bonded to polyurethane substrates have been monitored and found to decrease as a function of exposure to ultraviolet radiation. Attenuated total reflectance (ATR) spectra were monitored on unbonded sodium-etched poly(tetrafluoroethylene) surfaces for the same environmental aging conditions and were found to vary significantly in the region of 1650 cm−1. Techniques are proposed to retard UV-initiated etch degradation and thereby prolong bond integrity.