Aging Conditions Research Articles

Macroscale connectome topographical structure reveals the biomechanisms of brain dysfunction in Alzheimer's disease.

The intricate spatial configurations of brain networks offer essential insights into understanding the specific patterns of brain abnormalities and the underlying biological mechanisms associated with Alzheimer's disease (AD), normal aging, and other neurodegenerative disorders. This study investigated alterations in the topographical structure of the brain related to aging and neurodegenerative diseases by analyzing brain gradients derived from structural MRI data across multiple cohorts (n = 7323). The analysis identified distinct gradient patterns in AD, aging, and other neurodegenerative conditions. Gene enrichment analysis indicated that inorganic ion transmembrane transport was the most significant term in normal aging, while chemical synaptic transmission is a common enrichment term across various neurodegenerative diseases. Moreover, the findings show that each disorder exhibits unique dysfunctional neurophysiological characteristics. These insights are pivotal for elucidating the distinct biological mechanisms underlying AD, thereby enhancing our understanding of its unique clinical phenotypes in contrast to normal aging and other neurodegenerative disorders.

Investigation of age-hardening behaviour of Al alloys via feature screening-assisted machine learning

Age hardening stands as a crucial strengthening process for aluminium (Al) alloys. However, determining the optimal ageing conditions has traditionally relied on resource-intensive trial-and-error methods. To streamline the design of Al alloys, this study introduces a novel feature screening-assisted machine learning (ML) approach to explore age-hardening behaviour across varying compositions and heat treatment parameters, focusing on yield tensile strength (YTS), ultimate tensile strength (UTS), and elongation (EL). A comprehensive pool of features, incorporating alloy composition and fundamental elemental properties, was generated to provide metallurgical insights for ML predictions. Subsequently, feature screening methodologies, including correlation analysis, feature elimination, and multi-objective genetic algorithm (MOGA), were employed to identify key features from the vast feature pool, balancing model complexity and prediction accuracy. Employing support vector regression models trained on these optimized feature sets, we demonstrate enhanced prediction accuracy for strength properties while maintaining model simplicity for EL, with minimal impact on accuracy. In addition, experimental results further validate the method's ability to reproduce ageing curves across all three mechanical properties for both commercialized and newly designed Al alloys.

Decoding Brain Development and Aging

Abstract The aging process induces a variety of changes in the brain detectable by magnetic resonance imaging (MRI). These changes include alterations in brain volume, fluid-attenuated inversion recovery (FLAIR) white matter hyperintense lesions, and variations in tissue properties such as relaxivity, myelin, iron content, neurite density, and other microstructures. Each MRI technique offers unique insights into the structural and compositional changes occurring in the brain due to normal aging or neurodegenerative diseases. Age-related brain volume changes encompass a decrease in gray matter and an increase in ventricular volume, associated with cognitive decline. White matter hyperintensities, detected by FLAIR, are common and linked to cognitive impairments and increased risk of stroke and dementia. Tissue relaxometry reveals age-related changes in relaxivity, aiding the distinction between normal aging and pathological conditions. Myelin content, measurable by MRI, changes with age and is associated with cognitive and motor function alterations. Iron accumulation, detected by susceptibility-sensitive MRI, increases in certain brain regions with age, potentially contributing to neurodegenerative processes. Diffusion MRI provides detailed insights into microstructural changes such as neurite density and orientation. Neurofluid imaging, using techniques like gadolinium-based contrast agents and diffusion MRI, reveals age-related changes in cerebrospinal and interstitial fluid dynamics, crucial for brain health and waste clearance. This review offers a comprehensive overview of age-related brain changes revealed by various MRI techniques. Understanding these changes helps differentiate between normal aging and pathological conditions, aiding the development of interventions to mitigate age-related cognitive decline and other symptoms. Recent advances in machine learning and artificial intelligence have enabled novel methods for estimating brain age, offering also potential biomarkers for neurological and psychiatric disorders.

Abiotic degradation and accelerated ageing of microplastics from biodegradable and recycled materials in artificial seawater

Microplastics (MPs) are considered one of the most widespread pollutants in all ecosystems worldwide. In the environment, MPs can undergo hydrolysis and/or oxidation, resulting in the release of low-molecular weight degradation products, along with additives, and adsorbed organic pollutants. In this study, the morphological, chemical, and thermal changes of microplastics obtained from two biodegradable plastics, polylactic acid and Mater-Bi®, and a recycled plastic, recycled-polyethylene terephthalate, were examined after accelerated ageing under photo-oxidative conditions in synthetic seawater in a Solarbox system, and after thermal treatment in the dark. Thermal properties were studied by thermogravimetric analysis, differential scanning calorimetry, and evolved gas analysis-mass spectrometry. Compositions and changes of chemical components of the polymers were evaluated by attenuated total reflection-Fourier transform infrared spectroscopy and pyrolysis-gas chromatography–mass spectrometry. The leachable fractions and degradation products released in synthetic seawater by degraded MPs were characterized by gas chromatography–mass spectrometry. This study allowed us to identify hydrolysis as the main degradation pathway of the polymers under analysis, and to characterize not only the oligomers and degradation products released in the water as a consequence of degradation, but also additives used in plastic item formulations. This study improves our understanding of these polymers' behavior under accelerated ageing conditions.

Nanoparticle integration in adhesive and hybrid single lap joints: effect on strength and fatigue life under environmental aging

Examining the mechanical performance of CFRP and aluminum samples subjected to environmental aging is crucial. Additionally, it is essential to develop methods to enhance their mechanical properties. This research investigates the impact of fullerene and single-walled carbon nanotubes (SWCNT) on the fatigue life and static strength of bonded and bonded/bolted joints. The study focuses on composite-to-composite (CTC) and composite-to-aluminum (CTA) substrates under three-point bending, both before and after hygrothermal aging. The samples were divided into four categories: (1) neat specimens, (2) specimens with added fullerene, (3) specimens with added SWCNT, and (4) specimens with a combination of 50% SWCNT and 50% fullerene. The experimental results indicated that the optimal nanoparticle ratio for bonded joints differs from that for bonded/bolted joints. Adding nanoparticles to the adhesive increased the fatigue life of SLJs, particularly in samples containing mixed particles and SWCNT. In some cases, nanoparticles amplified the effect of hygrothermal conditions, enhancing fatigue life further. The integration of nanoparticles into the adhesive and the use of bonded/bolted joints significantly improved joint strength, with the combination of both techniques yielding the best results. These modified joints offer a promising alternative to traditional joints in terms of strength and fatigue life. The study enhances understanding of the aging of adhesive and hybrid joints, especially dissimilar joints (composite to metal), and provides insights into their behavior under various environmental aging conditions. These methods show potential for optimizing joints and composite structures, improving durability, and reducing the likelihood of operational failures.

Evaluating Age-Friendly Health Care Approaches in Rural Primary Care Settings: A Multi-Case, Mixed-Methods Hybrid Type 2 Effectiveness-Implementation Study.

Maintaining and improving the health and well-being of older people in rural communities through integrated care is essential to address this cohort's frailty risk. The Indigo 4Ms Tool for health workers is a rural-specific approach to providing care that addresses the common conditions of ageing. With Australian government funding, five small rural health services are implementing the tool. This paper describes the protocol for a hybrid type 2 implementation-effectiveness study to evaluate the tool's impact on multidisciplinary comprehensive care planning and the implementation strategies that enhance the adoption and sustainability of the tool across diverse rural health settings.

Efficacy of Acacia Gum Biopolymer in Strength Improvement of Silty and Clay Soils under Varying Curing Conditions

Acacia gum (AG), a polysaccharide biopolymer, has been adopted to improve the strength of three cohesive soils by subjecting them to diverse environmental aging conditions. Being a polysaccharide and a potentially sustainable construction material, the AG yielded flexible film-like threads after 48 h upon hydration, and its pH value of 4.9 varied marginally with the aging of the stabilized soils. The soil samples for the geotechnical evaluation were subjected to wet mixing and were tested under their Optimum Moisture Content (OMC), as determined by the light compaction method. The addition of AG modified the consistency indices of the soils due to the presence of hydroxyl groups in AG, which also led to a rise in OMC and reduction in Maximum Dry Unit weight (MDU). The Unconfined Compressive Strength (UCS) and California Bearing Ratio (CBR) were determined under thermal curing at 333 K as well as on the same day of sample preparation. The least performing condition of the soil’s CBR was evaluated under submerged conditions after allowing the AG-stabilized specimens to air-cure for a period of 1 week. The UCS specimens tested after 7 days were subjected to the initial 7 days of thermal curing at 333 K. A dosage of 1.5% of AG yielded the UCS of 2530 kN/m2 and CBR of 98.3%, respectively, for the low compressible clay (LCC) after subjecting the sample to 333 K temperature for 1 week. The viscosity of the AG was found to be 214.7 cP at 2% dosage. Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), and average particle size determination revealed the filling of pores by AG gel solution, adsorption, and hydrogen bonding, which led to improvements in macroproperties.

Structural health monitoring of glulam structures: analysis of durability and damage mechanisms

In today’s environmental context, the use of glulam or Glued Laminated Timber (GLT) as an alternative to conventional building materials could reduce the carbon footprint of engineering structures. However, this material is sensitive to outdoor exposure with moisture content variations inducing internal stresses and cracks and high moisture content increasing the risks of decay. This study therefore focuses on the development of a protocol to evaluate the effect of climatic conditions on the mechanical performance of the material. For this purpose, GLT samples were equipped with embedded sensors. Moisture and deformation sensors can accurately track wet-dry (W/D) cycles and their effects on deformation at adhesive joints. Samples are stored outdoors and mechanical tests are carried out after 6 months of aging. The results show an average reduction in flexural strength of about 10% compared to unaged specimens. Shear tests on the adhesive joints show a decrease in strength of more than 20%. The study of the fracture mechanisms also indicates a link between the type of fracture and the aging conditions of the specimens. These tests also validated a monitoring protocol that will allow, in the long term, to evaluate the impact of these cycles on the mechanical performance of GLT.

HArmonyCa™ hybrid filler to restore connective tissue: An Italian real-life retrospective study.

Facial aging and dermal conditions may negatively influence the quality of life, leading patients to seek aesthetic procedures to restore a more satisfying appearance. HArmonyCa™ is a recently developed hybrid filler that combines the actions of the most common dermal fillers, hyaluronic acid (HA) and calcium hydroxylapatite (CaHA). This study investigates the efficacy and safety of HArmonyCa™ in patients affected by chrono- and photoaging and several facial skin conditions. One hundred and twenty-nine patients, affected by chrono- and photoaging, and skin conditions such as oily and acne-prone skin, rosacea, or scarring, were treated with HArmonyCa™. Injections followed the retrograde linear fanning technique. A physicians' consensus identified five optimal entry points. The physician and patients assessed treatment outcomes using the Global Aesthetic Improvement Scale (GAIS) 9 months after treatment (including immediate lift effect, skin firmness, and elasticity), and 3D images were taken for documentation. Adverse events (AEs) were evaluated immediately after the procedure and after 9 months. According to the physician's assessments, all patients displayed an improvement in facial appearance, particularly during movement, with the patients' evaluation showing agreement. Only minor AEs were reporte, which resolved spontaneously. Moreover, HArmonyCa™ treatment proved compatible with different medications and aesthetic procedures. This study shows that one treatment with HArmonyCa™ yields highly satisfactory outcomes in patients affected by skin conditions. For the first time, we show that HArmonyCa™ is a dynamic filler that improves facial laxity during movement. The treatment proved to be safe and fully compatible with other cosmetic procedures and medications.

Aging enhances pro-atrogenic gene expression and skeletal muscle loss following respiratory syncytial virus infection.

Aging and many age-related health conditions are associated with skeletal muscle loss. Furthermore, older adults are more susceptible to severe respiratory infections, which can in turn lead to muscle wasting. The mechanisms by which respiratory viral infection can impact skeletal muscle in older adults are not well understood. We determined the effects of acute infection with respiratory syncytial virus (RSV) on the lung and skeletal muscle of aged mice. RSV infection caused more severe disease in aged mice with enhanced weight loss, reduced feeding, higher viral load, and greater airway inflammation. Aged but not young mice showed decreased leg muscle weight at the peak of illness and decreased size of leg muscle fibers. Aged mice increased muscle-specific expression of atrophy-promoting enzymes (Atrogin-1 and MuRF-1) and failed to increase the rate of muscle protein synthesis during RSV infection. In aged mice, the changes in Atrogin-1 and MuRF-1 gene expression in skeletal muscle correlated with IL-6 levels in the lungs. These findings indicate that RSV infection of aged mice provides a model for studying the diverse adverse systemic consequences of respiratory viral infections on health and wellbeing in older adults.

Design and Performance of Small-Molecule Donors with Donor-π-Acceptor Architecture Toward Vacuum-Deposited Organic Photovoltaics Having Heretofore Highest Short-Circuit Current Density.

The development of high-performance organic photovoltaic materials is of crucial importance for the commercialization of organic solar cells (OSCs). Herein, two structurally simple donor-π-conjugated linker-acceptor (D-π-A)-configured small-molecule donors with methyl-substituted triphenylamine as D unit, 1,1-dicyanomethylene-3-indanone as A unit, and thiophene or furan as π-conjugated linker, named DTICPT and DTICPF, are developed. DTICPT and DTICPF are facilely prepared via a two-step synthetic process with simple procedures. DTICPF with a furan π-conjugated linker exhibits stronger and broader optical absorption, deeper highest occupied molecular orbital (HOMO) energy levels, and better charge transport, compared to its thiophene analog DTICPT. As a result, vacuum-deposited OSCs based on DTICPF: C70 show an impressive power conversion efficiency (PCE) of 9.36% (certified 9.15%) with short-circuit current density (Jsc) up to 17.49mA cm-2 (certified 17.56mA cm-2), which is the highest Jsc reported so far for vacuum-deposited OSCs. Besides, devices based on DTICPT: C70 and DTICPF: C70 exhibit excellent long-term stability under different aging conditions. This work offers important insights into the rational design of D-π-A configured small-molecule donors for high efficient and stable vacuum-deposited OSCs.

A study on microstructure evolution of MCrAlY coatings after thermal aging in Te environment

The effects of thermal exposure on tellurium (Te) diffusion behavior in MCrAlY coatings were investigated at 800 °C in Te vapor. The results showed that the diffusion depth of Te in MCrAlY coatings gradually increased with the exposure time, and the dense Cr3Te4 layer formed on the coating surface in the initial stage was no longer continuous, especially under aging conditions with higher Te concentration. The high Cr content of the coating promoted the solid phase transition of the surface reaction product from Cr3Te4 to Cr7Te8, and resulting in the formation of large α-Cr phase either within or beneath the reaction layer during long aging processes. As a result of this phase transition, excess Te atoms were released from Cr3Te4 and continued to diffuse into the coating. Te did not exhibit obvious intergranular diffusion characteristics within the coating. When it encountered Y, it was captured by Y and formed a YTe phase. After aging for 3000 h, Te was distributed throughout the coating, and numerous voids were formed at the interface between the coating and the substrate. These two factors deteriorated the plasticity and adhesion of the coating. Results from molten salt corrosion tests indicated that the high content of Cr and Al in the coating, as well as high densities of grain boundaries providing diffusion pathways, reduced the corrosion resistance of the coating to molten salt.

Metabolic syndrome is associated with reduced default mode network functional connectivity in young post-9/11 Veterans.

Metabolic syndrome is a collection of health factors that increases risk for cardiovascular disease. A condition of aging, metabolic syndrome is associated with reduced brain network integrity, including functional connectivity alterations among the default mode, regions vulnerable to neurodegeneration. Prevalence of metabolic syndrome is elevated in younger populations including post-9/11 Veterans and individuals with posttraumatic stress disorder, but it is unclear whether metabolic syndrome affects brain function in earlier adulthood. Identifying early effects of metabolic syndrome on brain network integrity is critical, as these impacts could contribute to increased risk for cognitive disorders later in life for Veterans. The current study examined whether metabolic syndrome and its individual components were associated with default mode functional connectivity. We also explored the contribution of posttraumatic stress disorder and traumatic brain injury on these metabolic syndrome-brain relationships. Post-9/11 Veterans with combat deployment history (95 with and 325 without metabolic syndrome) underwent functional magnetic resonance imaging to capture seed-based resting-state functional connectivity within the default mode. The metabolic syndrome group demonstrated reduced positive functional connectivity between the posterior cingulate cortex seed and the bilateral superior frontal gyrus. Data-driven analyses demonstrated that metabolic syndrome components, particularly cholesterol and central adiposity, were associated with widespread reductions in default mode network connectivity. Functional connectivity was also reduced in participants with metabolic syndrome but without current posttraumatic stress disorder diagnosis and with traumatic brain injury history. These results suggest that metabolic syndrome disrupts resting-state functional connectivity decades earlier than prior work has shown.

Provision of prostate cancer services in Tanzania: perspectives from five tertiary hospitals

BackgroundAccess to quality prostate cancer services remains a global challenge, particularly in Low- and Middle-Income countries. This is often due to weak health systems that struggle to meet the population’s needs. The provision of quality health services to patients with prostate cancer requires a comprehensive approach involving multiple stakeholders and structural inputs. However, few studies have comprehensively assessed the relationship between these structural inputs and prostate cancer treatment outcomes. This study, therefore, aimed to determine the availability of selected structural inputs and descriptions of how they influence the provision of quality services to patients with prostate cancer in Tanzania.MethodsWe conducted a cross-sectional study using an explanatory sequential mixed-method approach to collect data from five tertiary hospitals providing cancer services in Tanzania. A validated checklist was used to collect information on available structural inputs for prostate services at tertiary hospitals. A semi-structured interview guide was used to conduct 42 in-depth interviews with 20 healthcare providers, five hospital managers, and 17 patients undergoing treatment for prostate cancer. Descriptive analysis was performed for the quantitative data, and thematic analysis was conducted with the aid of NVivo 14 qualitative software for the interview transcripts.ResultsAll five assessed tertiary hospitals had inadequate human resources for health to provide prostate cancer services. Only one had 70% of the required HRH, while none had above 40% of the required HRH. Within the hospitals, the skill mix imbalance was severe across cadres. Five themes emerged: inadequate infrastructure, delays in diagnosis, delays in treatment, shortage of human resources for health (HRH), and inefficient organization of prostate cancer services.ConclusionThe findings of this study, underscore the major health system deficiencies for the provision of prostate cancer services in tertiary hospitals. With the increased aging population, strong health systems are vital in addressing conditions of old aging, including prostate cancers. Studies on optimization of the available HRH and infrastructure are needed to improve the provision of prostate cancer in tertiary hospitals as an interim solution while long-term measures are needed for improving the HRH availability and conducive infrastructure.

Evolution mechanism of Mo-rich, B2-NiAl, and Cu-rich particles under aging and its influence on strength and elongation in a maraging hot work steel SDH88

A novel maraging hot work steel, SDH88, is developed to achieve a balance between ultimate tensile strength (UTS), yield strength (YS), and elongation by combining nanometer-scale precipitates of B2-NiAl, Cu-rich, and M2C carbide. The peak-aging sample demonstrates a YS of ∼1281.8 MPa, a UTS of ∼1665.9 MPa, and an elongation (EL) of ∼17.5 % at room temperature. The microstructure and precipitation changes from peak aging (8h) to over-aging (48h) were examined using different techniques. Under peak aging condition, the precipitates consist of four nanoparticles: 9R-Cu, B2-NiAl, Cu-NiAl, and M2C carbides. However, at over-aging condition, the type of particles changes and consist of B2-NiAl, M6C, Laves phases and FCC-Cu. This study systematically investigates the precipitation evolution of Mo-rich, B2-NiAl, and Cu-rich particles from peak-aging to over-aging conditions. The high YS at peak aging condition is attributed to high precipitation strengthening of ∼553.3 MPa and dislocation strengthening of about 430.8 MPa. The number densities of NiAl (<3.8 nm) particles are more than that of Cu particles which indicates that the NiAl nanoparticles are the dominant strengthening phase. Finally, this work clearly demonstrates that the new alloy composition design allows the application of aging steels in die casting steels with great advantages and potential for obtaining balanced mechanical properties through the systematic study of the aging process and mechanism of precipitation evolution. Proposing a new approach for designing hot work die steel without quenching treatment during mold processing.

Investigating thermal and UV ageing effects on crumb rubber modified bitumen enhanced with emission reduction agents and carbon black

Over time, bitumen experiences deterioration due to factors like the exposure to oxygen, solar irradiation, and temperature fluctuations. While laboratory techniques like rolling thin film oven (RTFO) and pressure ageing vessel (PAV) were developed to simulate field ageing, they do not accurately replicate environmental factors normally occurring in the field, particularly solar irradiation. Limited research has focused on understanding the ageing processes of crumb rubber modified bitumen (CRMB). This study investigated how different ageing conditions affect the chemo-rheological properties of CRMB and CRMB with geopolymer-based fly ash (GFA), Portland cement paste (PCP), and carbon black (CB). GFA and PCP were added to reduce noxious fumes and VOC emissions from CRMB whereas CB is commonly employed as an antioxidant agent. RTFO and PAV were used to simulate short- and long-term ageing, while a SUNTEST XLS+ weatherometer was used for thermal and UV ageing simulations. A dynamic shear rheometer and attenuated total reflectance Fourier transform infrared spectroscopy were employed for rheological and chemical analysis. Results indicated that extended exposure to thermal conditioning and UV irradiation had the most impact on the chemo-rheological properties of the binders. The incorporation of CR into bitumen enhanced ageing resistance and mitigated the potential for stiffening and embrittlement. The addition of GFA, PCP, and CB to CRMB had a negligible impact on the chemo-rheological properties when subjected to RTFO, PAV, and thermal conditioning. However, following UV ageing, these additives led to a slight increase in carbonyl bonds and greater stiffness compared to pure CRMB

Mechanical Properties and Microstructure of Laser Powder Bed Fusion‐Processed 18Ni300 Maraging Steel According to Direct Aging Treatment Conditions

The nonequilibrium microstructures produced by laser‐based additive manufacturing can enhance the mechanical properties of metallic alloys. However, the optimal post‐treatment conditions will change according to the initial microstructure induced by the manufacturing process employed. Therefore, this study investigates the optimal direct aging conditions for the post‐treatment of laser powder bed fusion‐processed 18Ni300 maraging steel by changing the aging temperature and time. The aging time required to achieve maximum tensile strength decreased as the aging temperature increased, and an increase in the aging temperature accelerated the evolution of nanoscale precipitates. The results indicate that the optimal direct aging conditions of 520 °C for 2 h achieved the largest tensile strength (≈2100 MPa) and precipitate area fraction. Notably, the reduced aging time at this temperature compared with that under conventional aging conditions (8 h at 460 °C or 490 °C) minimizes the thickening of the (Mo,Ti)‐rich segregation, which otherwise contributes to austenite reversion and strength reduction owing to overaging. Thus, the optimal direct aging conditions for additively manufactured maraging steel components are different from those for conventionally produced maraging steel components. This understanding of the microstructural changes induced by direct aging according to the initial non‐equilibrium state provides vital information for enhancing the performance of additively manufactured metallic alloys.

Evaluation of Seed Quality of Grain Corn Varieties through Accelerated Ageing

In an accelerated ageing test carried out to evaluate seed quality two hybrid grain corn varieties, 4546 and 888, were subjected to ageing conditions to assess their tolerance. The objective was to identify any differences between the varieties in their ability to maintain seed quality under accelerated ageing conditions. These tests simulate and hasten the natural ageing process of seeds, providing insight into their performance during storage over time and under adverse conditions. Following the ageing process, factors such as germination rate, vigour, and overall seed quality were assessed. The seeds of hybrid grain corn varieties 4546 and 888 were exposed to accelerated ageing by maintaining them at 40°C and 100% relative humidity in a growth chamber. Evaluations were conducted at intervals of 0, 48, 96, and 144 hours. The overall results indicated that seed quality in grain corn deteriorates following accelerated ageing treatment. Variety 4546 showed a rapid decrease in germination, germination rate, and seedling vigour throughout the testing period. Both varieties experienced an increase in moisture content from 11% to 20% during the ageing process. Additionally, the electrical conductivity of seed leachate increased for both varieties as the testing progressed. The experiment concluded that the 888 grain corn variety outperformed 4546 in all evaluated parameters. The 4546 variety was found to be highly sensitive to accelerated ageing.

Analysis of Ni-Cu Interaction in Aluminum-Based Alloys: Hardness, Tensile and Precipitation Behavior.

The present work was aimed at quantifying the effects of Ni addition in the range of 0-4% together with 0.3%Zr on the hardness and the tensile properties, volume fraction of intermetallics, and changes in size and distribution of phase precipitation in Sr-modified Al-9%Si-2%Cu-0.6%Mg cast alloys. The study was mainly carried out using high-resolution FESEM and TEM microscopes equipped with EDS facilities. Samples were solidified at the rate of ~3 °C/s and examined at different aging conditions. The investigations are supported by thermal analysis carried out at a solidification rate of ~0.8 °C/s. The results revealed that the main compositions of the Ni-based phases are close to Al3(Ni,Cu), Al3CuNi, and Al3Ni. An Al3Ni2Cu2 phase was also detected in the 4%Ni alloy. The Cu-Ni phases were observed to precipitate, covering the surfaces of pre-existing primary Al3Zr particles. The TEM analysis indicated the magnitude of the reduction in both size and density of the precipitated Al2Cu phase particles as the Ni content reached 4%, coupled with a delay in the transition from coherent to incoherency of the Al2Cu precipitates.

Numerical Investigation of Fracture Behaviour of Polyurethane Adhesives under the Influence of Moisture.

The mechanical behaviour of polymer adhesives is influenced by the environmental conditions leading to ageing and affecting the integrity of the material. The polymer adhesives have hygroscopic behaviour and tend to absorb moisture from the environment, causing the material to swell without applying external load. The focus of the work is to investigate the viscoelastic material behaviour under ageing conditions. The constitutive equations and the governing equations to numerically investigate the fracture in swollen viscoelastic material are discussed to describe the numerical implementation. Phase-field damage modelling has been used in numerical studies of ductile and brittle materials for a long time. The finite-strain phase-field damage model is used to investigate the fracture behaviour in aged viscoelastic polymer adhesives. The finite-strain viscoelastic model is formulated based on the continuum rheological model by combining spring and Maxwell elements in parallel. Commercially available post-cured crosslinked polyurethane adhesives are used in the current investigation. Post-cured samples of crosslinked polyurethane adhesives are prepared for different humidity conditions under isothermal conditions. These aged samples are used to perform tensile and tear tests and the test data are used to identify the material parameters from the curve fitting process. The experiment and simulation are compared to relate the findings and are the first step forward to improve the method to model crosslinked polymers.