Artificial Aging Conditions Research Articles

Mechanical characterization and structural analysis of elastodontic appliances under intraoral and artificial aging conditions

BackgroundThis study focused on the aging mechanism and degradation of mechanical and structural features of elastodontic appliances (EA) under artificial and intraoral aging to achieve oral myofunctional therapy with particular removable silicone elastomer devices.Materials and methodsEAs artificially aged in saliva with different pH values were investigated through cyclic compression testing along with characterization techniques (Scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy), and characterization analysis was also performed on clinically retrieved EAs.ResultsArtificial aging was found to have minimal effect on the structural properties of EAs, and intraorally aged samples showed perceptible micro-morphology. The Mullins index and peak stress decreased (P<0.01), while the compression set increased with prolonged aging time. Samples in alkaline saliva showed the largest Mullins effect (P<0.05).ConclusionsThe aging mechanism of the elastomer was found to be the crosslinking of main chains and scission of side chains. The presence of OH- enhanced the rupture degree of side bonds. The decline in viscoelastic properties was shown to be more severe with longer service durations.Clinical relevanceResearch on how the salivary environment and pH affect the aging characteristics of EAs is vital for guiding clinical applications and future modifications to extend their clinical lifetime.

Direct aging treatment of TiN modified Al–Mn–Sc alloy processed by laser powder bed fusion: On the microstructure evolution and mechanical property enhancement

In this study, the TiN nanoparticles modified Al–Mn-Sc composite and Al–Mn-Sc alloy have been fabricated by the laser powder bed fusion (LPBF). The microstructure, mechanical properties and strengthening mechanisms of these materials were discussed in details for both the as-built and artificial aged conditions. The results showed that the aged Al–Mn-Sc/TiN composite exhibits homogeneous nucleation with equiaxed grains ranging from 0.81 μm to 1.30 μm. After direct aging treatment of 300 °C, there are a volume fraction of secondary L12-Al3(Ti, Sc, Zr) nanoparticles precipitated in the composite sample, contributing to an ultra-high fracture strength of 701 ± 16 MPa. The increment in strength brought by TiN mainly comes from fine grains and high volume fraction of L12-Al3(Ti, Sc, Zr) nanoprecipitates. The fracture behaviors suggest that the uniform distribution of reinforced particles and less amount of micro pores can improve the strength and ductility of LPBF particle reinforced aluminum matrix composites.

The degradation of poly(1-butene) extrudates subjected to artificial and natural aging

In this work, we examined the degradation behavior of isotactic poly(1-butene) (PB-1) under artificial aging and natural weathering conditions. PB-1 samples underwent accelerated aging through UV irradiation and natural weathering. Chemical and structural changes in the degraded samples were characterized using Fourier-transform infrared–attenuated total reflectance (FTIR–ATR) spectroscopy, surface analysis, and wide-angle X-ray scattering (WAXS). The mechanical properties were evaluated via tensile testing. FTIR–ATR analysis revealed the presence of carbonyl groups in the degraded samples, indicating oxidative degradation. Surface observations employing scanning electron microscopy (SEM) revealed the formation of surface cracks in both samples, with differing crack initiation mechanisms. The two aging methods affected the mechanical properties of the samples: artificial aging induced a gradual reduction in both tensile modulus and strength, whereas natural weathering engendered a marginal increment in modulus alongside diminished strength. Additionally, elongation-at-break value witnessed a marked decrease in both sample sets during the preliminary stages of degradation. This work employed accelerated time equivalent, obtained by juxtaposition of the values of carbonyl index during both artificial aging and natural weathering and their interpolation to determine the degradation rate and adequately to correlate the final properties of the aged PB-1. It was observed that surface morphology and mechanical attributes of degraded samples were subject to additional influences such as temperature, humidity, and precipitation during natural weathering. This research work provided significant insights into PB-1 degradation mechanisms and effect of different aging conditions on its performance.Graphical abstract

Comparative Analysis of the Color Stability of Machined Denture Base Materials: An In-Vitro Approach.

Color stability is a crucial aspect in the selection of denture base materials as it directly impacts the esthetic appeal and longevity of dental prostheses. This study aimed to compare the color stability of different denture base materials through an in vitro approach. Three machined denture base materials including polymethyl methacrylate (PMMA), Acetal (AC), and polyether ether ketone (PEEK) were subjected to artificial aging using a xenon-arc lamp. Color measurements were taken before and after aging using a spectrophotometer. Statistical analysis was performed to determine any significant differences among the materials. The color stability of the denture base materials was quantitatively assessed using parameters such as ΔE values. PEEK exhibited the least color change (ΔE = 2.1 ± 0.3), followed by AC (ΔE = 3.5 ± 0.4), while PMMA showed the highest color change (ΔE = 5.9 ± 0.7). In this in vitro study, PEEK demonstrated superior color stability compared to AC and PMMA denture base materials under artificial aging conditions. These findings emphasize the importance of material selection in achieving long-term esthetic outcomes in dental prostheses.

Effect of Artificial Aging on Translucency of Zirconia Reinforced Lithium Silicate and Lithium Disilicate Ceramics: A Systematic Review.

Digital dentistry and advanced ceramic materials have been widely used but which material has a better esthetically durable outcome needs to be evaluated. The purpose of this systematic review and meta-analysis was to evaluate the difference in the translucency of CAD zirconia-reinforced lithium silicate and CAD lithium disilicate glass ceramics after being subjected to artificial aging. Two independent reviewers searched the MEDLINE/ PubMed, Embase, and EBSCO databases and the Google Scholar search engine for in-vitro studies published from January 2010 to May 2023 to identify relevant studies measuring the translucency of CAD ZLS and CAD lithium disilicate glass ceramics after being subjected to different artificial aging conditions using the coffee solution, 4% acetic acid, distilled water and UV aging. For qualitative synthesis, 10 studies were included. A statistically significant difference was observed between CAD zirconia-reinforced lithium silicate and CAD lithium disilicate glass ceramics (P⟨0.05, mean difference=-0.25 [-0.38,-0.11]). Translucency of CAD ZLS was less than CAD lithium disilicate glass ceramics. Artificial aging has decreased the translucency of glass ceramics. For fixed prosthetic rehabilitation clinicians can opt for CAD lithium disilicate glass-ceramic as a more esthetically pleasing and durable material in oral environment.

Non-destructive Near-infrared Hyperspectral Imaging in Food Technologies with a Focus on Monitoring Seed Viability

Seed qualities including viability and germination significantly influence the quantity and the quality of harvest. Technological means to assess seed qualities and attributes of seed-derived food products are varied. This paper highlights the use of infrared hyperspectral imaging (NIR- HSI) in food quality control, authentication, safety, process monitoring, shelf-life prediction, ingredients analysis, allergens detection and food sorting and grading. It also shows a particular application of NIR-HSI for the monitoring of nutrient content of sprouts and germinated seeds for industrial processing of foods with high nutritional values. The paper further reviews the applications of NIR-HSI to predict seed viability and germination. The non-destructive, rapid, and high-throughput capability of NIR-HSI were demonstrated through research works combining the NIR-HSI technology with chemometrics tools to reach more than 90% prediction rate. These relatively high rates may depend on the storage conditions or the stringency of the artificial aging conditions applied to parts of the seeds. However, the NIR-HSI has also proven efficient using naturally aged seeds with the prediction rates up to 90% correct classification, demonstrating the high capability of the technology. In combination with advanced chemometrics tools, some components of emerging technologies such as traditional machine learning and deep learning models have been added to increase the efficiency of NIR_HSI. Overall, the research works reviewed in this paper and which cover several food crops and food products showed that NIR-HSI is set to reach new heights in monitoring seed viability for improved seed stock management, crop production and innovation in the food industry.

Investigation on the Durability of a Polypropylene Geotextile under Artificial Aging Scenarios

Geosynthetics are widely used in various civil engineering applications, such as geotextiles in coastal protection, and display a sustainable alternative to natural mineral materials. However, the full benefits of using geosynthetics can only be gained with a long service lifetime of the products. With the use of added stabilizers to the polymers, service lifetimes can be achieved in the range of 100 years. Therefore, accelerated aging methods are needed for the assessment of the long-term performance of geotextiles. In the present study, the behavior of geosynthetic materials made of polypropylene was investigated under artificial aging conditions involving elevated temperatures ranging from 30 to 80 °C, increased oxygen pressures ranging from 10 to 50 bar in water-filled autoclaves, and UV irradiation under atmospheric conditions. ATR-IR spectroscopy was employed to detect the increase in the carbonyl index over various aging durations, indicating the oxidative degradation of the geotextile. The most pronounced increase was observed in the case of aging through UV irradiation, followed by thermal aging. Elevated pressure, on the other hand, had a lower impact on oxidation. High-temperature size exclusion chromatography was utilized to follow the reduction in molar mass under different degradation conditions, and the results were consistent with those obtained from ATR-IR spectroscopy. In polyolefins such as polypropylene, Hindered Amine Stabilizers (HAS) are used to suppress oxidation caused by UV radiation. The quantitative analysis of HAS was carried out using a UV/Vis method and HPLC. The degradation of UV stabilizers during the aging of geotextiles is responsible for the oxidation and the reduction in the molar mass of polypropylene. From the results, it can be concluded that applications of PP geotextile without soil or sand cover might cause the risk of the formation of microplastic particles. Material selection, design, and maintenance of the construction must follow best practices, including the system’s removal or replacement at end-of-life. Otherwise, a sustainable use of geotextiles in civil engineering is not possible.

Artificial aging conditions for Artemisia argyi leaves based on quality-inflammation-quality marker transformation

BackgroundAppropriate conditions for storage of Artemisia argyi leaves reduce irritation during treatment and increase the active ingredient content. Naturally aged A. argyi leaves (≥1 year) are optimal for moxibustion; however, this process is time-consuming and costly. A comprehensive understanding of the conditions for artificial aging of A. argyi leaves and the mechanism of quality-marker conversion are required to guarantee A. argyi quality and moxibustion efficacy. ObjectiveTo identify the optimal conditions for artificial aging of A. argyi leaves and clarify the mechanism of quality-marker conversion. MethodGas chromatography (GC), high-performance liquid chromatography (HPLC), colorimeter (CD), and near-infrared spectroscopy (NIRS) were used to determine the chemical composition of A. argyi leaves before and after artificial and natural (1 year) aging and to determine the optimal artificial aging conditions. The effects of both artificially and naturally aged A. argyi leaves were then evaluated in a mouse model of ulcerative colitis (UC). The main chemical components of aged A. argyi leaves were then analyzed to determine quality-markers and the transformation mechanism. ResultsComprehensive analysis of volatile and non-volatile components, color values, and characteristic near-infrared spectra revealed that the quality of artificially aged A. argyi leaves was similar to that of naturally aged A. argyi leaves. In the mouse model, artificially and naturally aged A. argyi leaves not only improved the symptoms of UC with the same therapeutic effects, but also safeguarded the barrier of the colonic mucosa and prevented the release of colitis-related substances. In addition, the content of caffeic acid converted from L-phenylalanine in A. argyi leaves increased during the aging process. ConclusionConditions for artificial aging of A. argyi leaves were identified for the first time, and the equivalent efficacy of artificially aged A. argyi leaves and naturally aged A. argyi leaves for improving UC was confirmed. This method for artificial aging of A. argyi leaves not only reduces the time and cost associated with this process, but also provides technical support to ensure the quality and stability of artificially aged A. argyi leaves. In addition, caffeic acid was identified as a potential quality-marker for establishing standards and specifications for aging A. argyi leaves for the first time, and its possible transformation mechanism was preliminarily elucidated.

Transcriptomic Profiling of Two Rice Thermo-Sensitive Genic Male Sterile Lines with Contrasting Seed Storability after Artificial Accelerated Aging Treatment.

Seed storability has a significant impact on seed vitality and is a crucial genetic factor in maintaining seed value during storage. In this study, RNA sequencing was used to analyze the seed transcriptomes of two rice thermo-sensitive genic male sterile (TGMS) lines, S1146S (storage-tolerant) and SD26S (storage-susceptible), with 0 and 7 days of artificial accelerated aging treatment. In total, 2658 and 1523 differentially expressed genes (DEGs) were identified in S1146S and SD26S, respectively. Among these DEGs, 729 (G1) exhibited similar regulation patterns in both lines, while 1924 DEGs (G2) were specific to S1146S, 789 DEGs (G3) were specific to SD26S, and 5 DEGs (G4) were specific to contrary differential expression levels. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed that "translation", "ribosome", "oxidative phosphorylation", "ATP-dependent activity", "intracellular protein transport", and "regulation of DNA-templated transcription" were significantly enriched during seed aging. Several genes, like Os01g0971400, Os01g0937200, Os03g0276500, Os05g0328632, and Os07g0214300, associated with seed storability were identified in G4. Core genes Os03g0100100 (OsPMEI12), Os03g0320900 (V2), Os02g0494000, Os02g0152800, and Os03g0710500 (OsBiP2) were identified in protein-protein interaction (PPI) networks. Seed vitality genes, MKKK62 (Os01g0699600), OsFbx352 (Os10g0127900), FSE6 (Os05g0540000), and RAmy3E (Os08g0473600), related to seed storability were identified. Overall, these results provide novel perspectives for studying the molecular response and related genes of different-storability rice TGMS lines under artificial aging conditions. They also provide new ideas for studying the storability of hybrid rice.

Comparative assessment of onion seed longevity under ambient storage and artificial ageing conditions

A study was carried out to assess the storage potential of onion genotypes under natural as well as accelerated ageing conditions. Freshly harveted seeds of thirty onion genotypes were subjected to nine months of natural ageing as well as accelerated ageing for 3 and 6 days (42oC and 75% RH). Significant effects of seed ageing on germination percent, seed vigour index, mean germination time and germination index were recorded. Germination percent ranged from 56.0- 96.0 percent in unaged seeds, which declined to 31.0-82.0 and 18.0-83.0 percent respectively after natural (9 months) and accelerated ageing treatments (6 days). In the current study, the seed germination and vigour indices decreased significantly, whereas the mean germination time increased for all the genotypes under both ageing treatments. Further, cluster analysis was utilized to categorize the onion genotypes into good or poorer storers. A significant and positive correlation was found among both natural as well as artificial ageing treatments. The study facilitated the categorization of onion genotypes into distinct storage groups by evaluating their performance under both natural as well as accelerated ageing.

Effect of mechanical properties, microstructure and residual stress on the bending springback behavior of high-strength Al–Mg–Si–Cu alloy tubes

In this work, the bending behavior of high-strength Al–Mg–Si–Cu alloys and AA6061 under different artificial aging condition was investigated. The existing springback prediction formula is suitable for commercial AA6061 alloy, but not for high-strength Al–Mg–Si–Cu alloy. Subsequently, the microstructure, mechanical properties and residual stress of AA6061 and high-strength Al– Mg–Si–Cu alloys were investigated. The results show that the yield strength and residual stress play important roles on the springback of high-strength Al–Mg–Si–Cu alloy. In addition, a springback prediction formula based on residual tensile stress has been proposed, which makes the prediction accuracy higher than 96 %. This provides theoretical guidance and data support for the application of high-strength Al–Mg–Si–Cu alloys in lightweight automotive materials.

Electron microscopic investigation of precipitation hardening in Al-Si based alloys

The present work was performed on Al-8.5%Si-1.75%Cu-0.55%Mg-0.2%Ti-0.32%Zr-0.015%Sr alloy (coded as 354 alloy) following T6 (at 160 °C) and T7 (at 240 °C) artificial aging conditions using high resolution transmission electron microscopy (HR-TEM). The main results inferred from the present study are the precipitation of GP zones in samples aged for 20 h at 160 °C along with S-Al2CuMg phase particles. Aging at 240 °C was carried out for different times, ranging between 30 min and 200 h. The quenched structures revealed a series of precipitations mainly GP zones at low aging times to Θ’-Al2Cu after 200 h together with the S-phase. No coherency was observed between the S-phase and the aluminum (Al) matrix. The growth of the S- phase takes place by precipitation of S2 type phase on the advancing S1-type phase. Mismatching was clearly observed at particle/matrix interfaces. High magnification images indicated the dissolution of some of the Θ” and Θ’ particles to enrich the nearby particles (coarsening). The start of incoherency is observed when the alloy is aged at 240 °C for 200 h.

On anisotropic tensile mechanical behavior of Al–Cu–Li AA2198 alloy under different ageing conditions

The anisotropic mechanical behavior of Al–Cu–Li (AA2198) alloy under different artificial ageing conditions as well as for different thicknesses of the material was examined in the present investigation. Material characterization was performed for three different sheet directions, namely, longitudinal (0°), diagonal (45°) and transverse (90°) to the rolling direction. The results showed that the grain structure did not have significant changes by applying different artificial ageing times. In T3 heat treatment condition, only δ′ (Al3Li) phase was observed, while with increasing the ageing time, the major precipitates were T1 (Al2CuLi) phases. The latter was found to increase in size with artificial aging time. Almost similar yield strength values were observed for all investigated thicknesses, while the higher thickness specimens showed higher elongation at fracture values. Anisotropy was slightly higher at T3 condition, while the lowest anisotropy degree was noticed at the peak-aged condition. The specimens extracted in the diagonal direction showed high variation in mechanical properties, when compared with the respective results at the other two investigated directions, independently from the thickness of the specimens as well as from heat treatment condition. The smaller thickness specimens presented lower elongation at fracture values and for all investigated sheet directions, since they undergo plane stress conditions. Analysis of work hardening behavior showed that Bauschinger effect, which was not observed in T3 condition, became increasingly more prominent with artificial ageing time in all directions investigated.

Effect of trace Zn addition on microstructure and corrosion behavior of AA2024 under different aging treatments

The effect of trace Zn (0.67 wt%) addition on the microstructure and corrosion behavior of AA2024 under different aging treatments was investigated. The results reveal that, with trace Zn addition, the corrosion depth decreases at the natural aging condition, but increases at the artificial aging treatment (both the peak aging condition and over aging condition). The corrosion morphology of the Zn-containing alloy under different aging treatments is also different from that of the Zn-free alloy. Compared with the Zn-free alloy, the dealloying process of the S phase in the Zn-containing alloy is slower, which are not conducive to the formation of pitting corrosion. Transmission electron microscope shows that trace Zn addition can promote the nucleation of the intragranular Guinier-Preston-Bagaryatski zones which transform into S phases in the subsequent aging process. Compared with the Zn-free alloy, the S phases of the Zn-containing alloy are coarser at the over aging condition. Moreover, details of how the corrosion morphology of Zn-containing alloys changed and the relationship between the microstructure and the corrosion behavior were discussed. • Trace Zn inhibits the dealloying of Intermetallic S particles. • The local corrosion depth at the natural aging condition is small and the local corrosion depth at the artificial aging condition is large in the AA2024 with trace Zn compared with the Zn free alloy. • Zn segregated at the S-Al interface has been characterized. • Trace Zn promotes the growth and coarsening of grain boundary S phase particles in the AA2024 under artificial aging treatments. • Zn promotes the coarsening of S phase at the grain boundary and the aggregation of Zn at the S-Al interface works together on the local corrosion morphology of the alloy.

Dependency of mechanical properties on artificial aging conditions for EN AW 6082 aluminum alloy

Aluminum 6xxx series alloys attract attention owing to their decent strength, formability and corrosion characteristics. Mechanical properties of these alloys can be altered via precipitation hardening by applying an aging treatment known as artificial aging (AA). This investigation was focused on the behavior of mechanical properties of EN AW 6082 alloy for various aging conditions. Mechanical property response for different heat treatment procedures were analyzed together with DSC results and TEM micrographs. Solution heat treatment (SHT) temperature was found to affect the obtained yield strengths after AA considerably and higher SHT temperatures lead to higher yield strength for same artificial aging condition. It was also shown that yield strength values obtained after 480 min—180 °C artificial aging can be surpassed in shorter times at higher artificial aging temperatures. Aging times as short as 60 min may be employed using temperatures above 200 °C to obtain higher strength than 480 min—180 °C aging. Linear relationships between Vickers hardness and mechanical strengths were suggested for the complete data of the study. Negative effects of over-aging on ductility were presented and β′′ precipitates which are responsible for hardening during aging were presented using TEM micrographs. Additionally, high cycle fatigue tests were conducted for AA procedures 480 min—180 °C and 240 min—200 °C and similar fatigue strengths were reported.

Non-destructive Evaluation of Workpiece Properties along the Hybrid Bearing Bushing Process Chain

To combine the advantages of two materials, hybrid bulk metal workpieces are attractive for subsequent processes such as metal forming. However, hybrid materials rely on the initial bond strength for the effective transfer of applied loads. Thus, a non-destructive evaluation of the bonding along the production process chain is of high interest. To evaluate to what extent non-destructive testing can be employed to monitor the bonding quality between the joining partners steel and aluminum and to characterize the age hardening condition of the aluminum component, ultrasonic testing and electrical conductivity measurements were applied. It was found that a lateral angular co-extrusion process can create homogeneous bonding although the electrical conductivity of the aluminum is altered during processing. A previous bonding before the subsequent die forging process leads to a sufficient bonding in areas with little deformation and is therefore, advantageous compared to unjoined semi-finished products, which do not form a bonding if the deformation ratio is too small. An influence of the subsequent heat treatment on the bonding is not visible in the ultrasonic testing signals though a homogenized electrical conductivity can be detected, which indicates uniform artificial aging conditions of the aluminum alloy

Assessing Seedbank Longevity and Seed Persistence of the Invasive Tussock Grass Nassella trichotoma Using in-Field Burial and Laboratory-Controlled Ageing

The ability to produce highly dense and persistent seedbanks is a major contributor to the successful widespread establishment of invasive plants. This study seeks to identify seed persistence and seedbank longevity for the invasive tussock grass Nassella trichotoma (Nees.) Hack. ex Arechav in order to recommend management strategies for preventing re-emergence from the seedbank. To determine the seedbank longevity and persistence, two experiments were conducted: (i) seeds were buried at four depths (0, 1, 2, and 4 cm) and collected and assessed for viability, seed decay, and in-field germination after 6, 9, 12, 15, and 18 months of field burial; and (ii) seeds were exposed to artificial ageing conditions (60% RH and 45 °C) for 1, 2, 5, 9, 20, 30, 50, 75, 100, and 120 days, and viability was determined through germination tests and tetrazolium tests. Less than 10% of the seeds collected after 12 months of in-field burial were viable. The artificial ageing treatment found germination declined to 50% after 5.8 days, further suggesting that N. trichotoma seeds are short lived. The results from both experiments indicate that N. trichotoma has a transient seedbank, with less than 10% of the seeds demonstrating short-term persistence. It is likely the persistent seeds beyond 12 months were exhibiting secondary dormancy as viable seeds did not germinate under optimal germination conditions. The “Best Practice Guidelines” recommend monitoring for seedbank recruitment for at least three years after treating N. trichotoma infestations. The results of this study support this recommendation as a small proportion of the seeds demonstrated short-term persistence.

Microstructure and Mechanical Properties of an Al-Mg-Si-Zr Alloy Processed by L-PBF and Subsequent Heat Treatments.

The aim of this study was to develop a new Al–Mg–Si–Zr alloy with a high magnesium content to achieve a wide range of mechanical properties using heat treatment and at a lower cost. Additive manufacturing was conducted using a powder bed fusion process with various scan speeds to change the volumetric energy density and establish optimal process conditions. In addition, mechanical properties were evaluated using heat treatment under various conditions. The characterization of the microstructure was conducted by scanning electron microscopy with electron backscatter diffraction and transmission electron microscopy. The mechanical properties were determined by tensile tests. The as-built specimen showed a yield strength of 447.9 ± 3.6 MPa, a tensile strength of 493.4 ± 6.7 MPa, and an elongation of 9.6 ± 1.1%. Moreover, the mechanical properties could be adjusted according to various heat treatment conditions. Specifically, under the HT1 (low-temperature artificial aging) condition, the ultimate tensile strength increased to 503.2 ± 1.1 MPa, and under the HT2 (high-temperature artificial aging) condition, the yield strength increased to 467 ± 1.3 MPa. It was confirmed that the maximum elongation (14.3 ± 0.8%) was exhibited with the HT3 (soft annealing) heat treatment.

Experimental and numerical investigation of laser beam-welded Al–Cu–Li joints using micro-mechanical characteristics

The local tensile mechanical properties of laser beam-welded joints of AA2198 alloy with Al–Si filler wire were experimentally investigated. For this purpose, micro-flat tensile specimens were extracted from the fusion zone and the heat-affected zone. The chemical composition of the filler wire affects the local mechanical properties in the fusion zone, showing an approximately 26% decrease in yield strength from the radiation exposure side to the weld root side. The effect of post–weld heat treatment on the tensile mechanical behavior was additionally investigated for different heat treatment artificial ageing conditions. The maximum yield strength increase was noticed for 48 h of artificial ageing for the weld root side of the fusion zone. Several approximations were proposed to correlate the hardness measurements with the local tensile mechanical properties of the welded joint that allow for a fast assessment of the global tensile mechanical behaviour of the welded joint. To evaluate the effect of (i) artificial ageing and (ii) geometrical imperfections of the weld on the mechanical behavior of the welded joint, finite element analyses were performed, using the local mechanical properties as input to the model. It is shown that the local mechanical properties of the fusion zone play a pivotal role on the strain localization and fracture of the welded joint.

Fabric-Reinforced Cementitious Matrix (FRCM) Carbon Yarns with Different Surface Treatments Embedded in a Cementitious Mortar: Mechanical and Durability Studies.

Nowadays, FRCM systems are increasingly used for the strengthening and retrofitting of existing masonry and reinforced concrete structures. Their effectiveness strongly depends on the bond that develops at the interface between multifilament yarns, which constitute the reinforcing fabric, and the inorganic matrix. It is well known that fabric yarns, especially when constituted by dry carbon fibers, have poor chemical-physical compatibility with inorganic matrices. For this reason, many efforts are being concentrated on trying to improve the interface compatibility by using different surface treatments on multifilament yarns. In this paper, three different surface treatments have been considered. The first two involve yarn pre-impregnation with flexible epoxy resin or nano-silica coating, while the third one involves a fiber oxidation process. Uniaxial tensile tests were carried out on single carbon yarns to evaluate tensile strength, elastic modulus and ultimate strain before and after surface treatments, and also after yarn exposure to accelerated artificial aging conditions (1000 h in saline or alkaline solutions at 40 °C), to evaluate their long-term behavior in aggressive environments. Pull-out tests on single carbon yarns embedded in a cementitious mortar were also carried out, under normal environmental conditions and after artificial exposure. Epoxy proved to be the most effective treatment, by increasing the yarn tensile strength of 34% and the pull-out load of 138%, followed by nano-silica (+9%; +40%). All surface treatments were shown to remain effective even after artificial environmental exposures, with a maximum reduction of yarn tensile strength of about 13%.