Cylindrical Specimens Research Articles

Evaluation of the behavior of the interface zone between an asphalt mixture and an inductive power transfer pad

Wireless charging of Electric Vehicles (EVs) is seen as part of an important strategy to reduce emissions from essential transportation trips of people and goods. Resonant Inductive Power Transfer (IPT) is used in the development of wireless charging systems for in-road charging systems. IPT pads are embedded in a pavement infrastructure to create a magnetic field that is coupled into a similar pad fitted underneath an EV. This is then converted to the voltage and current needed to charge the onboard battery. This method enables EVs to wirelessly receive a charge while stationary or in motion. However, ensuring the robustness of this integrated in-road system is essential. Poor interface bonding between a surrounding asphalt mixture and an IPT pad decreases the structural integrity within the IPT pad-asphalt pavement system, hence increasing the risk of damage to the system. The purpose of this study is to investigate the behavior of an IPT pad-asphalt interface zone by performing direct shear tests. In the experimental setup, a normal compressive load is applied to a three-layer cylindrical specimen, comprising an asphalt mixture, the interface material, and the material forming the outer containment layer of the pad. The influence of temperature, moisture, and normal stress on the interface shear strength is investigated. Among the three interface materials tested (epoxy bitumen, epoxy resin, and structural plastic adhesive), the epoxy resin material showed the highest shear strength at 25 °C. The interface shear strength and the shear stiffness decreased for all three materials with increasing temperature, with the epoxy bitumen material being the most temperature sensitive, yielding a decrease in strength of 77 % and stiffness of 62 % between 15 °C and 40 °C. Experiments were performed using an orthogonal test design. Five variables, known to affect the interface shear strength, each variable assuming three values, were considered. The results of a range analysis and analysis of variance (ANOVA) showed that temperature has the most significant effect on the shear strength of the interface zone, i.e. between the asphalt mixture and pad surfacing. Other important factors affecting the shear strength are the interface material and the shear deformation rate. A numerical study of a full-scale IPT-asphalt pavement system is presented to show the effect of the interface bonding condition on the longitudinal and transverse strains at the bottom of the asphalt layer and the fatigue life. The results of this study will be used in the design of an IPT pad-asphalt pavement system by minimizing the differential permanent displacements between an IPT pad and the surrounding asphalt pavement.

Study on the Effect of OPC and PCC on the Properties of Concrete

The objective of the study was to evaluate the effect of OPC and PCC on the compressive and tensile strength of concrete with age. Accordingly, cylindrical specimen was prepared by using cement OPC and PCC. Incasting the specimen only crushed bricks are used as coarse aggregate and Sylhet sand (FM=2.65) has been used as fine aggregate. Two different water cement ratios is 0.45, 0.60 and mix ratio 1:1.5:3 and 1:2:4 (by volume) has been adopted. Concrete cylinder made with OPC show higher compressive and tensile strength at 28 days then the those made with PCC. However, it has been from that Concrete made with OPC gains compressive strength at (45 days) a faster rate up to a certain age of concrete. While concrete with PCC attains larger strength at later age. In this study, it has been found that up to 45 days, the attained compressive strength of OPC concrete is larger than PCC concrete. However, the observed compressive strength beyond 60days is larger than OPC concrete. Similar trend has been observed in the case of tensile strength.

Constitutive response and failure progression in digitally fabricated (3D printed) concrete under compression and their dependence on print layer height

Among the several geometry and process-related characteristics that determine the ultimate product quality of 3D printed concrete, one that has gained considerable importance is the height/thickness of the individual layers. Layer height dictates the number of interlayer interfaces, and influences the properties of the layer and the interfaces (both interlayer and inter-filament), for a given mixture and printer characteristics. This paper examines the influence of layer height on the constitutive response and failure of 3D printed concrete specimens under compression, investigated along the direction of layer build-up (or perpendicular to the layer interfaces), which is the dominant plane of loading in 3D printed walls and columns. Plain and steel fiber-reinforced wall elements with two different layer heights (7.5 mm and 15 mm) are printed, from which cylindrical and prismatic specimens are extracted and tested. The uniaxial compressive strength is seen to decrease with increasing layer height. The constitutive relationships of the specimens with different layer heights, along with volumetric strains, enable the extraction of crack initiation stress and unstable crack propagation stress, which are influenced by layer height and the presence of fiber reinforcement. The unstable crack propagation stress is lower than the peak stress, and it decreases with increasing layer height. Digital image correlation (DIC) is used to demonstrate the dominant effect of inter-filament interfaces on the crack propagation response and resultant failure.

Analisis Penambahan Serbuk Kayu Sebagai Kayu Sebagai Pengganti Terhadap Agregat Halus

This study aims to analyze the impact of adding sawdust as a substitute for fine aggregate in concrete mixes, with percentage variations of 1%, 1.5%, and 2%. The experiments involved the preparation of concrete mixtures with specific proportions according to each sawdust variation, and the formation of cylindrical concrete samples with a size of 15 cm x 30 cm. A total of 12 cylindrical specimens were prepared for each variation, ensuring representativeness and reliability of the results. Subsequently, mechanical properties of the concrete were tested, including compressive strength, resistance to compressive load, and resistance to deformation. The expected compressive strength plan was 16.9 MPa, but the test results showed a decrease in concrete at 1% by 11.99 MPa, at 1.5% by 7.14 MPa, and at 2% by 5.65 MPa. Analysis of these results provides a focal point for planning strategies to improve the performance of concrete with sawdust and ensure that its use does not compromise critical compressive strength. The findings of this study are expected to provide guidance for the construction industry in integrating alternative, more environmentally friendly materials into daily construction practices.

A comparison of high strain rate response and adiabatic shear band formation in additively and traditionally manufactured Inconel 718

3D printing of Inconel 718 has been increasingly commercialized, as such research comparing the mechanical properties of additively manufactured (AM) and traditionally manufactured (TM) components in both quasi-static and high rate regimes should be conducted. Herein, the high strain rate material response, as well as the formation of adiabatic shear bands (ASBs) in AM and TM Inconel 718 are studied using a split Hopkinson pressure bar (SHPB) system. A top-hat cylindrical specimen geometry was used to convert the compressive load to shear and conduct high rate shear tests in the SHPB. The quasi-static and high rate stress-strain data reported herein indicates that TM components have at least a 70 MPa higher compressive yield strength. Interestingly, the AM specimens were more susceptible to ASB formation than their TM counterparts. The critical shear strain at which an ASB forms was higher for the TM specimens compared to the AM specimens. This was attributed to the TM material having a higher critical stress for dynamic recrystallization initiation, which is required to ASB formation. The microstructures of the shear zone in the top-hat specimens were examined using an optical microscope (OM), scanning electron microscope (SEM), and transmission electron microscope (TEM). Dynamic recrystallization was observed at the center of the shear affected zone (SAZ) using TEM from material lifted out from the ASB. Due to the plastic deformation in the shear region, the material strain hardens and therefore has a higher hardness than the bulk material. At the center of the shear region, a peak in nano-hardness of 585 HV was recorded on the ASB. The outcome of this research will lead to the prevention, containment, and control of shear instability in AM structures.

A Constitutive Model for Circular and Square Cross-Section Concrete Confined with Aramid FRP Laminates

Fiber-reinforced polymer (FRP) has been used for seismic retrofitting and structural reinforcement over recent decades. Numerous researchers have created stress–strain models based on experimental data to predict the mechanical properties of FRP-confined concrete. In this study, circular and square cross-section specimens with different design concrete strength were prepared, and the compressive strength of the specimens confined with different layers of aramid FRP (AFRP) were measured in compressive tests. A constitutive model was proposed to simulate the uniaxial compressive stress–strain relationship of the AFRP-confined concrete, which was derived from the Mohr–Coulomb failure envelope theory, and the corresponding axial strain was determined from the regression analysis. The internal friction angle of the proposed constitutive model was determined for the cylindrical concrete specimens confined with one and two layers of AFRP. The compressive strength of one and two layers of AFRP-confined concrete specimens were used to obtain the parameters of the constitutive model; the absolute average error between experimental and predicted compressive strength was 7.01%. Then, the constitutive model was used to predict the strength of a three-layer AFRP-confined concrete specimen, and the absolute average error was 4.95%. The cross-sectional shape coefficient of the square concrete specimen was obtained analytically. Substituting the cross-sectional shape coefficient into the proposed constitutive model, the average absolute error of the square cross-section concrete specimen was about 3.84%. The results indicated that the proposed constitutive model can predict the compressive strength of circular and square cross-section concrete specimens confined with AFRP.

Slag-modified metakaolin-based 3D printed geopolymer: Mechanical characterisation, microstructural properties, and nitrogen physisorption pore analysis

This study aims to enhance metakaolin (MK)-based binders with slag up to 30% at 10% intervals and increase the aggregate-to-binder ratio (a/b) from 1.6 in a previous study to 2 for extrusion-based 3D printed geopolymer concrete (3DPGPC). Sodium phosphate (3% by mass of binders) was used to tailor the fresh properties of the slag-modified MK-based 3DPGPC mixtures to achieve sufficient open time for constructability. After 28 days of curing age, cylindrical 3DPGPC specimens cored perpendicular to the printing direction (D1) exhibit an average compressive strength of 23.7–31.52 MPa and the specimens cored parallel to the printing direction (D3) exhibit an average compressive strength of 25.25–33.13 MPa. Also, an increase in a/b from 1.6 to 2 increases the average compressive strength by 18% in D1 and 25% in D3. The average flexural strength of specimens in D1 attained 5.48–7.29 MPa, while the average interlayer bond strength of 3DPGPC beam specimens attained 5.40–6.90 MPa. An increase in a/b from 1.6 to 2 enhanced average flexural strength by 6%. Furthermore, the 28-day splitting tensile strength of cored cylindrical 3DPGPC specimens attained 1.79–2.16 MPa in D1 and 2.04–2.43 MPa in D3. Microstructural characterisation revealed the formation of C-S-H, N-A-S-H and C-A-S-H gel with increasing slag inclusion due to the presence of Ca2+ion. Nitrogen physisorption analysis shows that the adsorption and desorption isotherm curves and hysteresis loops were not altered but more nitrogen by volume was absorbed due to the formation of a significant quantity of C-S-H, N-A-S-H and C-A-S-H gel. The adsorption and desorption isotherms fall under the mesopores structure of 2–50 nm using the IUPAC technical report classification. The Brunauer-Emmett-Teller (BET) surface area increases by 67, 69, and 78% as slag content increases by 10, 20 and 30% due to the polymerisation of the reactive phases, which densify the matrices. The enhanced mechanical performance, microstructural properties, and pore structure system of slag-modified MK-based 3DPGPC ascertained that it is suitable for construction applications.

Investigating icing behavior in cementitious material during freeze–thaw using low-temperature low-field NMR

Low-temperature low-field nuclear magnetic resonance was applied to analyze the icing amount in water saturated white cement paste specimens at different temperatures during the freeze–thaw process. An innovative cylindrical specimen shape eliminated temperature gradients and enabled real-time monitoring of icing. The experimental results were compared with the results obtained using classical theory, showing good agreement from 0 °C to −8 °C but notable differences from −8 °C to −18 °C. Therefore, experimental data from specimens saturated with pure water, a 4 % salt solution, and an 8 % salt solution were analyzed to obtain the freezing probability according to pore size classification, and new equations were proposed on this basis to relate the volume of frozen water to temperature during the freezing and thawing of cementitious materials.

Mechanical properties of simulated dentin caries treated with metal cations and L-ascorbic acid 2-phosphate.

This pH cycling study aimed to investigate the effects of L-Ascorbic acid 2-phosphate (AA2P) salts of Mg, Zn, Mn, Sr, and Ba on the surface microhardness, compressive strength, diametral tensile strength (DTS), and solubility of root canal dentin. 186 cylindrical dentin specimens from 93 teeth were fortified with optimal concentrations of AA2P salts of Mg (0.18mM), Zn (5.3µM), Mn (2.2 × 10-8M), Sr (1.8µM), and Ba (1.9µM). Saline was used as the control group. These dentin specimens underwent a 3-day cycling process simulating dentin caries formation through repeated sequences of demineralization and remineralization. Surface microhardness at 100 and 500µm depths (n = 10/subgroup), scanning electron microscopy (n = 3/group), compressive strength (n = 10/group), DTS (n = 6/group), and solubility (n = 5/group) tests were performed to analyze the dentin specimens. Data were analyzed using Kolmogorov-Smirnov, one-way ANOVA, and Post Hoc Tukey tests (p < 0.05). The control group had significantly lower microhardness at both depths (p < 0.001), reduced DTS (p = 0.001), decreased compressive strength (p < 0.001), and higher weight loss (p < 0.001) than all other groups. The Sr group had the highest compressive strength and microhardness among all the groups. The microhardness was significantly higher for the 500µm depth than the 100µm depth (p < 0.001), but the difference in microhardness between depths across groups was not significant (p = 0.211). All fortifying solutions provided some protection against artificial caries lesions. Therefore, these elements might have penetrated and reinforced the demineralized dentin against acid dissolution.

Compression Behavior and Textures of Ti57-Nb43 Alloy at High Temperatures.

The mechanical behavior, microstructures, as well as the crystallographic textures of the Ti57-Nb43 alloy were investigated on cylindrical specimens compressed at high temperatures, in the range of 700-1000 °C, and strain rates between 0.001 and 1.0 s-1. Hardening, followed by softening behaviors, were observed as a function of strain due to the occurrence of dynamic recrystallization/recovery in hot deformation. The modified five-parameter Voce-type equation described well the stress-strain curves, but, for the present alloy, it was also possible with only four parameters. A new two-variables polynomial function was employed on the four parameters that described well the flow curves as a direct function of temperature and strain rate. It permitted the reduction in the number of parameters and had the predictive capacity for the flow stress at any temperature, strain, and strain rate in the investigated range. The crystallographic textures were similar at all temperatures, with an increase in intensity from 900 °C. The textures could be characterized by a double <100> and <111> fiber and a unique component of (001) <110>, the latter inherited from the initial hot-rolling texture. Viscoplastic polycrystal self-consistent deformation modeling reproduced the measured textures showing that dynamic recrystallization did not alter the development of the deformation texture, only increased its intensity.

Fatigue enhancement and hardening effect through ultrasonic vibration‐assisted ball‐burnishing process on AISI 1045 steel

AbstractThis paper aims to present a study of the effects of ball burnishing with vibration assistance on the bending fatigue endurance of cylindrical specimens subjected to bending stress and obtain the best input parameters. The specimens were burnished through six different combinations of preload force, number of passes, and vibration assistance, finding that burnishing while applying a 90‐N preload, five passes, and the addition of vibration assistance results in larger fatigue strength. In terms of roughness, it has been proved that vibration‐assisted ball burnishing reduces the mean roughness up to 90%, while enhancing the skewness and kurtosis parameters. The softening effect while deforming, caused by the vibration assistance, helped to reconstruct the surface, obtaining higher depths of affectation and hardening. Fatigue strength was improved by a 6.54% by only adding vibration assistance to the ball‐burnishing process.

Experimental Study of the Effect of Different Insulation Schemes on Fire Performance of FRP Strengthened Concrete: FIRECOAT and REALROCK

The past two decades have witnessed rapid advances in the use of fiber-reinforced polymer (FRP) composites in different engineering fields. Advantages such as high strength-to-weight ratio, corrosion resistance, and tailority have led to immense interest in the use of FRPs in wide spectrum repair and strengthening of structures. Despite their many advantages, FRPs are highly sensitive to high temperatures, which pose a major concern for fire potential structures such as buildings. Applying proper thermal insulation can enhance the fire performance of FRP and reduce the possible fire damage to the FRP strengthened element. This study set out to experimentally investigate the effectiveness of two insulation systems, “FIRECOAT” and “REALROCK” on fire performance of CFRP and GFRP strengthened concrete specimens. Various configurations and exposure durations were considered to evaluate the effectiveness of insulating materials. To perform the experiments, cylindrical concrete specimens were fabricated and strengthened using CFRP or GFRP. After insulating the specimens, they were exposed to a standard fire curve for two different durations of 30 and 60 min. The results indicate that less than 30 min of fire, both insulation systems can provide the required protection. During long exposure duration of 60 min, only REALROCK can provide the required thermal resistance for FRP-strengthened concrete. Within the tested materials, Fire Set 60 outperformed other insulating materials. It was observed that implementing Fire Set 60 in the innermost layer of thermal insulations has crucial importance in preventing the fire induced reductions in strength of FRP-strengthened concrete elements.

Free vibration characteristics of integrated fluted-core composite sandwich cylinders

Due to their excellent mechanical properties and inherent design versatility, fluted-core composite sandwich structures have gained substantial attention in aerospace and rail transit applications. This study investigated the free-vibration characteristics of composite fluted-core sandwich cylinders. Theoretical models were established following the Rayleigh-Ritz method to predict the natural frequencies of sandwich cylinders under free vibration. The representative cylindrical specimens were prepared using carbon fiber-reinforced plastics (CFRP) and integrated forming co-cured method. To analyze the additional effects of cutouts on vibration performance, specimens with circular cutouts were also fabricated. The vibration tests were performed to determine the natural frequencies and modal shapes under free-free boundary conditions. Validated finite element simulations were employed to assess the accuracy of theoretical results and investigate the influences of geometric parameters on the structural vibration behavior. The results indicated that circumferential lobar modes characterized the first five mode shapes. Significant enhancements were attained by increasing the structural stiffness through adjustments in the circumferential cell number, core-ribs thickness, or size of cutouts. However, when the structural stiffness increases beyond a certain threshold, it has limited effect on the vibration frequencies. The findings provided a comprehensive understanding of the vibration characteristics and optimized design of fluted-core sandwich cylinders.

Explainable Data-Driven Ensemble Learning Models for the Mechanical Properties Prediction of Concrete Confined by Aramid Fiber-Reinforced Polymer Wraps Using Generative Adversarial Networks

The current study offers a data-driven methodology to predict the ultimate strain and compressive strength of concrete reinforced by aramid FRP wraps. An experimental database was collected from the literature, on which seven different machine learning (ML) models were trained. The diameter and length of the cylindrical specimens, the compressive strength of unconfined concrete, the thickness, elasticity modulus and ultimate tensile strength of the FRP wrap were used as the input features of the machine learning models, to predict the ultimate strength and strain of the specimens. The experimental dataset was further enhanced with synthetic data using the tabular generative adversarial network (TGAN) approach. The machine learning models’ performances were compared to the predictions of the existing strain capacity and compressive strength prediction equations for aramid FRP-confined concrete. The accuracy of the predictive models was measured using state-of-the-art statistical metrics such as the coefficient of determination, mean absolute error and root mean squared error. On average, the machine learning models were found to perform better than the available equations in the literature. In particular, the extra trees regressor, XGBoost and K-nearest neighbors algorithms performed significantly better than the remaining algorithms, with R2 scores greater than 0.98. Furthermore, the SHapley Additive exPlanations (SHAP) method and individual conditional expectation (ICE) plots were used to visualize the effects of various input parameters on the predicted ultimate strain and strength values. The unconfined compressive strength of concrete and the ultimate tensile strength of the FRP wrap were found to have the greatest impact on the machine learning model outputs.

Characterization of the temperature and frequency dependency of the complex Poisson’s ratio using a novel combined torsional-axial rheometer

This study discusses the feasibility of using a combined torsional-axial rheometer to indirectly measure the complex Poisson’s ratio based on shear and Young’s modulus. For this purpose, isothermal frequency sweeps in torsion and extension are performed sequentially on the same cylindrical specimen and under the same environmental conditions. The method is tested on two amorphous polymers, a semicrystalline polymer, a polymer blend, and a copolymer. The article includes an extensive literature review and an uncertainty assessment of the method to provide a basis for subsequent data comparison with existing research. The experimental data show a monotonic increase in the complex Poisson’s ratio up to 0.5 as the temperature approaches α-relaxation for all samples, except for the amorphous polymer. The latter shows a local minimum in the complex Poisson’s ratio observed near α-relaxation, which disappears after thermal annealing of the sample above the α-relaxation temperature. The real and imaginary parts of the complex Poisson’s ratio are additionally determined by evaluating both phase shift angles from torsional and extensional measurements. All polymers show a certain offset between the torsional and extensional phase shift angles in the glassy state, which gradually decreases as the temperature approaches α-relaxation. The complex Poisson’s ratio results are in good agreement with the literature data obtained by existing methods. This confirms that the method is applicable to polymers up to α-relaxation temperatures with significant time savings due to the nondestructive approach. This is of particular interest, given the limited availability of data in the literature.

Wave Velocities and Poisson Ratio in a Loose Sandy Martian Regolith Simulant Under Low Stresses: 1. Laboratory Investigation

AbstractWave velocity measurements were performed on Fontainebleau sand samples used as a Martian regolith simulant to investigate the elastic properties of the surface material at the InSight landing site on Mars (Elysium Planitia). Loose samples (density 1.4 Mg/m3, density index 6%) were prepared by using the pluviation method to mimic the low regolith density at the InSight landing site. A novel device derived from triaxial testing was designed to measure wave velocities at low stresses along a horizontal cylindrical specimen. Four tests were made, in which the confining stress was applied by applying a vacuum between 1 and 80 kPa. Wave velocities were measured by using bender elements under stresses as low as 1.75 kPa, a very low value compared to the standard stress ranges generally considered in terrestrial geotechnics (&gt;10 kPa). The changes in compression and shear wave velocities obey a standard power law, with two slightly different exponents for Vp and Vs, indicating a not perfectly elastic behavior. Data showed greater variability below 5 kPa, indicating some limitations of the bender element technique in this range. A slight decrease in Poisson ratio was detected below 5 kPa, which certainly deserves more investigation. This investigation is useful to better analyze the data of the InSight mission, both in terms of wave propagation at the surface and to interpret some in situ elastic tests carried out with the scoop. These data are interpreted in the light of a granular contact mechanics theory in a companion paper.

The Behaviour of Thin-Walled Cylinders with Reinforcing Inner Walls Subjected to High-Velocity Impact

Thin cylindrical tubes as impact energy absorbers have been widely used in various fields. Previous researchers have proposed many methods to increase the ability to absorb energy by modifying the geometry or using different materials. This study discusses using reinforcing walls in the cylinder to increase energy absorption capability. We make thin cylindrical specimens made of aluminium alloy with a length of 150 mm, a diameter of 50 mm, and a thickness of 1 mm. Reinforcing walls are fitted in the cylinder with a vertical position of 1, 2, 3, and without supporting walls. An impactor moving at high velocity hits the up-end cylinder in the axial direction. The finite element method modelling results show that installing reinforcing walls in thin-walled cylinders increase the maximum impact force, decreases the maximum deformation, changes the deformation mode, and increases the energy absorption capability. The amount of wall added to the thin wall will affect the impact behaviour of the specimen. However, in this study, the presence of a wall will have an effect when the deformation reaches the location of the wall. Nevertheless, using this reinforcing wall also makes the manufacturing process more complex. Therefore, this study’s results are recommendations for the design of the impact energy absorption structural system.

Increased Concrete Strength with the Addition of Hyacinth Natural Fibers

Concrete is a brittle and fragile construction material so it needs to be increased in strength. This study aims to increase the strength of concrete by adding natural fibers of water hyacinth to the concrete mixture. Hyacinth fibers are cut by 3-5 cm and added with variations of 0%, 0.1%, 0.2%, 0.3%, 0.4% and 0.5% of the volume of concrete. Cylindrical specimens 15 cm in diameter and 30 cm in height were tested for compressive strength and tensile strength at the age of 28 days. The test results showed that the addition of hyacinth fiber up to 0.5% increased the compressive strength of concrete up to 17.6% and tensile strength up to 71.4% compared to normal concrete without fiber. The increase in strength is due to hyacinth fibers being able to withstand micro-cracks in concrete. The more fiber added, the more microcracks are able to be prevented thereby increasing the strength of concrete. In conclusion, the natural fiber of hyacinth effectively increases the strength of concrete both in compressive and tensile capacity.

Effect of water environment on mechanical behavior of coral aggregate concrete

The complex marine environment often exposes concrete to seawater and acidic conditions during its service life. To investigate the effect and mechanism of special water environments on coral sand concrete, forty-five Φ50 mm × 100 mm cylindrical coral concrete specimens were prepared and cured in freshwater, seawater and oxalic acid in this study. The specimens were cured for 7, 14, 28, 60 and 90 days, respectively. The physical and mechanical properties of the specimens under the lossless state and static failure state were tested through piezoelectric transducer (PZT) test and uniaxial compression test. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed for analyzing the mineral composition and microstructure of the specimens. The results show that the compressive strength of the specimens in seawater and freshwater initially increased and then stabilized with the curing age, whereas in oxalic acid it initially increased and then decreased. The compressive strength of the specimens at 90 days in freshwater, seawater and oxalic acid solution have increased by 54%, 18% and 21%, respectively, compared to that at 7 days. A combination analysis using microscopic and macroscopic test indicated that the completion time required for hydration in freshwater, seawater and oxalic acid solution was 28, 28 and 60 days, respectively. This study suggests that Cl− in seawater accelerates the cement hydration process, improving the early mechanical properties of specimens. During the later hydration process, the soluble CaCl2 and expansile Mg(OH)2 generated during the later hydration process which reduces the strength. In oxalic acid solution, a dense calcium oxalate coating produced through the reaction between oxalic acid and CaCO3 would reduce the degree of hydration. The formation of CO2 would increase the porosity of specimens, thereby weakening the mechanical strength of the concrete.

A high-throughput technique to evaluate the probability distribution of strength of adhesively bonded joints after moisture absorption

ABSTRACT The reliability of adhesive bond strength influences the applicability of structural adhesives in industries. The statistical probability distribution of the strength of adhesive joints is an essential indicator when designing and choosing adhesives. In this study, we experimentally studied the probability distribution of the strength of adhesive joints. The strength data were collected using a novel high-throughput technique consisting of a sample preparation method and shear testing device. Numerous cylindrical butt shear-joint specimens were prepared by mechanical machining and tested using a self-developed shear testing device. The effect of moisture absorption by the adhesive was specifically considered. The probability distribution of the shear strength of the epoxy adhesive joints was characterized using five probability distribution functions: Normal, Lognormal, Exponential, Weibull, and Gamma. Quantile – quantile plots were employed to determine the suitability of each distribution function. The results suggested that the Weibull and Normal distributions were best suited for describing the probability distribution of the strength of the epoxy adhesive joints. The Weibull distribution is particularly suitable for brittle epoxy adhesives. Moisture absorption reduced both the mean and variance of the shear strength, which might be attributed to the plasticization of the adhesives. The high-throughput method proposed in this study significantly improved the efficiency of testing adhesive joints. It not only contributes to the study of the strength distributions of adhesive joints but also helps to shorten the research and development cycle of new adhesives by facilitating rapid strength evaluation.