Increase In Elastic Modulus Research Articles

Dynamic properties of mortar with oyster shell sand replacement

With the rapid expansion of construction engineering, the demand for traditional materials, particularly natural river sand, has surged, resulting in excessive resource exploitation and significant ecological damage. In response, the use of waste oyster shells as a sustainable alternative for fine aggregates has gained attention. However, limited research has been conducted on the dynamic properties of mortar with this substitution. This study explores the potential of using crushed oyster shell sand (OSS) as fine aggregates in mortar. A series of Split Hopkinson Pressure Bar (SHPB) tests under different gas pressures (pg) (0.2, 0.3, and 0.4 MPa) were carried out on mortar samples with five OSS replacement ratios (Rr) (0%, 20%, 50%, 80%, and 100%), using a water-to-cement ratio of 0.55. The results showed that when the OSS replacement rate (Rr) increased from 0 to 20%, there was a significant increase in peak stress (σmax) and elastic modulus (E), attributed to the filling effect of OSS, which enhanced the absorbed energy (Eab) and strength contribution rate (SCR). However, at Rr above 20%, a sharp decline in σmax and E was observed, primarily due to porous characteristics of OSS. Correspondingly, Eab decreased, reducing the impact resistance of mortar. Moreover, the negative SCR suggests detrimental effects on mortar integrity at higher OSS Rr levels. Predictive relationships for peak stress and elastic modulus across different replacement ratios were established in this study, providing a foundational reference for the design and assessment of the dynamic mechanical response of structures incorporating OSS.

Experimental research on mechanically and thermally activation of nano-kaolin to improve the properties of ultra-high-performance fiber-reinforced concrete

Abstract The rising demand for ultra-high-performance concrete (UHPC) necessitates innovations in sustainable materials. This study explores the substitution of ordinary Portland cement (OPC) with thermally and mechanically activated nano-kaolin in varying proportions from 0.5 to 0.25%. A uniform quantity of double-hooked end steel fibers was added to all the mixes. Activated nano-kaolin variants showed significant enhancement in UHPC properties. Specifically, UHPC with 0.20% thermally activated kaolin (B3-TAK-20) exhibited a 21.6% increase in compressive strength and a 25.5% increase in modulus of elasticity at 90 days, with the modulus of rupture doubling compared to the reference mix. These improvements are attributed to the amorphous nature of thermally activated nano-kaolin, resulting in a denser concrete matrix and reduced porosity. Beyond the optimal 0.20% kaolin replacement, an increase to 0.25% diminished compressive strength. Durability tests showed enhanced acid resistance, with only a 6.7% mass loss for the thermally activated nano-kaolin mix and a consistent reduction in water absorption by 14.4% as kaolin proportions increased from 0.5 to 0.25%. The study also noted a decrease in water absorption by 22.9 and 12.3% at 56 and 90 days, respectively, indicating the thermally activated nano-kaolin’s enhanced performance. This research underscores the potential of activated kaolin as a viable alternative to OPC, paving the way for more sustainable UHPC production.

Synergistic Integration of α-Ag2WO4 into PLA/PBAT for the Development of Electrospun Membranes: Advancing Structural Integrity and Antimicrobial Efficacy.

The rising resistance of various pathogens and the demand for materials that prevent infections drive the need to develop broad-spectrum antimicrobial membranes capable of combating a range of microorganisms, thereby enhancing safety in biomedical and industrial applications. Herein, we introduce a simple and efficient technique to engineer membranes composed of polylactic acid (PLA) and polybutylene adipate terephthalate (PBAT) biopolymers and α-Ag2WO4 particles using an electrospinning technique. The corresponding structural, thermal, mechanical, and antimicrobial properties were characterized. X-ray diffraction (XRD) patterns confirmed the integration of crystalline α-Ag2WO4 within the polymer matrix. Scanning electron microscopy (SEM) and Raman confocal microscopy revealed uniformly dispersed α-Ag2WO4 particles in the electrospun fibers, influencing their diameter and surface roughness. Thermal analysis indicated adjustments in the thermal stability and crystallinity of the composites with an increasing α-Ag2WO4 content. Dynamic mechanical analysis (DMA) highlighted variations in storage modulus and glass transition temperatures due to interactions between α-Ag2WO4 and polymer chains, with tensile tests showing an increase in elastic modulus and ultimate tensile strength as the α-Ag2WO4 content increased. Antimicrobial assessments revealed that PLA/PBAT membranes with α-Ag2WO4 showed pronounced antibacterial activity, forming inhibition halos across all samples against Pseudomonas aeruginosa, methicillin-resistant Staphylococcus aureus, and Mycobacterium smegmatis (a surrogate for Mycobacterium tuberculosis). These membranes also exhibited potent antiviral activity against bacteriophage phi 6, a surrogate for SARS-CoV-2, suggesting potential applications in combating infections caused by enveloped viruses. The antimicrobial activities are attributed to the generation of reactive oxygen species (ROS) and the controlled release of Ag+ ions. This work underscores the multifaceted capabilities of α-Ag2WO4-enhanced PLA/PBAT membranes in combating bacterial and viral growth, where both durability and microbial resistance are critical. Taken together, our findings provide a solution for obtaining advanced materials to be applied in a wide range of industrial applications, such as filtration systems, food preservation, antimicrobial coatings, protective textiles, and cleaning products.

Stereochemical Shape Morphing in Diels-Alder Polymer Networks.

The intrinsic reversibility of dynamic covalent bonding, such as the furan-maleimide Diels-Alder (DA) cycloaddition reactions, enables reprocessable, self-healing polymer materials that can be reconfigured via the mechanism of solid-state plasticity. In this work, the temperature-dependent exchange rates of stereochemically distinct endo and exo DA bonds are leveraged to achieve tunable, temperature- and stress-activated shape morphing in Diels-Alder polymer (DAP) networks. Through thermal annealing, ≈35% of endo DA isomers are converted in neat DAP networks to the thermodynamically favored exo form, achieving ≈97% exo after complete annealing at 60°C. This conversion results in a ≈1.7 fold increase in elastic modulus, from 1.7 to 3.0MPa, and significantly alters the stress relaxation and shape recovery behavior. Spatially resolved annealing, is further showcased enabling the precise control of spatial distributions of endo and exo DA bonds across planar geometries. The locally distinct concentrations of endo/exo isomers, achieved by temperature-induced conversion of endo DA isomers to the thermodynamically stable exo DA isomers, gave rise to the spatial distributions of stress relaxation rates and elastic strain recovery mismatch to enable controlled stereochemical shape morphing. This approach provides a simplified, thermally driven method for shape morphing, with potential applications in soft robotics and flexible electronics.

BIOMECHANICAL ASPECTS OF IMPACTION BONE GRAFTING IN THE ACETABULAR REVISION (EXPERIMENTAL AND CLINICAL WORK)

Introduction. The modern features of the revision hip arthroplasty are the increase of the number early revisions and young age of patients. Bone defect management in this category is especially relevant. The leading role in long-term survival using impaction bone grafting (IBG) is given to the mechanical properties of the graft. The purpose of the study is to explore the mechanical properties of osteoplastic material and determine the effect of cyclic loads on dynamic changes in the position of the acetabular component after revision hip arthroplasty using (IBG). Materials and methods. A single-cycle constrained compression experiment was carried out on morselized xenobone. Cyclic tests were carried out at the second stage of the study. Clinical interpretation of biomechanics was carried out on the radiographic data by changes in the acetabular position. Results. Stress-strain dependences and instantaneous elastic moduli were obtained. The increase of the instantaneous elastic modulus during cyclic tests was obtained by 2.6 times for a “dry” specimen and from 3.9 to 4.7 times with liquid. The shift of the center rotation cranially and laterally was noted in the first case is 2.4 and 1.5 mm, in the second is 14.9 and 9.5 mm, respectively. The change in the inclination was 18.7º in the first case and 19.8º in the second. The Hip Harris Score (HHS) was 97 points in the first case, 53 points in the second. Conclusions: 1. The material used for IBG is subject to deformation in the postoperative period. 2. Compression tests suggested that the deformation of impacted bone graft in the postoperative period gradually tends to reach a plateau, and with the completion of the deformation, migration of the acetabular component stops. 3. A change of the acetabular component position in the absence of a radiolucent line is not an absolute sign of loosening.

Study on the aging behavior and mechanism of nitrile rubber composites in combined radiation-thermal environments

This contribution investigates the aging property changes and mechanism of nitrile rubber (NBR) under the combined radiation-thermal environments in the N2 atmosphere. Aging resulted in a decrease in elongation at break from 309.01 % to 64.74 %, an increase in modulus of elasticity from 3.84 MPa to 9.09 MPa, and a slight increase in thermal stability. The crosslink density increases and the mass loss of the sample is reduced, while the chemical structure of the sample surface is almost intact. By gas-phase infrared spectroscopy, the irradiation aging-induced gases from NBR were also analyzed, including CO2, CO, and alkanes (CH4, C2H6, C3H8). This indicates that chain scission and pendant group removal also take place, whereas chain breaking primarily occurs at the macromolecular chain end. The above degradation reactions and the decomposed additives account for the generated trace amount of small molecule gas products. These findings suggest that the primary aging mechanisms of NBR are the cross-linking of macromolecular chains and additive loss. Furthermore, radiation and thermal have a synergistic effect on NBR aging, and this effect has a threshold temperature that is clearly between 50 °C and 70 °C. The synergistic effect of additive cleavage is only apparent at temperatures above 65 °C under radiation-thermal conditions.

Compressive properties and microstructure of hybrid fiber-reinforced fly ash/slag-based geopolymers at elevated temperatures

This study investigates the effects of fly ash ceramsite (FACM) and hybrid fibers (with varying steel fiber contents) on the mass loss, compressive performance, crack development, and microstructure of hybrid fiber-reinforced fly ash/slag-based geopolymers (HFRG) at high temperatures. HFRG samples with different steel fiber volume fractions (0%, 0.5%, 1%, and 1.5%) were prepared and subjected to a controlled heating process (20°C, 200°C, 400°C, 600°C, and 800°C). Key properties, including mass loss, compressive strength, and crack patterns, were measured at elevated temperatures, with additional microstructural analysis conducted via SEM, XRD, and FTIR. Results showed that a 0.5% steel fiber content can suppress mass loss at high temperatures, while 1% steel fiber significantly enhances HFRG's compressive performance under heat. Compared to HFRG-0, HFRG-1.0 showed a 39% increase in peak stress, a 41% increase in strain, a 4.7% increase in elastic modulus, and a 108% increase in energy absorption capacity at 200°C. Surface observations revealed that crack area significantly decreased with increased steel fiber content. Microstructural analysis indicated that internal porosity increases, and thermal decomposition intensifies with rising temperature. This study provides key insights into the axial compression performance of HFRG for high-temperature applications and offers a detailed analysis of the effects of lightweight aggregates and hybrid fibers.

Diffusion law and diffusion model for backfill grouting in loess shield tunnel at different soil moisture

Loess is a special type of soil whose properties are significantly affected by water. However, the grout diffusion law for backfill grouting in loess shield tunnels remains unknown. Based on a visual model experimental device, three experiments were conducted with 10%, 20%, and 30% loess moisture. A finite discrete element method was used to verify the grout diffusion mode, and parameters such as the tunnel buried depth, grout viscosity, and elastic modulus were considered to analyse the grout diffusion law. Experiments and numerical simulations show that the screening diffusion of grout occurs at low loess moisture, whereas splitting diffusion occurs at high loess moisture. The farthest splitting diffusion distance decreases as the tunnel buried depth, grout viscosity, and elastic modulus increase. In addition, based on capillary theory and geotechnical strength criteria, screening diffusion and splitting diffusion models were established. This study investigated the grout diffusion law and grout diffusion model, providing a reference for the design and construction of loess shield tunnels.

Analysis of mechanical properties of single crystal copper under low-temperature indentation test

Abstract As a common superconducting material in the aerospace field, the mechanical properties of single-crystal copper at low temperatures have attracted much attention. Combined with the current low-temperature nanoindentation test technology and the research status of micromechanical properties of crystal copper at home and abroad, this paper puts forward the low-temperature nanoindentation test on single-crystal copper. It analyzes the changes in mechanical properties of the low-temperature environment by indentation curve. Before the formal test, we first analyzed the Oliver-Pharr micro and nanoindentation test theory and described briefly the advantages of using nanoindentation to test the mechanical properties. The final test results show that in the temperature range of 300K~150K, the hardness and elastic modulus of the single-crystal copper increase with the decrease in temperature. The lower the temperature is, the faster the increase of hardness and elastic modulus is. At the same temperature, the hardness and elastic modulus of single-crystal copper with three crystal faces are (111) > (110) > (100). The mechanical properties at low temperatures are effectively reflected by means of low-temperature nanoindentation, which can be used to guide the production of materials in real life.

Micromechanical properties and fractal homogenization of coal based on nanoindentation

Distinct from hard rock, coal is relatively soft and fragmented. It is not only challenging to prepare test coal samples that meet the requirements of standard mechanical experiments but also impossible to recycle them for repeated testing. There is an urgent need to explore new mechanical testing methods to enhance the study of the mechanical properties of coal. In this study, the micromechanical parameters of the coal matrix solid phase were acquired through targeted nanoindentation technology. The elemental composition, surface morphology, and pore structure characteristics of each indentation point were determined by energy dispersive spectrometer, optical microscope observation, and high-pressure mercury injection experiments. The fractal homogenization equation is deduced based on fractal geometry and the Mori–Tanaka method. The validity of the fractal homogenization approach is verified by integrating the micromechanical parameters and pore structure characteristics of coal, and the impact of the microstructural parameters on the macroscopic mechanical properties of coal is discussed. The results show that the proportion of clay minerals in the solid phase of the coal is the greatest (81.18%), with the main mineral components being kaolinite and illite. The elastic modulus is 1.974 ± 1.036 GPa, the hardness is 0.131 ± 0.108 GPa, and the ratio of upper and lower pore scales conforms to the fractal calibration rate. The macroscopic equivalent elastic modulus rises along with the increase in the fractal dimension. When the fractal dimension is constant, the macroscopic equivalent elastic modulus decreases with the increase in λmin/λmax and increases with the increase in solid phase elastic modulus.

Microstructure evolution and corrosion behavior of metastable β Ti-18.4Nb-5Zr alloy with low modulus after thermomechanical treatment

In this paper, the effects of precipitate phases on the mechanical properties and corrosion resistance of newly developed β-type Ti-18.4Nb-5Zr (at. %) (TNZ) alloy after thermomechanical treatment that combines cold rolling (CR) with annealing were investigated. With the cold rolling reduction rate to 94%, nano-grained (NG) TNZ alloy with average grain size about 34 nm was produced and the alloy was composed of β phase, α″ phase and ω phase. After short-time annealing, a small amount of α phase and fine athermal ω phase are precipitated, which promoted the disappearance of stress-induced α″ phase. As the annealing temperature increased, the α phase transformed to the β phase and the athermal ω phase gradually disappeared. The number and size of α phase and athermal ω phase increase with the increase of annealing time, which promoted the increase of elastic modulus and plasticity. After polarization treatment in Hank's solution, the corrosion resistance of TNZ alloy was improved and a double-layer film structure was formed. But the corrosion rate of the alloy surface increased significantly with annealing time. The NG alloy after annealing at 550 °C / 10 min exhibited good corrosion resistance and mechanical properties with elastic modulus of 28.4 ± 3.6 GPa, which matched with human bone.

Novel ellipsoid-like granules exhibit enhanced anammox performance compared to sphere-like granules

Anammox granular sludge (AnGS) serves as an important platform for cost-effective nitrogen removal from wastewater. Different to the traditionally sphere-like granules, a novel type of AnGS in a unique ellipsoid-like shape was obtained through enhancing shear force. The ellipsoid-like AnGS significantly exhibited a smaller aspect ratio (-25.1 %) and granular size (-11.8 %), compared to traditional sphere-like AnGS (p < 0.01). Comprehensive comparisons showed that ellipsoid-like AnGS possessed a significantly higher extracellular polymeric substances (EPS) content and strength, as well as an enhanced mass transfer and a higher viable bacteria proportion due to the larger substrate permeable zone (p < 0.01). Additionally, the anammox bacterial abundance (Candidatus Kuenenia) was 12.2 % higher in ellipsoid-like AnGS than in sphere-like AnGS. All these characteristics of ellipsoid-like AnGS jointly increased the specific anammox activity by 29.0 % and nitrogen removal capacity by 22.6 %, compared to sphere-like AnGS. Further fluid field simulation suggested the enhanced flow shear on the side surface of AnGS likely drove the formation of ellipsoid-like AnGS. The higher shear force on the side surface led to an increase of EPS content (especially hydrophobic protein) and elastic modulus, thus constraining lateral expansion. This study sheds light on impacts of granular shape, an overlooked morphological factor, on anammox performance. The ellipsoid-like AnGS presented herein also offers a unique and promising aggregate to enhance anammox performance.

Analysis of Accelerated Weathering Effect on Polyethylene With Varied Parameters Using a Combination of Analytical Techniques

AbstractPlastics make up a great portion of solid waste that constitutes an emerging threat to the natural environment. Among plastics, polyethylene is the most widely used in the world. In this research, polyethylene materials with different densities designed for packaging applications are the subject of a degradation study. The materials were exposed to simulated solar exposure and were characterized by a combination of analytical techniques to compare both chemical and physical changes, including attenuated total reflection‐Fourier transform infrared spectroscopy (ATR‐FTIR), water contact angle measurements, Raman spectroscopy, grazing incidence X‐ray Diffraction (GIXRD) and nanoindentation tests. The experimental data were systematically analyzed using statistic methods. It was found that the extent of the increase of polar groups, hydrophilicity, crystallinity, and elastic modulus depends on both the density of polyethylene and the duration of UV aging. These changes result from photooxidation and the subsequent structure reorganization occurring in amorphous chains. The implementation of various analytical techniques and statistical analysis provides a holistic understanding of polyethylene degradation behaviors. The knowledge of increased hydrophilicity/polarity in polyethylene is crucial for understanding the fate of plastics in the environment because such polyethylene changes also facilitate the environmental biodegradation on initially non‐polar polyethylene.

Mechanical and Dimensional Stability of Gelatin-Based Hydrogels Through 3D Printing-Facilitated Confined Space Assembly.

Hydrogels have emerged as promising biomaterials for tissue regeneration; yet, their inherent swelling can cause deformation and reduced mechanical properties, posing challenges for practical applications in biomedical engineering. Traditional methods to reduce hydrogel swelling often involve complex synthesis procedures with limited flexibility. Inspired by nature's efficient designs, we present here the approach to improve hydrogel performance using 3D printing-assisted microstructure engineering. By utilizing polymerization-induced phase separation of hydrogel from copolymerization of gelatin methacrylate and hydroxyethyl methacrylate (poly(GelMA-co-HEMA)) in the confined space during vat photopolymerization (VPP) 3D printing, we replicate the cuttlebone-like microstructure of hydrogels with enhanced mechanical properties and swelling resistance. We demonstrate here a 4-fold increase in elastic modulus compared to bulk polymerization of poly(GelMA-co-HEMA), together with improved mechanical and dimensional stability. This method offers promising opportunities for practical biomedical and tissue engineering applications, overcoming previous limitations in the design and performance.

Analysis of differential scanning calorimetry data for aged plutonium.

Differential scanning calorimetry data for samples of a 52 year old plutonium alloy with 3.3 at. % Ga that were heated beyond the melting point is analyzed using transition state theory to find activation energies for the δ to ɛ and ɛ to liquid phase transitions. A Bayesian statistical method involving a Gaussian process model is used to find mean values and confidence intervals for the activation energies. The activation energy for the δ to ɛ phase transition increases by 3.3 ± 3.8% per decade, relative to the case when all age related plutonium lattice point defects have been removed through annealing. The corresponding increase in activation energy for the ɛ to liquid transition is shown to be 7.1 ± 1.8% per decade. It is postulated that the change in activation energy with age for both phase transitions is caused, in part, by the accumulation of the same type of lattice point defects associated with the observed increase in elastic bulk modulus over time.

Design of novel structural eutectic high entropy alloys (EHEAs) containing high-temperature resistant alloying elements

This article employs the “Simple Mixing Enthalpy Method” to add high-temperature alloying elements Mo/V and Nb to the Fe-Co-Cr-Ni-based alloy system, and utilizes a model of the relationship between elements and phase structures. Finally, EHEAs are successfully designed with the help of phase diagrams, namely FeCoNi2.0Cr1.2Mo0.2Nb0.63 (Mo0.2Nb0.63) and FeCoNi2.0Cr1.2V0.2Nb0.68 (V0.2Nb0.68). In EHEAs, a typical fully eutectic microstructure is observed, consisting of alternating FCC (face-centered cubic) and HCP (hexagonal close-packed) phases. Evaluation of mechanical performance indicators reveals that nano-hardness and elastic modulus increase from the FCC phase to the HCP phase, while the hardness and elastic modulus of the eutectic phase originate from modulation of these two phases. Meanwhile, the microhardness of both alloy systems increases linearly with increasing Nb content. In addition, EHEAs exhibit high strength and ductility but with differences attributed to the significant influence of Mo and V elements on eutectic phase spacing and phase size. Different phase interface types and strain gradients during deformation affect the mechanical properties. This study tests the high-temperature compression performance and fracture morphology of novel high-entropy alloys, paving the way for subsequent research on high-temperature performance.

Mechanics and Cutting Performance of Multilayer Nanostructured TiAlN/TiSiN/ZrN Coatings

The aerospace industry has made extensive use of titanium alloy material due to its exceptional qualities, which include high strength, low weight, and resistance to corrosion. However, these qualities also pose challenges for the material’s processing. This article examined the coated end mills for Ti6Al4V milling. First, an analysis was conducted on the solubility of Ti and Si elements. It was discovered that W and Co elements were far more soluble in Ti than Si and Zr elements, which could effectively stop element diffusion. Next, the base’s composition was planned. It was discovered that when the amount of Al increased, the base’s surface roughness increased, while its hardness and elastic modulus decreased. The binding force between the substrate and the base was greater at a 50:50 Ti:Al ratio. The H3/E2 was about 0.23 and the surface roughness was about 0.15 μm. TiSiN and TiSiN/ZrN functional layer properties were also examined. When Zr was added to TiSiN/ZrN coating, it improved the coating’s hardness and elastic modulus, increased density, and decreased surface roughness and friction coefficient when compared to TiSiN coating. There was an increase in hardness by 8.09% and an increase in elastic modulus by 9.65%. The average coefficient of friction decreased from 0.315 to 0.299. Lastly, an analysis of the initial and intermediate tool wear was done using the Ti6Al4V milling experiment. It was discovered that adding Zr element could successfully extend the tool’s cutting life by preventing adhesive wear.

Laser additive manufacturing of Ti and Ce co-modified 2195 difficult-to-process aluminum alloy: Grain refinement, cracking suppression and enhanced mechanical properties

High cracking susceptibility of Al-Li alloys with Ti/CeB6 addition is thoroughly suppressed in laser powder bed fusion (LPBF) processing of Ti/Ce co-modified 2195 alloys at relatively high scan speeds, while the cracking suppression mechanism and phase formation in these composites are not clarified. In this work, microstructure evolution and mechanical performance of the LPBF-fabricated Ti/Ce co-modified 2195 are investigated to reveal their cracking suppression and strengthening mechanisms. The results show that apparent grain refinement of the composites is ascribed to high supercooling from rapid formation of constitutional supercooling zone in front of solid–liquid interfaces by high-Q-value Ti solute, and heterogeneous nucleation of in situ formed Al3Ti and Al11Ce3 precipitates. Their synergistic interactions promote formation of fine equiaxed grains and thus inhibit crack initiation. The composites exhibit high microhardness of 100 ± 5 HV0.2, nano-hardness of 1.6 ± 0.1 GPa and elastic modulus of 97 ± 3 GPa, where the elastic modulus increases by ∼27% and ∼31% compared to those of LPBF-processed and conventionally manufactured 2195 alloys, respectively. A tensile strength of ∼336 MPa and an elongation of ∼3% are obtained from in-situ synchrotron X-ray diffraction measurement. The improved properties are derived from grain refinement and Orowan strengthening. Based on the optimal processing parameter and composition, a bracket component filled with lattice structures is designed and manufactured with good manufacturing quality and processing accuracy.

Physical, Structural and Elastic Properties of New Oxyfluoride Borate Glasses

New mixed alkali/alkaline oxyfluoride borate glasses with composition xCaF2–(50-x)LiF–50B2O3 (x = 0, 5, 10, 15 and 20 mol%) were prepared by the conventional melt-quenching technique. X-ray diffraction (XRD) patterns confirmed the amorphous nature of the prepared samples, while energy dispersive X-ray (EDX) analysis confirmed the presence of the constituent elements B, O, F, and Ca. Fourier transform infrared (FTIR) spectra revealed the formation of BO3, BO2F, BO4 and BOF3 structural groups, as well as non-bridging oxygen/fluorine atoms in the glass network. The concentrations of these structural groups were found to vary with CaF2 concentration. The measured density and the calculated molar volume were found to increase over the entire range of composition. The increase in ultrasonic velocity, elastic moduli, micro-hardness and Debye temperature with the addition of CaF2 was discussed in terms of competition between the above-mentioned borate groups. Fraction of four-coordinated boron atoms, average boron–boron separation, fluorine molar volume, total packing density, dissociation energy per unit volume and average cross-link density were estimated. A close correlation is achieved between these quantities and elastic properties. Excellent agreement is found between the experimentally determined values and the theoretically calculated values of elastic properties from Makishima–Mackenzie's theory.

Contact fatigue property of diamond-like carbon films with different structure in cyclic impact conditions

Repeated contact with high loads can cause damage to the surface of the DLC films and thus affect their fatigue strength. This study systematically investigates the contact fatigue damage of the DLC films with different carbon structures (a-C, a-C:H, and ta-C) by macro-scale cyclic impact tests with alternating loads. The results reveal that the a-C film possesses significantly superior contact fatigue property compared to the a-C:H and ta-C films under high load. The graphitization transformation of the a-C and a-C:H films lead to a decrease in hardness and elastic modulus. The work-hardening of the ta-C films results in an increase in hardness and elastic modulus. The findings indicate that under cyclic load impact conditions, films need a combination of load support and fatigue resistance to achieve optimum lifetime, and solely increasing film hardness could be accompanied by brittle fracture and higher wear.