Contact Hardness Research Articles

Correlation between the Chemical Structure of (Meth)Acrylic Monomers and the Properties of Powder Clear Coatings Based on the Polyacrylate Resins.

This paper presents studies on the influence of the chemical structure of (meth)acrylic monomers on the properties of powder coatings based on polyacrylate resins. For this purpose, a wide range of monomers were selected-2-hydroxyethyl methacrylate (HEMA), methyl methacrylate (MMA), n-butyl acrylate (nBA), tert-butyl acrylate (tBA), dodecyl acrylate (DA), ethyl acrylate (EA) and benzyl acrylate (BAZ)-for the synthesis of the polyacrylate resin. The average molecular mass and molecular mass distribution of the synthesized resins were measured by gel permeation chromatography (GPC). The glass transition temperature (Tg) and viscosity of polyacrylate resins were determined by using differential scanning calorimetry (DSC) and a Brookfield viscometer. These parameters were necessary to obtain information about storage stability and behavior during the application of powder clear coatings. Additionally, DSC was also used to checked the course of the low-temperature curing reaction between the hydroxyl group contained in the polyacrylate resin and the blocked polyisocyanate group derived from a commercial agent such as Vestanat B 1358/100. The properties of the cured powder clear coatings were tested, such as: roughness, gloss, adhesion to the steel surface, hardness, cupping, scratch resistance, impact resistance and water contact angle. The best powder clear coating based on the polyacrylate resin L_HEMA/6MMA/0.5nBA/0.5DA was characterized as having good scratch resistance (550 g) and adhesion to the steel surface, a high water contact angle (93.53 deg.) and excellent cupping (13.38 mm). Moreover, its crosslinking density (CD) and its thermal stability was checked by using dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA).

Preparation and characterization of biodegradable starch foam composite with treated Khlum fiber for food packaging

AbstractStarch foam is a completely biodegradable material that can replace petroleum‐based foams. However, starch foams are sensitive to water and have poor mechanical properties. Khlum fiber that had been alkali‐treated for 1 h (KF‐1h) showed excellent properties as a reinforcement of starch foam. KF‐1h was added to starch at loadings of 0, 1, 3, 5, and 7 wt%. The starch foam composite reinforced with 1 wt% of KF‐1h presented uniformly distributed cells of uniform size, and produced the highest values for flexural stress at maximum load (3.43 MPa), hardness (92.50), and water contact angle (122°) of the studied foams. The modulus of the starch foam composite increased with increments of KF‐1h content but the density and color of the starch foam and the biodegradation process in soil were only slightly affected. This work also demonstrated a practical application of the proposed starch foam composite as a biodegradable food container.

Influence Evaluation of Tungsten Content on Microstructure and Properties of Cu-W Composite

At present, most studies focus on Cu-W composites with high W content (W content > 50 wt%), while there are only sporadic reports on Cu-W composites with low W content (W content < 50 wt%). In this work, Cu-W composites with different W contents (0, 10 wt%, 20 wt% and 30 wt%) were prepared, and the effects of W content on microstructure, density, hardness, electrical conductivity, strength and electrical contact properties were systematically studied, with the expectation of providing an experimental basis and theoretical support for expanding the application range of Cu-W composites with low W content. The results showed that, with the increase in W content, the Cu matrices divided into finer and more uniform grains; the density and electrical conductivity of Cu-W composites decreased; and the compressive yield strength and hardness gradually increased. As the content of W increased, the arc burning time of the Cu-W composite contacts began to fluctuate. There was a loss of both the cathode and the anode contacts of the pure Cu, but the mass transfer of the Cu-W composite contacts occurred as follows: the anode weight increases, while the cathode weight decreases. The addition of W particles changed the non-uniform ablation of the pure Cu, and the surface ablation of the Cu-W composite contacts remained uniform.

Cotton waste and nanoclay‐based phenolic novolac epoxy composites and evaluation of their properties

AbstractIn this study, two types of biobased epoxy composites were prepared by using only alkali‐treated cotton waste (CtW), or with the nanoclay (NC) in the form of hybrid reinforcement. Phenol novolac‐type epoxy resin (EPN) was used as a matrix. Untreated (CtW) and alkali‐treated (NaOH‐CtW) particles were characterized by scanning electron microscopy (SEM)/energy‐dispersive X‐ray spectroscopy (EDX). The average size for NC was determined as 3838 nm. Composites were prepared at 10–50 wt% NaOH‐CtW and 20 wt% NaOH‐CtW/(1–2–3–4–5) wt% NC ratios. The morphology of the composites was investigated using SEM. The composites' properties were determined by applying thermogravimetric analysis (TGA), and various tests (tensile, hardness, water sorption, and surface contact angle measurement). The tensile strength of pure EPN was 96.6 MPa, while it changed in the range of 74–98 and 81–106 MPa for NaOH‐CtW and hybrid composites, respectively. All hybrid composites exhibited higher Young's modulus values (7.7–8.9 GPa). Thermal values of hybrid composites were found higher and their char percentages varied in the range of 28.9–30.3%. NaOH‐CtW increased the water sorption of the epoxy matrix from 0.59% up to 6% by 50 wt%. In contrast, a decrease in water sorption of NC composites was observed.

Microporous structures on mineralized collagen mediate osteogenesis by modulating the osteo-immune response of macrophages.

It is a new hot pot in tissue engineering and regenerative medicine to study the effects of physicochemical properties of implanted biomaterials on regulating macrophage polarization to promote bone regeneration. In this study, we designed and fabricated mineralized collagen (MC) with different microporous structures via in vitro biomimetic mineralization method. The microporous structures, mechanical properties, shore hardness and water contact angle measurements were tested. Live/dead cell staining, CCK-8 assay, phalloidine staining, staining of focal adhesions were used to detect cell behavior. ELISA, qRT-PCR, ALP, and alizarin red staining (ARS) were performed to appraise osteogenic differentiation and investigated macrophage response and their subsequent effects on the osteogenic differentiation. The results showed that RAW264.7 and MC3T3-E1 cells were able to survive on the MC. MC with the microporous structure of approximately 84 μm and 70%–80% porosity could promote M2 macrophage polarization and increase the expression level of TGF-β and VEGF. Moreover, the gene expression of the osteogenic markers ALP, COL-1, and OCN increased. Therefore, MC with different microporous structures mediated osteoimmunomodulation in bone regeneration. These data will provide a new idea of biomaterials inducing bone repair and direct the optimal design of novel immune biomaterials, development, and rational usage.

Polyacrylate resins containing fluoroalkyl groups for powder clear coatings

This work focuses on the synthesis of polyacrylate resins containing fluoroalkyl groups, which are used to prepare powder clear coatings. The resin synthesis was carried out using 2-hydroxyethyl methacrylate (HEMA), methyl methacrylate (MMA), n-butyl acrylate (BA), 2-phenoxyethyl acrylate (PhEA) as well as two acrylate monomers containing fluoroalkyl groups, i.e. 2,2,2-trifluoroethyl methacrylate (TFEMA) and 2,2,2-trifluoroethyl acrylate (TFEA). The presence of fluorine in the resin was confirmed by 19F NMR spectroscopy, while at the coating surface by polarized optical microscopy equipped with a laser elemental analyzer. Gel permeation chromatography (GPC) was used to determine the average molecular mass and molecular mass distribution of the synthesized resins. Additionally, the viscosity measurement of the resins was performed using a Brookfield viscometer. The thermal behavior of the powder coatings was investigated using differential scanning calorimetry (DSC). Moreover, FT-IR spectra were performed to confirm the crosslinking reaction between hydroxyl groups of the resin and polyisocyanate curing agent. The properties of the cured coatings were tested, such as: roughness, gloss, adhesion to the steel surface, hardness, cupping, scratch resistance and water contact angle. The obtained coatings were characterized by good properties: gloss, adhesion to the steel surface, scratch resistance, and hydrophobicity.

High temperature oxidation and tribological properties of cemented carbide material under different cooling condition

For further clarify the correlation mechanism between the high temperature oxidation and tribological properties of cemented carbide, two groups of test samples of YT15 cemented carbide were prepared and heated to 500 °C ~ 900 °C, then cooled to room temperature in air and cutting fluid medium respectively. The surface morphology, oxidation characteristics, hardness, wettability, and tribological property were measured with white light interferometer, XRD instrument, contact angle measuring instrument, and MWF-500 friction tester. Experimental results indicate that the surface roughness and oxidation degree are increased with the increasing of heating temperature and independent of the cooling medium. Thus, a decrease law of friction coefficient and a worsening trend of surface wear quantity are observed due to low surface hardness under dry friction condition. For cutting fluid lubricating case, the friction coefficient of test sample is firstly decreased with the heating temperature increasing, and then an increased trend is occurred when the heating temperature is more than 800 °C. The main reason is that more wear particles are produced due to the low surface hardness and big contact pressure which deteriorated the lubrications conditions. The main contribution of this work is in providing a reference resources for the tool surface wear mechanism.

A General Approach to Determine the Constitutive Parameter Dependence of Global Quantities at Sharp Contact Testing of Rigid-Plastic Materials

Correlation of sharp contact problems is investigated with the focus on rigid-plastic contact behavior pertinent to engineering metals and alloys. The aim is to determine relations between the contact hardness and constitutive parameters suitable for material characterization. This is performed by using a solution approach where the transition zone between elastoplastic and rigid-plastic contact behavior is analyzed, especially as regards the size of the plastic zone. This approach is applied to three different cases: (1) sharp indentation of von Mises plastic materials; (2) sharp indentation of Drucker–Prager plastic materials; (3) sharp scratching of von Mises plastic materials. Established finite element simulations are used in order to verify the analysis of these three cases. In addition, based on the suggested approach, new results concerning the constitutive parameter dependence of the relative contact area, pertinent to case (2) above, are presented and compared with finite element simulations. All of the results are valid for metals and alloys but also for elastic–plastic crystalline materials where the contact deformation regime is close to the rigid-plastic one.

The Contact Mechanics for Indentation of Single Asperity and Rough Surfaces

Abstract A finite element analysis of a rigid sphere contact with a deformable elastic–plastic plat called indentation model is studied. The numerical results are applied on the rough surfaces contact of the Greenwood-Williamson (G-W) model. A series of the relationships of the rough surfaces contact parameters are obtained. The contact parameters of the indentation model and the flattening model are compared in detail, and the reasons for their differences are analyzed. In the case of single asperity contact, for ω/ωc > 1, the indentation model reaches the initial plastic yield while the flattening model is ω/ωc=1. In ω/ωc=10, the plastic yield reaches the contact surface for the first time, and the corresponding point of the flattening model is relatively earlier in ω/ωc=6. The contact parameters of the rough surface in different plasticity indexes are compared again. On the point of ψ = 0.5, the contact parameters of the flattening model and the indentation model coincide perfectly. For 0.5 < ψ < 4, the difference between the parameters curves become larger and larger. To the point of ψ = 4, when the distance difference reaches the maximum, it begins to decrease until the two curves are close to coincide again. The dimensionless elastic–plastic contact hardness is introduced. The relation between the real contact area and the contact pressure of the indentation model can be acquired quickly. The results show that the geometric shape of deformable contact parts has an important effect on the contact parameters, especially for the extension of the plastic deformation region within a specific range of plasticity index.

In-situ SEM cyclic nanoindentation of pre-sintered and sintered zirconia materials

Efficient diamond machining of zirconia requires a comprehensive understanding of repetitive diamond indentation mechanics. This paper reports on in-situ cyclic nanoindentations of pre-sintered and sintered zirconia materials performed inside a scanning electron microscope (SEM). In-situ SEM imaging of cyclic indentation processes and high-magnification SEM mapping of indentation imprints were conducted. The elastic and plastic behaviors of pre-sintered and sintered zirconia materials were investigated as a function of the cyclic nanoindentation number using the Sakai and Sakai-Nowak models. For pre-sintered zirconia, cyclic nanoindentation induced quasi-plastic deformation, causing localized agglomeration of zirconia crystals with microcracks and large cracking along the indentation edge. Severely compressed, fragmented, and pulverized zirconia crystals and smeared surfaces were also observed. For sintered zirconia, shear bands dominated quasi-plastic deformation with the formation of edge pile-ups and localized microfractures occurred at indentation apex and diagonals. All elastic and plastic behaviors for pre-sintered and sintered zirconia materials revealed significantly microstructure-dependent. Pre-sintered zirconia yielded significantly lower contact hardness, Young's moduli, resistance to plasticity, elastic deformation components, and resistance to machining-induced cracking, and higher elastic and plastic displacements than sintered state. Meanwhile, all the behaviors for the two materials were independent from the cyclic nanoindentation number. A model was proposed for cyclic nanoindentation mechanics, revealing their cyclic indentation-induced microstructural changes in the two zirconia materials. This study advances the fundamental understanding of nanoindentation mechanics of zirconia materials.

Assessment of Coating Zirconium Implant Material with Nanoparticles of Faujasite

Aim: To evaluate the wettability and microhardness of Zirconium (ZrO2) dental material when coated with different concentrations of Faujasite. Materials and methods: 30 circular disks produced from ZrO2, then each group is classified into 10 control groups, 10 coated groups with 3% Faujasite, and 10 coated groups with 7% faujasite by electro-spun tool to study variable properties in hardness and water contact angle of implant materials. Results: This study stated the high hardness in 7% of faujasite concentration for ZrO2, in addition, the contact angle decreased gradually until reach 0 ᵒ in 7% concentration of faujasite with ZrO2 Conclusion: Water contact angle (WCA) declined till disappeared in (7% wt.) of faujasite coated with the ZrO2 group, also in the same group the microhardness became high compared with other groups due to alteration in surface morphology of substrate, and properties of coated material.

Synthesis and properties of vinyl benzyl alcohol copolymers with styrene

Objectives. Synthesis and study of the properties of copolymers of vinyl benzyl alcohol (VBA) with styrene with antimicrobial properties.Methods. The study employed infrared (IR) and nuclear magnetic resonance (NMR) spectroscopy, thin-layer chromatography, viscometry, and elemental analysis. The sessile drop method and the pencil method were respectively utilized to determine the contact angles and hardness of the films. The process of testing the film coatings’ resistance to the effects of molds consisted of contaminating the film coatings applied to the glass with mold spores of the All-Russian Collection of Microorganisms in a solution of mineral salts without sugar (Czapek–Dox medium).Results. Homopolymers of vinyl benzyl acetate and its copolymers with styrene were synthesized in this study. Homo- and copolymers of VBA were obtained by saponification. IR and proton NMR (1H NMR) spectroscopy determined the composition of the copolymers. Employing IR spectroscopy, the degree of saponification was monitored by the appearance of the hydroxyl group absorption band and the disappearance of the ester group absorption band. According to the IR spectroscopy data, only an insignificant (~3%) amount of ester groups remains in the saponified copolymers. The influence of the copolymers’ composition on their solubility in various solvents is demonstrated. IR spectroscopy of the copolymers revealed hydrogen-bond formation between the unreacted ester groups and hydroxyl groups formed due to the saponification. The viscometry of the solutions of mixtures of saponified and unsaponified copolymers, solutions of mixtures of saponified copolymer with polyvinyl acetate, and viscometry of saponified copolymers in various solvents all support this conclusion. These bonds’ concentration depends on the copolymer’s composition and can be controlled by the nature of the solvent from which these copolymers’ films are formed. Saponified copolymer solutions form smooth, transparent film coatings with excellent adhesion to metals and silicate glass surfaces. The contact angle of these films, like the hardness, decreases as the VBA units’ concentration in the copolymers increases and depends on the solvent polarity used to form the films. It has been demonstrated that increasing the VBA units concentration suppresses the microorganisms’ growth.Conclusions. Film coatings made of copolymers of styrene with VBA have been shown to have high biocidal activity against molds; can be used to protect structural materials and products from the effects of microorganisms.

Experimental Study on the Properties of Copper Base Alloy by Laser Cladding on the Surface of Pure Copper Contact

Arc ablation is the main reason for the failure of pure copper switches. In order to improve the electric ablation resistance of pure copper contacts, Cu-W-Ni alloy cladding layers with different tungsten contents were prepared on the surface of pure copper matrix by laser cladding technology. The microstructure, composition distribution, hardness and corrosion resistance of the cladding layer were analyzed. The results show that the surface of the cladding layer and the pure copper matrix is metallurgical, without holes, cracks and other defects, and the dilution rate is low, and the average hardness is significantly increased. On the whole, the comprehensive properties of CuW10Ni3 cladding layer are slightly better than the other two Cu-W-Ni cladding layers. Compared with the pure copper matrix, the contact hardness is significantly improved under the premise of ensuring the electric conductivity of the inner pure copper matrix.

Effect of Ni, N Co-Doped on Properties of AgSnO2 Contact Materials

The first-principles method based on density functional theory was used to analyze the impurity formation energies, energy bands, density of states, electron overlap population and elastic modulus of SnO2, SnO2–Ni, SnO2–N and SnO2–Ni–N. SnO2 powders with different additives were prepared by the sol-gel method, and then X-ray diffraction experiments and wettability experiments were carried out. The powder metallurgy method was used to prepare AgSnO2 contacts with different additives. The simulation experiments on hardness, electrical conductivity and electrical contact were carried out. The simulation results show that the conductivity of Ni–N co-doped SnO2 is best, and more impurity levels are introduced into the forbidden band, thereby increasing the carrier concentration, reducing the band gap, and improving the conductivity. The experimental results show that Ni, N doping does not change the structure of SnO2, so doped SnO2 still belongs to the tetragonal system. Ni–N co-doping can better improve the wettability between SnO2 and Ag, reduce the accumulation of SnO2 on the contact surface and reduce the contact resistance. Ni–N co-doped SnO2 has the smallest hardness, improving ductility, molding and service life of the AgSnO2 contact material.

Exploitation of static and dynamic methods for the analysis of the mechanical nanoproperties of polymethylmetacrylate by indentation

The development of instrumented nanoindentation consists of non-destructive tests applied to miniature volumes of material (PMMA). The present research focuses on the factors explaining the variation in the trends of the mechanical properties studied. The evolution of Young's modulus (E) and contact hardness (H) with depth (h) and indentation force (P) shows the existence of an inflection point (2.77 nm) at low penetrations which separates two zones with the first increasing trend and the second decreasing. Explained respectively by the surface hardening induced by the preparation of the material surface and the existence of a surface hardness gradient denoted by the indentation size effect (ISE) observed at very low depths. In addition, on detection of a critical penetration depth below which the effect of the surface on the nanohardness dominates, the variation in the penetration charge is of the order of 9.71 nm. The differences in results of E and H between the dynamic and static modes are of the order of 8.46% and 6.44% inducing an overestimation of 35 MPa in value of E and an underestimation of 1.23 MPa in value of H. They tend to affect the expected nanoscale precision of the indentation to determine the nanomechanical properties of PMMA.

Fretting wear behaviour and frictional force mapping of Al2O3 based thermal barrier coatings

Efficiency and structural stability of gas-turbine engines were acheived with compliant thermal barrier coatings (TBCs) on structural components. In TBCs, top ceramic coatings encountered with other structural parts in a relative motion (amplitude of 100–500 μm and frequency of 1–5 Hz) was leading to failure, namely fretting wear. So, a high hardness material, Al2O3 based ceramic matrix composite (CMC) coatings were utilized to improve the tribological properties of the engineered surface. At this juncture, fretting wear behaviour of atmospheric plasma sprayed Al2O3–3 and 8 mol% Y2O3 stabilized ZrO2 (3YSZ and 8YSZ)‑carbon nanotube (CNT) based CMC coatings were investigated. The fretting wear rate of Al2O3 based CMC coatings against WC ball was observed as 0.97–1.87 × 10−6 mm3N−1 m−1. The least in wear resistance of Al2O3-CNT (1.87 × 10−6 mm3N−1 m−1) among the composite coating is attributed to low hardness and high Hertzian contact pressure (1.65 GPa) on the coatings. Among the composite coatings, Al2O3-3YSZ and Al2O3-8YSZ-CNT showed an improved wear resistance (~40.1% and ~34.5%, respectively) with wear rate of 0.97 × 10−6 mm3N−1 m−1 and 1.06 × 10−6 mm3N−1 m−1, respectively. It is attributed to improved mechanical properties, altered surface by reciprocating motion and the presence of wear debris, which reduces the wear rate by acting as a third body. So, there is an overestimation of wear rate (4.1–6.6 times) compared to that of experimentally calculated wear rate. Further, the Al2O3-YSZ-CNT composite showed fatigue crack on the fretting wear surface due to low plasticity index (62.0–109.3 MPa) of the coating. Also, the gradual change of running-in regime to the steady-state regime is achieved in the CNT reinforced composite coatings due to high resistance by the coatings which possess commendable mechanical properties. The frictional force mapping during the reciprocating motion confirms the rapid and gradual transition of two different regimes in the composite coatings.

Rate sensitivity and deformation mechanism of semi‐crystalline polymers during instrumented indentation

AbstractInstrumented indentation tests using both constant loading rate (CLR) and continuous stiffness measurement (CSM) operation modes were performed to investigate the deformation mechanism and their sensitivity to the deformation rate in semi‐crystalline polymers through the quantitative analysis of load‐depth loading and unloading curves. The strain rate was constant during the CSM tests, while the strain rate decreased with the increasing of loading time in CLR tests. The mechanical response mechanism of the semi‐crystalline polymers to these tests was very complicated because of the combined effects of strain‐hardening in the crystal phase and strain‐softening in the amorphous phase. Results show that the loading index m reflects the strain‐hardening or strain‐softening response during indentation. When m > 2, the mechanical response was due to the strain‐hardening, and when m < 2, the response was due to strain‐softening. A method based on the measured contact hardness was proposed to obtain the unloading stiffness, and the other mechanical parameters could then be determined according to the unloading stiffness.

Intrinsic properties of osteomalacia bone evaluated by nanoindentation and FTIRM analysis

Osteomalacia is a pathological bone condition consisting in a deficient primary mineralization of the matrix, leading to an accumulation of osteoid tissue and reduced bone mechanical strength. The amounts, properties and organization of bone constituents at tissue level, are known to influence its mechanical properties. It is then important to investigate the relationship between mechanical behavior and tissue composition at this scale in order to provide a better understanding of bone fragility mechanisms associates with this pathology.Our purpose was to analyze the links between ultra-structural properties and the mechanical behavior of this pathological bone tissue (osteomalacia) at tissue level (mineral and osteoid separately, or global). Four bone biopsies were taken from patients with osteomalacia, and subsequently embedded, sectioned, and polished. Then nanoindentation tests were performed to determine local elastic modulus E, contact hardness Hc and true hardness H for both mineralized and organic bone phases and for the global bone. The creep of the bone was also studied using a special indentation procedure in order to assess visco-elasto-plastic (creep) bone behavior. This allowed a detailed study of the rheological models adapted to the bone and to calculate the parameters associated to a Burgers model. Ultra-structural parameters were measured by Fourier Transform InfraRed Microspectroscopy (FTIRM) on the same position as the indents.The use of rheological models confirmed a significant contribution from the organic phase on the viscous character of bone tissue. The elastic E and the elasto-plastic Hc deformation were correlated to both collagen maturity and Mineral/Matrix. The pure plastic deformation H was only correlated to the mineral phase. Our data show that mineral phase greatly affects mechanical variables (moduli and viscosities) and that organic phase (as illustrated in osteoid tissue) may play an important role in the creep behavior of bone. In conclusion, this study brings mechanical and physicochemical values for osteoid and mineral phases.

The effects of turmeric on the grain structure and properties of copper electrodeposited composites

ABSTRACT The objective of this research was to electrocodeposit turmeric particles into copper matrices, and assess the influence of turmeric on the microstructure and properties of those deposits. The incorporation of turmeric had a significant effect on both the grain structure and properties of the copper deposits, with turmeric particles of a Z-average size of 289 ± 30 and 278 ± 15 nm having a greater influence on grain refinement than particles of 134 ± 37 nm, even at much lower deposit particle contents. The incorporated turmeric increased both the hardness and water contact angle of the deposits; however, a reduction in resistance to salt spray corrosion was also observed.

Creep correction of elastic modulus and hardness for viscoelastic materials during microindentation

In this paper, a dimensionless creep correction factor is proposed to simplify the calculation by using a fitting function of creep displacement combined with reduced modulus formula. Using experimental results of PA12 under different testing conditions during indentation, the creep‐corrected calculations of contact depth, reduced modulus, and hardness are studied. Results show that the elastic modulus without creep correction is significantly over‐estimated, while the creep‐corrected elastic modulus is a constant value (1.25 GPa) which does not change with the test variables. Conversely, the nanohardness extracted by the conventional approach is under‐estimated and the creep‐corrected contact hardness is not constant due to the time‐dependent deformation. The introduction of creep correction factor can significantly simplify the correction calculation process of material parameters.