Ball Indentation Hardness Research Articles

Effect of accelerated aging on the thermo-mechanical behavior and biotribological properties of an irradiation cross-linked GO/UHMWPE nanocomposite after VE diffusion.

In this work, the influence of accelerated aging on the thermo-mechanical behavior and biotribological properties of an irradiation cross-linked GO/UHMWPE nanocomposite after VE diffusion was investigated, including through differential scanning calorimetry (DSC), gel content, FT-IR characterization, oxidation index, ball indentation hardness, and especially the biotribological properties. The results show that accelerated aging increased the melting point and crystallinity of the nanocomposite, but resulted in a decrease in thermal stability and gel content. The oxidation index increased by 60.2% and the hardness decreased by 18.1%. In particular, the friction coefficient and wear rate increased by 99.5% and 87.4% respectively. A simple VE diffusion process had no obvious effect on the melting point, crystallinity, thermal stability, gel content and hardness, but the oxidation resistance and biotribological performance were improved to a certain extent. On the contrary, when VE exists in the accelerated aging process, the above properties are significantly improved. In particular, the oxidation index decreased by 21.1%, and the friction coefficient and wear rate decreased by 33.7% and 26.4%, respectively. After accelerated aging, fatigue wear and abrasive wear are the main wear forms, while VE plays the function of reducing friction and wear. Besides, the anti-friction and wear resistance mechanism of VE during the accelerated aging process was also illustrated.

Graphite Fluoride as a Novel Solider Lubricant Additive for Ultra-High-Molecular-Weight Polyethylene Composites with Excellent Tribological Properties

The tribological properties of ultra-high-molecular-weight polyethylene (UHMW-PE) play a significant role in artificial joint materials. Graphite fluoride (GrF), a novel solid lubricant, was incorporated into ultra-high-molecular-weight polyethylene (UHMW-PE) at different concentrations via ball milling and heat pressing to prepare the GrF-UHMW-PE composites. The structure, hardness, and tribological behavior of the composites were investigated using X-ray diffraction (XRD), Fourier-transform infrared (FT-IR) spectrometry, ball indentation hardness, and a reciprocating ball-on-plane friction tester, respectively. The results of FT-IR showed that hydrogen bonds (C-F···H-C) could be formed between GrF and UHMW-PE. The hardness of the composites was significantly enhanced by increasing the GrF concentrations. GrF in the composites displayed superior lubricant properties and the coefficient of friction (COF) of the composites was significantly decreased at lower concentrations of GrF viz. 0.1 and 0.5 wt%. The addition of GrF also significantly enhanced the anti-wear properties of the composites, which was a combined effect of lubrication as well as hardness provided by GrF. At 0.5 wt% GrF concentration, the COF and the wear rate were reduced by 34.76% and 47.72%, respectively, when compared to UHMW-PE. As the concentration of GrF increased, the wear modes of the composites transitioned from fatigue wear to abrasive wear. Our current work suggested that GrF-UHMW-PE composites could be a suitable candidate for artificial joint materials.

Effect of Candida albicans Suspension on the Mechanical Properties of Denture Base Acrylic Resin.

Yeast-like fungi such as Candida albicans (C. albicans) are the primary pathogenic microorganism in the oral cavity of denture wearers. The research available so far, conducted according to a protocol based on the exposure of specimens to a C. albicans suspension and their cutting with water cooling, shows that hard polymethyl methacrylate (PMMA) prosthetic materials are not only surface colonized, but also penetrated by microorganisms in a short time. This justifies the hypothesis that exposure to a suspension of the C. albicans strain causes the changes in mechanical properties due to surface colonization and/or penetration of the samples. In the current study, the chosen mechanical properties (flexural strength, flexural modulus, tensile strength, impact strength, ball indentation hardness, and surface Vickers hardness at 300 g load) of the PMMA denture base material Vertex RS (Vertex-Dental, The Netherlands) exposed for 30, 60, and 90 days to a suspension of C. albicans were investigated. The potential penetration of yeast was examined on the fractured surfaces (interior of specimens) to eliminate the risk of the contamination of samples during cutting. There was no influence on the flexural strength, flexural modulus, tensile strength, impact strength, or ball indentation hardness, but a significant decrease in surface hardness was registered. Microscopic observations did not confirm the penetration of C. albicans. On the surface, blastospores and pseudohyphae were observed in crystallized structures and in traces after grinding, which indicates that in clinical conditions, it is not penetration but the deterioration of surface quality, which may lead to the formation of microareas that are difficult to disinfect, causing rapid recolonization.

Study on the properation and properties of PP/mental aluminium power composites

In this paper, polypropylene(PP) was blended with aluminum powder, porous powder and EVOH reinforcing agent in different proportions by melt blending method. The infrared spectrum analysis of the blending components was carried out to study the tensile strength, impact strength, ball indentation hardness and heat resistance of the composites with different proportions. The results show that when the content of aluminum powder is 2 wt.%, the content of porous powder is 9 wt.%, and the content of EVOH is 4 wt.%, the heat resistance of the composite is the best. The tensile strength, impact strength and hardness of the composite are 21.33 MPa, 1.83 MPa and 74.78 N/mm 2, respectively. At this time, the composite has the best comprehensive properties.

GO 강화 및 조사 가교된 UHMWPE/VE 나노복합재료의 경도와 스크래치 저항의 증가

In this study, a way to reinforce the properties of ultrahigh molecular weight polyethylene (UHMWPE)/vitamin E (VE) nanocomposites was put to use by adding graphene oxide (GO) combined with gamma-ray irradiation cross-linking. The influences of adding GO and irradiation cross-linking treatment on the thermal and mechanical properties were studied, especially the effect of GO doping on irradiation cross-linked UHMWPE/VE nanocomposites. The results show that GO filling has no significant effect on melting temperature and gel content decreased at a small degree, but the crystallinity has been improved obviously. In addition, the ball indentation hardness and scratch resistance were enhanced as well. The comprehensive effects of improved crystallinity and reduced cross-linking degree as well as the good mechanical properties of GO doping were responsible for this result.

Oxidative degradation behavior of irradiated GO/UHMWPE nanocomposites immersed in simulated body fluid

In this study, the artificial joint substrate material of ultra-high molecular weight polyethylene (UHMWPE) is modified by irradiation cross-linking and graphene oxide (GO). The aim of the study is to evaluate the oxidative degradation behavior of GO/UHMWPE nanocomposites immersed in the simulated body fluid (SBF) atmosphere for a long term at 37 °C, using SBF absorption rate, Fourier transform infrared spectroscopy, electron spin resonance and ball indentation hardness. The results demonstrated that both methods of irradiation cross-linking and GO mixing can effectively improve the physicochemical properties and mechanical properties of UHMWPE matrix. After all the samples were immersed for 12 months, the value of ball indentation hardness of UHMWPE, R-UHMWPE, GO/UHMWPE and R-GO/UHMWPE was decreased by 19.6%, 23.18%, 34.58% and 31.88%, respectively. The GO/UHMWPE nanocomposites suffer from severe oxidative degradation compared to the original UHMWPE. Particularly, the pre-degradation rate was accelerated when mixed with GO. However, irradiated GO/UHMWPE (R-GO/UHMWPE) still exhibited optimal physical performance after oxidative degradation. This study highlights the importance of using more realistic solutions to characterize the performance of the modified UHMWPE nanocomposites, and reveals the mechanism of GO addition and irradiation cross-linking treatment on the UHMWPE nanocomposites immersed in SBF for a long time.

Development of polylactide composites with improved thermomechanical properties by simultaneous use of basalt powder and a nucleating agent

AbstractIn the course of the study, polylactide (PLA)/basalt powder (BP) composites were fabricated, incorporating micrometric particle‐shaped waste filler into the biodegradable polyester matrix to obtain improved thermomechanical stability of the final products. The mechanical, thermomechanical, and thermal properties of PLA‐based composites were evaluated, accounting for the influence of the simultaneous incorporation of 1 wt% of the potassium salt of 3,5‐bis(methoxycarbonyl) benzenesulfonate (LAK) used as the nucleating agent and 5‐20 wt% of basalt powder. As each of the applied modifying agents improves the thermomechanical stability of PLA, a beneficial effect of the co‐modification on thermal properties was expected to widen the temperature range of application of the composites. Differential scanning calorimetry measurements showed an increase of crystallinity up to 55% in the case addition of both additives (BP and LAK) on the PLA. The thermomechanical stability of the composites was determined as a heat deflection temperature (HDT) test. High modification efficiency of BP was obtained only with the simultaneous addition of the LAK nucleating agent. The synergistic effect of both modifiers allowed us to achieve a more than 100% increase in the HDT value to almost 160°C. The mechanical properties were assessed by the static tensile test, Dynstat impact measurements, and a ball indentation hardness evaluation. Even though a 10 MPa decrease in tensile strength was observed due to the addition of 20 wt% of BP and 1% of LAK, the tensile modulus increased from 2.5 to 3.25 MPa and hardness rose from 140 to 175 MPa. The addition of 5 wt% of basalt powder caused a 2 kJ/m2 increase in impact strength. The modification of PLA with the filler and the nucleating agent improved not only thermal stability but also the mechanical properties of the material.

Study on the reinforcing effect of nano-SiO2 filled PTFE composites

The wear behavior and coefficient of friction for Nano-SiO2 filled polytetrafluoroethylene (PTFE) was investigated under dry conditions. The ball indentation hardness, tensile strength and elongation at break were determined. It was found that both ball indentation hardness and tensile properties were better reinforced by nano-SiO2 particles. The tribological properties of the nano-SiO2 PTFE composite and the regular SiO2 PTFE composite were compared for several applied loads. The worn surfaces were examined by means of scanning electron microscopy (SEM) and 3D profilometry. It was determined that the wear rate of PTFE composites filled with Nano-SiO2 particles considerably decreased. The friction forces were found to be lower for the Nano-SiO2 filled composites than those in the regular particles composite for the same experimental conditions.

Influence of Five-Year Degradation on Mechanical and Tribology Properties of Ultra-High-Molecular-Weight Polyethylene

ABSTRACTUltra-high-molecular-weight polyethylene (UHMWPE) has been the most commonly used bearing material in total joint replacement. The degradation of UHMWPE components has a notable influence on its mechanical properties. UHMWPE samples were immersed in simulated fluid (SBF) up to 5 years and the change in chemical composition and mechanical and wetting properties was investigated. It was found that the oxygen/carbon (O/C) ratio and crystallinity increased from 14.5 and 50.0% before immersion to 52.8 and 60.7% after immersion in SBF for 5 years, respectively. These resulted in a reduction in ball indentation hardness, scratch coefficient, peak load, and contact angle by 35.7, 21.0, 15.8, and 14.0%, respectively, after 5 years of immersion. The steady-state friction coefficient and wear rate increased 83.3 and 43.8%, respectively, after immersion in SBF for 5 years. The preliminary study indicated that the scratch test was an effective method to evaluate the surface performance of UHMWPE after short-term degradation, and small punch test was often used to assess the bulk properties of UHMWPE after long-term degradation.

Processing and Mechanical Properties of Ultra-high Molecular Weight Polyethylene Reinforced by Silver Nanoparticles

The present study was designed to investigate the mechanical performance of ultra high molecular weight polyethylene (UHMWPE) reinforced by silver nanoparticles. The Ag/UHMWPE nanocomposites were prepared by a plate vulcanizing machine and tested with a contact angle micrometer, UMT friction tester, electronic universal testing machine and MicroXAM three-dimensional profilometer to characterise the wettability, ball indentation hardness, creep resistance, compression properties, and friction and wear performance. A scanning electron microscope (SEM) was employed to describe the morphology of the Ag/UHMWPE nanocomposites surfaces following the friction and wear tests. These results demonstrate that the compressive yield strength, ball indentation hardness and creep resistance increased with an increase in the content of silver nanoparticles. The contact angle of the Ag/UHMWPE nanocomposites with bovine calf serum decreases with an increase in the content of silver nanoparticles and this change increases the wettability of the Ag/UHMWPE nanocomposites. Therefore, the friction coefficient decreases, but the wear mechanism changes from scratch and furrow to fatigue flakes when the mass fraction of silver nanoparticles exceeds 0.3%. The composite with a silver nanoparticles mass fraction of 0.3% exhibits a low friction coefficient and good wear resistance.

Determination of the Mechanical Properties of Epoxy Silica Nanocomposites through FEA-Supported Evaluation of Ball Indentation Test Results

In the present paper a continuous Finite Element Analysis (FEA) simulation method of the ball indentation hardness test is introduced in order to describe the deformation behavior of nanosilica composites and with this to extract precisely the material's stress-strain behavior. The developed procedure demonstrate in particular the adequacy of this method to determine the nanocomposites' elastic modulus which is compared with Halpin-Tsai and Lewis-Nielsen models as well as with experimental measurements taken from uniaxial tensile tests. The fracture area of all the tensile specimens was examined using a scanning electron microscope (SEM). It is shown that the correlation between the experimental results, the semi-empirical models and the FEA computational models concerning the elastic modulus values was satisfactory with very small deviations.

Evaluation of highly filled epoxy composites modified with walnut shell waste filler

Epoxy composites modified with ground walnut shell used as organic waste fillers were prepared and examined. Post-agricultural waste materials after grinding were characterized by evaluation of grain size distribution and structure observations realized using scanning electron microscope (SEM). The influence of filler addition on the mechanical properties of epoxy-based composites was determined by: static tensile test, Charpy impact test, and ball indentation hardness measurements. Composite samples containing 20, 30, 40, and 50 wt% of walnut shell were characterized by increased stiffness and hardness in comparison to the unmodified resins. Moreover, the incorporation of the filler resulted in a decrease of composite material tensile strength and impact resistance. Thermo-mechanical properties of the composites were investigated by dynamic mechanical thermal analysis (DMTA). Results obtained from DMTA tests showed a growth in the composites’ stiffness at elevated temperatures as a function of the increasing natural filler content. The material characterization was supplemented by thermal stability evaluation realized by thermogravimetric analysis (TGA). It was found that the incorporation of ground walnut shell led to an improved thermal stability of composite materials. The analysis of the change in composite material properties, caused by natural filler incorporation, was complemented by material microstructure observations.

Mechanical properties study of micro‐ and nano‐hydroxyapatite reinforced ultrahigh molecular weight polyethylene composites

ABSTRACTThis is a comparative study between ultrahigh molecular weight polyethylene (UHMWPE) reinforced with micro‐ and nano‐hydroxyapatite (HA) under different filler content. The micro‐ and nano‐HA/UHMWPE composites were prepared by hot‐pressing method, and then compression strength, ball indentation hardness, creep resistance, friction, and wear properties were investigated. To explore mechanisms of these properties, differential scanning calorimetry, infrared spectrum, wettability, and scanning electron microscopy with energy dispersive spectrometry analysis were carried out on the samples. The results demonstrated that UHMWPE reinforced with micro‐ and nano‐HA would improve the ball indentation hardness, compression strength, creep resistance, wettability, and wear behavior. The mechanical properties for both micro‐ and nano‐HA/UHMWPE composites were comparable with pure UHMWPE. The mechanical properties of nano‐HA/UHMWPE composites are better compared with micro‐HA/UHMWPE composites and pure UHMWPE. The optimum filler quantity of micro‐ and nano‐HA/UHMWPE composites is found to be at 15 wt % and 10 wt %, separately. The micro‐ and nano‐HA/UHMWPE composites exhibit a low friction coefficient and good wear resistance at this content. The worn surface of HA/UHMWPE composites shows the wear mechanisms changed from furrow and scratch to surface rupture and delamination when the weight percent of micro‐ and nano‐HA exceed 15 wt % and 10 wt %. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 42869.

Mechanical Properties and Tribological Behaviour of Retrieved Uhmwpe Tibial Insert in Total Knee Replacement after Implantation 30 Months

This study was performed to investigate the performance changing of an ultra high molecular weight polyethylene (UHMWPE) tibial insert, which was removed from a 56 years old male patient after 30 months of service. The tibial insert was investigated by using a contact angle goniometer, UMT-2 friction tester and MicroXAM three-dimensional profilometer to characterize the wettability, ball indentation hardness, creep resistance, friction and wear performance. Scanning electron microscopy (SEM) was employed to describe the morphology of the sample surface of unused and retrieved UHMWPE after friction and wear test. Surface differential scanning calorimetry (DSC) was used to calculate the surface crystallinity of UHMWPE. The results showed that the contact angle of retrieved UHMWPE with bovine calf serum was obviously decreased by about 15% compared with unused UHMWPE. The surface crystallinity of retrieved UHMWPE increased 9.6% compared with unused UHMWPE. All of these induced the ball indentation hardness and creep resistance decreased 18% and 31%, the wear loss of retrieved UHMWPE increased 24% compared with unused UHMWPE.

A new generation of testing machine: Recording macroindentation techniques for fast assessment of temperature-dependent material properties

The authors introduce a prototype of a recording (depth-sensing) macroindentation testing machine that has been modified and extended with a temperature chamber. This prototype allows the analysis of different hardness values (Martens hardness, indentation hardness, ball indentation hardness, etc.) and the indentation modulus, as well as time-dependent properties such as creep and relaxation of polymers and other materials, in a wide range of temperature (−100 – 100 °C). The applicability of the testing machine for fast and less material-consuming determination of the temperature-dependent mechanical properties is illustrated by means of selected amorphous and semicrystalline thermoplastics, i.e., neat (PMMA and PTFE) and reinforced ones (PMMA/silica nanocomposites).

Tribological behavior of poly (phenyl p-hydroxybenzoate)/polytetrafluoroethylene composites filled with hexagonal boron nitride under dry sliding condition

The sliding friction and wear behavior of polytetrafluoroethylene (PTFE) composites filled with poly (phenyl p-hydroxybenzoate) (PHBA) and hexagonal boron nitride (h-BN) was investigated with a pin-on-disc tester. The tensile properties, ball indentation hardness, impact strength and thermal diffusivity were measured. The test results in this paper indicate that the tensile strength, elongation at break, and impact strength decreased, however, the ball indentation hardness and thermal diffusivity were increased when the content of h-BN was increased. PTFE composites filled with 20wt% PHBA and 20wt% h-BN exhibited a comparative friction coefficient to pure PTFE. Meantime, the wear rate of the composite decreased about 15 times compared to pure PTFE. The synergistic effect of h-BN with low friction and PHBA with high bearing ability promoted the low friction coefficient and wear rate of h-BN/PHBA/PTFE composites.

Mechanical and Tribological Properties of PTFE Composites Filled with POB

The POB/PTFE composites were prepared by blending-cold pressing-sintering-hot pressing method. Influence of POB content on mechanical and tribological properties of the composites was investigated. Worn surfaces were analyzed by scanning electron microscope (SEM). The results indicated that ball indentation hardness and compressive strength of POB/PTFE increase with increasing POB content in composites. Tensile strength, elongation and impact strength of POB/PTFE decrease with increasing POB content in composites. Friction coefficient of composites increases compared to PTFE. Wear resistance of POB/PTFE composites was improved with filling POB. The POB/PTFE composite incorporating 20% POB has best comprehensive mechanical properties. Wear mechanism of PTFE are abrasive wear. Wear mechanism of POB/PTFE composites mainly are fatigue wear and flaking.

Metallurgical characterization of refrigeration tubing formed from plain carbon steel strip stock

Ball indentation hardness testing and metallography were used to investigate the metallurgical changes that occur during the manufacture and bending of plain carbon steel tubing for use in large-scale refrigeration equipment such as evaporative condensers and thermal storage coils. A significant increase in hardness occurred in going from flat strip starting material to creating the electrical resistance welded tubing that was subsequently bent to form coils. The weld region exhibited the greatest hardness. Metallographic examination revealed that the spheroidized ferritic microstructure of the flat strip was retained during welding. However, the accompanying heating did cause small grains to form and a significant rise in the number of carbide particles.

Reciprocating Triboligical Behavior of PA1010 Filled with ZnOw

The friction and wear behavior of nylon1010 composites filled with different proportions of ZnOw in reciprocating sliding against GCr15 steel ball under dry friction condition were studied. The worn surface and wear particles were then examined with SEM. The elastic modulus, nano-hardness and ball indentation hardness of composites increased with the content of ZnOw. The coefficients of friction of composites decreased lightly, which changed from 0.36 and 0.26 of nylon matrix to 0.30 and 0.22 of composites at 0.04 m/s and 0.08m/s sliding velocity, respectively. The anti-wear property of composites was improved with large extent. The typical wear mechanism of nylon matrix is adhesion and micro-melting. However, peeling of surface layer appears owing to fatigue for composites. Roll-shaped wear debris were produced for pure nylon, while flake-like debris for nylon composites.

Meyer's hardness law and its relation to other measures of ball hardness tests

AbstractThe force dependence of the ball indentation hardness can be described in many cases by MEYER's hardness law. The characteristic material parameters are the MEYER constant K and the MEYER exponent n. But often other simple measures of hardness are used for technical applications. Examples are the difference of hardness for two different loads, which gives a good view of the hardening capability of the material, and the BRINELL hardness.It is shown that empirical found relations between the mentioned measures of hardness and the MEYER parameters are strong consequences of the validity of MEYER'S law. In special ranges of the values of the material parameters these empirical relations are linear ones. As a result of the theoretical considerations one must recommend to use the theoretical relations to fit the experimental values, because only in this case all physical conditions are fulfiled automatically.