Mechanical properties of silicate glass–ceramics containing tricalcium phosphate

The flexural strength, elastic moduli, Vickers hardness and fracture toughness for silicate glass-ceramics (anorthite and diopside) containing tricalcium phosphate (TCP) were measured. The microstructures of the silicate glass–ceramics containing TCP were shown to consist of a complex structure of rod-like silicate and TCP crystals. The flexural strengths of glass–ceramics containing 32 wt% TCP for anorthite and 38 wt% TCP for diopside corresponding to a eutectic composition in the phase diagram were 236 and 226 MPa. The Youngs modulus and fracture toughness of the eutectic compositions were 89.4 GPa and 2.5 MPa·m1/2 for anorthite and 126 GPa and 2.3 MPa·m1/2 for diopside, respectively. The anorthite glass–ceramic containing TCP has a lower Youngs modulus in spite of a high strength as compared to other silicate glass–ceramics containing apatite or TCP.     

Stoichiometry of hydroxyapatite: influence on the flexural strength

This paper reports results on the sintering behaviour of hydroxyapatite (HAP) for various compositions and its resultant flexural strength. The HAP decomposition occurs at higher temperatures for sintered compacts than for powder and their OH stoichiometry depends on the porosity-closing temperature. The mechanical behaviour of HAP depends on its composition: the best results are obtained for HAP containing tricalcium phosphate (TCP), whereas for nearly pure HAP the flexural strength decreases to the lowest results corresponding to HAP containing CaO. It is suggested that the strengthening of HAP by TCP involves surface compression due to the TCP transformation.     

Fabrication and characterization of hydroxyapatite reinforced with 20 vol % Ti particles for use as hard tissue replacement

Hydroxyapatite(HA)-based composite reinforced with 20 vol % titanium (Ti) particles was fabricated by hot pressing based on the studies of the structural stability of HA phase in HA–Ti composite by means of FTIR spectrometry and X-ray diffractometry. The mechanical properties and biological behaviors of the composite were investigated by mechanical and in vivo studies. The existence of Ti metal phase can promote the dehydration and decomposition of HA ceramic phase into the more stable calcium phosphate phases, such as –Ca₃(PO₄)₂ (–TCP) and Ca₄O(PO₄)₂ at high temperatures. Comparing with pure HA ceramic manufactured under the same conditions, HA–20 vol % Ti composite with higher fracture toughness (0.987 MPa m^1/2), bending strength (78.59 MPa), work of fracture (12.8J/m²), porosity (9.8%) and lower elastic modulus (75.91 GPa) is more suitable for use as hard tissue replacement. Crack deflection is the chief toughening mechanism in the composite. Histological evaluation by light microscope shows HA–20 vol % Ti composite implant could be partially integrated with newborn bone tissues after 3 weeks and fully osteointegrated at 12 weeks in vivo. The excellent biological properties of HA–20 vol % Ti composite may be contributed to the coexistence of high porosity and the decomposition products of HA phase in the composite.     

Microstructures and room temperature mechanical properties of NiAl prepared by high pressure reaction sintering

The microstructures and room temperature compressive mechanical properties of a nearstoichiometric NiAl manufactured by a new high pressure reaction sintering (HPRS) process are investigated. Applying a very high uniaxial pressure (2 GPa) leads to considerable lowering of the sintering temperature and reducing the hold time gives NiAl with a good sintering density. The HPRS NiAl consists of -NiAl with a B2 structure containing a high density of dislocations, 3.5×10⁹ cm^–2, and very fine Al₂O₃ particles. The NiAl exhibits quite high true compressive strain, 14.5%, and a reasonably high yield strength, 526 MPa. The effects of employing the high pressure in the HPRS process on the reaction sintering, microstructures and mechanical properties of the NiAl are studied.     

纳米羟基磷灰石/聚酰胺6医用复合材料的制备及性能表征

为防止纳米羟基磷灰石(nano HAP)粉末的团聚,采用溶剂沉淀法制备了nano HAP/聚酰胺6(PA6)复合粉末,并对粉末进行热压成型制得nano HAP/PA6复合材料。然后,通过FTIR、XRD和SEM对nano HAP/PA6复合材料的成分、结构和形貌进行了表征,并对复合材料的热稳定性、力学性能和细胞相容性进行了检测。结果表明:所制备的nano HAP/PA6复合材料结晶体大小均匀,且PA6只存在α型结晶;由于nano HAP与PA6界面上形成新的氢键和COO—Ca,复合材料具有良好的综合性能;在低于350℃时,nano HAP/PA6复合材料不会发生裂解,力学性能与人骨匹配,50wt%nano HAP/PA6复合材料的弯曲强度、压缩强度和弹性模量分别为146.87MPa、98.44MPa和5.44GPa。MG-63骨瘤细胞在nano HAP/PA6复合材料表面粘附和生长状况良好,说明nano HAP/PA6复合材料具有良好的细胞相容性。所得结论表明nano HAP/PA6复合材料在骨修复方面具有应用价值。     

Immunohistochemical evaluation after Sr-enriched biphasic ceramic implantation in rabbits femoral neck: comparison of seven different bone conditions

Strontium (Sr) has shown effectiveness for stimulating bone remodeling. Nevertheless, the exact therapeutic values are not established yet. Authors hypothesized that local application of Sr-enriched ceramics would enhance bone remodeling in constant osteoporosis of rabbits’ femoral neck bone. Seven different bone conditions were analyzed: ten healthy rabbits composed a control group, while other twenty underwent ovariectomy and were divided into three groups. Bone defect was filled with hydroxyapatite 30% (HAP) and tricalcium phosphate 70% (TCP) granules in 7 rabbits, 5% of Sr-enriched HAP/TCP granules in 7, but sham defect was left unfilled in 6 rabbits. Bone samples were obtained from operated and non-operated legs 12 weeks after surgery and analyzed by histomorphometry and immunohistochemistry (IMH). Mean trabecular bone area in control group was 0.393 mm2, in HAP/TCP – 0.226 mm2, in HAP/TCP/Sr – 0.234 mm2 and after sham surgery – 0.242 mm2. IMH revealed that HAP/TCP/Sr induced most noticeable increase of nuclear factor kappa beta 105 (NFkB 105), osteoprotegerin (OPG), osteocalcin (OC), bone morphogenetic protein 2/4 (BMP 2/4), collagen type 1α (COL-1α), interleukin 1 (IL-1) with comparison to intact leg; NFkB 105 and OPG rather than pure HAP/TCP or sham bone. We concluded that Sr-enriched biomaterials induce higher potential to improve bone regeneration than pure bioceramics in constant osteoporosis of femoral neck bone. Further studies on bigger osteoporotic animals using Sr-substituted orthopedic implants for femoral neck fixation should be performed to confirm valuable role in local treatment of osteoporotic femoral neck fractures in humans.

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Mechanical characterization of dense calcium phosphate bioceramics with interconnected porosity

Porous hydroxyapatite/tricalcium phosphate (HA/TCP) bioceramics were fabricated by a novel technique of vacuum impregnation of reticulated polymeric foams with ceramic slip. The samples had approximately 5–10% interconnected porosity and controlled pore sizes appropriate to allow bone ingrowth, combined with good mechanical properties. A range of polyurethane foams with 20, 30 and 45 pores per inch (ppi) were used as templates to produce samples for testing. The foams were inpregnated with solid loadings in the range of 60–140 wt%. The results indicated that the average apparent density of the HA/TCP samples was 2.48 g/cm³, the four-point bending strength averaged 16.98 MPa, the work of fracture averaged 15.46 J/m² and the average compressive strength was 105.56 MPa. A range of mechanical properties resulted from the various combinations of different grades of PU foam and the solid loading of slips. The results indicated that it is possible to manufacture open pore HA/TCP bioceramics, with compressive strengths comparable to human bone, which could be of significant clinical interest.     

A tough nut to crack

A study of the microstructure and mechanical properties of macadamia nutshells reveals these to behave like an isotropic wood. Their dry density is 1.3×10³kgm^–3, their Vickers hardness is 180±30 MPa, their fracture strength is 25 to 80 MPa and their fracture toughness is 1 to 2MPam^1/2. Their Young's modulus probably lies nearer the highest (6GPa) than the lowest (2GPa) of the present measurements and their work of fracture lies in the range 100 to 1000 Jm^–2. None of the mechanical properties is obviously dependent on the water content of the shell. The results demonstrate quantitatively why these shells have a reputation for being difficult to crack.     

Mechanical and biological properties of hydroxyapatite reinforced with 40 vol. % titanium particles for use as hard tissue replacement

Hydroxyapatite (HA)-based composite reinforced with 40 vol. % Ti particles was fabricated by the optimal technical condition of hot pressing technique. The mechanical and biological properties of the composite were studied by mechanical and in vivo methods. The experimental results show that HA and Ti phases are the predominant phases of the composite with partially decomposition of HA phase into -Ca₃(PO₄)₂ and Ca₄O(PO₄)₂. Comparing with HA–20 vol. % Ti composite manufactured under the same conditions, HA–40 vol. % Ti composite with similar elastic modulus (79.3 GPa) and Vicker's hardness (2.94 GPa) has a higher bending strength (92.1 MPa). Moreover, fracture toughness of HA–40 vol. % Ti composite with crack bridging as the chief toughening mechanisms can reach 2.692 MPa m^–1, which can meet the basic toughness demand of the replaced hard tissues for heavy load-bearing applications. Work of fracture of HA–40 vol. % Ti composite is 91.2 J m², which is 22.9 times that of pure HA ceramic and even 2.4 times that of Al₂O₃ bioceramic. The results of in vivo studies show HA–40 vol. % Ti composite has excellent biocompatibility and could integrate with bone. In the early stage after the implantation of the samples, the osteointegration ability of the composite is better than that of pure titanium.     

Effect of residual stresses on mechanical properties and interface adhesion strength of SiN thin films

Residual stresses play a significant role in the mechanical reliability of thin films. Thus in this study, the mechanical properties and interface adhesion strengths of SiN thin films containing different residual stresses have been investigated by using nanoindentation and nanoscratch tests. With varied residual stresses from compressive to tensile, the penetration depth of nanoindentation tests shifted to a higher value. The hardness and elastic modulus decreased from 11.0 and 95 GPa, respectively, for the film containing a compressive stress of 235 MPa to 9.6 and 84 GPa for the film with a tensile stress of 86 MPa. With decreasing compressive stress and increasing tensile stress, the interface adhesion energy decreased from 1.8 to 1.5 J/m². Compressive stresses were expected to blunt crack tips and inhibit crack propagation, while tensile stresses enlarged crack opening and facilitated crack propagation, thus changing the mechanical properties of the SiN thin films.     

Effect of a low-intensity pulse load on the mechanical characteristics of steels 20 and 12Kh18N10T

Variation in the mechanical characteristics of steels 20 and 12Kh18N10T is indicated from the results of the quasistatic uniaxial tensile testing of flat proportionally short specimens fabricated from thick-walled plates treated under a pressure pulse to 2 GPa with a duration to 10 sec. In calculating the mechanical characteristics, a cross section in the form of a curvilinear trapezium was replaced by a rectangle of equivalent area. It is established that the variation in the mechanical properties depends on the magnitude of the compressive strain generated under a pulsed load over the thickness of the plates. Tension diagrams from which it follows that the yield point and ultimate strength increase, and the relative elongation after failure decreases with increasing preliminary pulsed compressive deformation, are presented. The yield site that exists on the tension diagram of steel 20 specimens in the as-delivered state vanishes after shock treatment. The characteristic feature of a sharp (by 30%) increase in the yield point of steel 12Kh18N10T is observed on attainment of a small (to 1%) pulse deformation, with whose increase the relative necking after failure of both metals investigated diminishes somewhat.Translated from Problemy Prochnosti, No. 1, pp. 23–27, January, 1992.     

Mechanical characterization of Ni1−xZnxFe2O4 prepared by non-conventional methods

The mechanical properties like hardness, H_v and compressive strength, σ of Ni_1−xZn_xFe₂O₄ (x = 0.2, 0.3, 0.4 and 0.5) prepared by the non-conventional flash combustion and citrate-gel decomposition techniques are studied and reported. It is observed that there is an increase in hardness with zinc content as well as sintering temperature. The hardness in the order of 2.0–3.63 GPa and compressive strength in the order of 150–240 MPa are obtained for Ni–Zn ferrites prepared by these non-conventional techniques. The influence of density, porosity and microstructure on hardness and compressive strength of Ni–Zn ferrites with respect to sintering temperature was studied.     

The Measurement of Compressive Creep Deformation and Damage Mechanisms in a Single-Phase Alumina Part I Grain boundary sliding

Grain boundary sliding (GBS) has been hypothesized to act as the primary driving force for the nucleation and growth of grain boundary cavities in ceramics undergoing creep. In addition, GBS is often a major mode of deformation during high-temperature creep. This paper demonstrates the importance of GBS with mode II GBS measurements performed using a stereoimaging technique on a single-phase alumina tested under constant compressive stresses of 70 and 140 MPa at 1600 °C. Measurements were taken at constant time intervals during creep. The results support previous observations that GBS is stochastic and history independent. GBS displacements at given time intervals are shown to fit a Wiebull distribution. During steady-state creep, GBS displacements increased linearly with time at a constant sliding rate of 6.0 × 10–5 m s–1 at 70 MPa and 1.3 × 10–4 m s–1 at 140 MPa. Also, an average of 67% of the grain boundaries exhibited measurable sliding throughout the creep life of the 140 MPa test. Results of the GBS measurements are used to modify an existing creep model describing stochastic GBS. In part II of this paper [1], the GBS measurements reported are related to the associated creep cavitation measured in specimens tested under identical conditions.     

Fabrication of porous NiTi-shape memory alloy objects by partially hydrided titanium powder for biomedical applications

Porous NiTi-shape memory alloy (SMA) is a promising biomaterial with desirable mechanical property and appropriate biocompatibility for human implant manufacturing. In this research, porous NiTi-SMAs have been successfully produced by using thermohydrogen process (THP). This process has capability of production of homogenous structures, appropriate pore-size distributions and short sintering times. The THP-SMA samples produced in this research have a low Young’s modulus (19.8 GPa) and a high tensile strength of 255 MPa. These properties are close to those of the natural bone and can meet the mechanical property demands of the hard-tissue implants for heavy load-bearing applications. The samples produced exhibit sufficient thermoelastic effect distinguished by a 1.2% mean recoverable strain.     

Combustion synthesis and mechanical properties of molybdenum disilicide composites reinforced with SiC particulate

Intermetallic composites of molybdenum disilicide reinforced with silicon carbide were produced by combustion synthesis of the elemental powders. The combustion reaction was initiated near 700°C and completed within a few seconds. The end product was a porous composite which was subsequently hot pressed to >97% theoretical density. The grains of the matrix were 8–14 m in size surrounded by SiC particulate reinforcement of 1–5 m. The mechanical properties of the composites improved with increasing SiC reinforcement. The hardness of the materials increased from 10.1 GPa to 12.7 GPa with the addition of 20 vol% SiC reinforcement, while the strength increased from 195 MPa to 299 MPa. The fracture toughness also increased from 2.79 MPa m1/2 to 4.08 MPa m1/2 with 20 vol% SiC. © 1998 Chapman & Hall     

Mechanical behaviour of polycrystalline BeO,Al2O3 and AlN at high pressure

The mechanical behaviour of various types of BeO, Al₂O₃, and AlN have been investigated at confining pressures up to 1.25 GPa, at 25° C, and at strain rates of 3 to 7×10^–5 sec^–1. The stress-strain data taken in uniaxial compressive-stress loading indicate the BeO aggregates undergo a transition from brittle fracture at low pressures to plastic flow at high pressures. Depending on the fabrication process, this transition pressure in BeO occurs at 0.4 to 0.7 GPa. Concurrently, the ultimate compressive strength of BeO increases from 1.0 to 1.9 GPa at 0.1 MPa pressure to over 4.0 GPa at 1.O GPa. Alumina remains brittle at all pressures up to 1.25 GPa; its strength increases from 4.5 GPa at 0.1 MPa pressure to over 6.0 GPa at 1.25 GPa. Aluminium nitride behaves similarly to BeO, having a brittle-ductile transition at 0.55 GPa. Its ultimate strength increases from 3.2 GPa at 0.1 MPa pressure to 4.7 GPa at 0.8 GPa. The distortional strain energy (proportional to the area under the stress-strain curve) absorbed by each material during compression at pressure was calculated and compared to available data from the literature. Alumina shows a degraded energy absorption with pressure, but both BeO and AlN yield a strongly enhanced performance at moderate pressures. Beryllium oxide and AlN thus appear to be promising structural materials for certain applications where high strengths and ductilities are required at moderate pressures.     

Fabrication of porous titanium implants with biomechanical compatibility

By using H₂O₂ as foaming reagent, porous titanium with open and interconnected pore morphology was obtained. The morphology, pore structure and elemental composition were observed by SEM–EDX. The mechanical property was determined by compressive test. The results show that the compressive strength and Young's modulus of porous titanium with 64% porosity were 102 ± 10 MPa and 3.3 ± 0.8 GPa, respectively, and for 76% porosity porous titanium, the values were 23 ± 10 MPa and 2.1 ± 0.5 GPa. These results suggest that the former has sufficient mechanical properties for clinical use under load-bearing conditions and the latter has the potential application for tissue engineering scaffolds.     

Influence of the cross section shape on the behaviour of SRG-confined prismatic concrete specimens

The effectiveness of the steel-reinforced grout (SRG) jacketing technique in increasing both strength and deformation capacity has been substantiated by experimental evidence (Thermou and Pantazopoulou in Fib Struct Concr J 8: 35–46, 2007; Thermou et al. in ECCOMAS Thematic Conference, 2013; Thermou et al. in Mater Struct J, 2013). What it has not been addressed yet is the influence of the cross section shape on the behaviour of SRG-confined prismatic unreinforced concrete specimens. An experimental study was carried out where 18 concrete small scale specimens were tested to failure under concentric uniaxial compression load. A single layer of the steel-reinforced fabric was applied to circular, square and square specimens with rounded edges. Test results demonstrated that both strength and deformation capacity increased as the shape of the cross section changed from square to circular. In case of the square specimens, the gain in compressive strength was satisfying, whereas the ductility increase was more significant compared to that of the square specimens with rounded edges. An analytical expression for the lateral confining pressure exerted by the composite system was derived based on the assumption that the steel cords were treated as well-anchored steel stirrups placed at a distance equal to the spacing between the steel cords. The ability of the various steel and fiber-reinforced polymer confinement models from literature to predict the normalized compressive strength of non-circular specimens confined with SRG jackets was also explored.     

纳米羟基磷灰石形貌对复合材料力学强度的影响

采用不同形貌的羟基磷灰石纳米粒子与聚酸酐材料复合,研究了羟基磷灰石形貌对复合材料力学强度的影响,并用扫描电子显微镜观察了复合材料的断面形态.结果发现羟基磷灰石的形貌对材料的压缩强度和压缩弹性模量影响较大:长针状羟基磷灰石增强效果较好,所得复合材料的压缩强度可达256MPa,压缩弹性模量可达9.8GPa;片状羟基磷灰石的复合材料力学强度较差,压缩强度最高只有160Mpa,压缩弹性模量最高只有7.9GPa.     

Preparation and characterization of a novel bioactive bone cement: Glass based nanoscale hydroxyapatite bone cement

A novel type of glass-based nanoscale hydorxypatite (HAP) bioactive bone cement (designed as GBNHAPC) was synthesized by adding nanoscale hydroxyapatite (HAP) crystalline (20–40 nm), into the self-setting glass-based bone cement (GBC). The inhibition rate of nanoscale HAP and micron HAP on osteosarcoma U2-OS cells was examined. The effects of nanoscale HAP on the crystal phase, microstructure and compressive strength of GBNHAPC were studied respectively. It was concluded that nanoscale HAP could inhibit the cell proliferation, while micron HAP could not, and that nanoscale HAP could be dispersed in the cement evenly and the morphology did not change significantly after a longer immersion time. XRD and FTIR results show nanoscale HAP did not affect the setting reaction of the cement. Furthermore, GBNHAPC had a higher compressive strength (92 MPa) than GBC. It was believed that GBNHAPC might be a desirable biomaterial that could not only fill bone defects but also inhibit cancer cell growth.