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Results for “Compressive Strength”

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At least 811 records · Page 45Linked to original sources

PubMed1996

Mechanical properties of glass ionomers under static and dynamic loading.

OBJECTIVES: This study evaluated the mechanical properties under static and cyclic loading conditions of various types of glass ionomers used for bases and core build-ups under restorations. METHODS: Compressive strength and three-point flexural strength of two different glass ionomers and two metal-reinforced glass ionomers were determined 1 d after the start of mixing. The flexural fatigue resistance of these materials was measured in the load range of 650 g to 1050 g using a three-point bending machine, and fractured surfaces of the specimens were examined using SEM. RESULTS: All the glass ionomers exhibited similar compressive and flexural strengths. The results analyzed by Cox' proportional hazard model demonstrated that the admixed-type metal-reinforced glass ionomer had the highest fatigue resistance, while the water-hardening glass ionomer had the lowest fatigue resistance among the materials examined (p<0.5). SIGNIFICANCE: There was no significant improvement in the static mechanical properties from incorporating metal particles into the glass ionomers. However, the addition of metal particles as in the admixed-type metal-reinforced glass ionomer produced a material with increased fatigue resistance.

Cermet Cements↗

PubMed1995

Modified polyalkenoate (glass-ionomer) cement--a study.

Conventional glass-ionomer cements with varying amounts (5-15%) of borax (Na2B4O7.10H2O) as modifier were prepared. These mixtures were spatulated with an aqueous solution of polyacrylic acid with a powder to liquid (P/L) ratio of 1.5:1. Properties such as working time, setting time, compressive strength, diametral tensile strength, solubility and fluoride release of these cements were determined. It was observed that the working time and setting time of the resultant cements shortened with the addition of borax. Certain physical properties such as compressive and diametral tensile strength, solubility and disintegration of these glass-ionomer cements deteriorated with borax addition but fluoride release from them was unaffected.

Acrylic Resins↗

PubMed2004

Influence of aggregate pre-wetting and fly ash on mechanical properties of lightweight concrete.

This study has examined the mechanical properties of lightweight aggregate concrete with a density of 1800 kg/m3. The effects of the following parameters on the concrete properties have been analyzed: the pre-wetting time of the lightweight aggregate and the percentage of pulverized fly ash used as cementitious replacement material. The strength of the lightweight aggregate was found to be the primary factor controlling the strength of high-strength lightweight concrete. An increase in the cementitious content from 420 to 450 kg/m3 does not significantly increase the strength of lightweight aggregate concrete. The relationship between the flexural and compressive strength at 28 days can be represented by the equation fr=0.69/fck. The elastic modulus was found to be much lower than that of normal weight concrete, ranging from 15.0 to 20.3 GPa. The addition of PFA increases the slump and density of lightweight aggregate concrete.

Carbon↗

PubMed2002

NDT response of spectral analysis of surface wave method to multi-layer thin high-strength concrete structures.

This study presents the results of the non-destructive testing using spectral analysis of surface waves (SASW) based on high-strength concrete materials. This SASW method was used to evaluate the compressive strength of single-layer high-strength concrete slabs through a correlation with the surface wave velocities. This paper also presents the relationship between the theoretical and experimental compact dispersion curves when the SASW test is applied to multi-layer thin high-strength concrete slab systems with a finite thickness. The test results show that the surface wave velocity profile obtained from the theoretical dispersion curve has lower values than the profile obtained from the experimental compact dispersion curve under the condition of a finite thickness due to different boundary conditions and reflections from the boundaries. Based on the measured response, an experimental study was conducted to examine if the dispersive characteristics of Rayleigh wave exist in the multi-layer high-strength concrete slab systems. This study can be utilized in examining structural elements of high-strength concrete structures and can also be applied in the integrity analysis of high-strength concrete structures with a finite thickness.

Journal Article↗

PubMed1996

Combined models of ultrasound velocity and attenuation for predicting trabecular bone strength and mineral density.

Three quantitative ultrasound parameters and their combinations were examined as possible predictors of the bone mineral density and compressive strength of human cancellous bone. Seventy-three trabecular bone cubes obtained from female cadaveric tibiae were measured by quantitative computed tomography. Measurements of the ultrasound velocity, ultrasound attenuation at 0.5 MHz and broad-band ultrasound attenuation were made in three orthogonal anatomical directions. The specimens were then tested to failure in compression, 38 in the anterior/posterior direction and 35 in the superior/inferior direction. The apparent density of all specimens was also found. Linear regressions showed that bone mineral density and strength were significantly correlated with each ultrasonic parameter in each direction (P < 0.05). Linear combinatinations of two ultrasound parameters were significantly better predictors than single parameters, although the optimum pair of parameters differed with direction. Three parameter models did not further improve predictability.

Journal Article↗

PubMed1980

[Studies on the dynamic durability of dental restorative materials. (Part 2) Properties for the repeated impact compressive load ot composite resins (author's transl)].

Based on the fracture energy form the compression test of composite resins under the repeated impact loads in compression after stored for a period in water at 37 degrees C, the dynamic durability of commercially used composite resins was evaluated. The results obtained were summarized as follows. (1) The fracture energy of composite resins under the repeated impact compressive loads after stored in water at 37 degrees C is clearly lower than the initial fracture energy. Particularly the decrement of the initial fracture energy for Concise, Epolite 100 and Superlux after stored for 30 days in water at 37 degrees C is influenced considerably both by the physicochemical degradation caused by water and the mechanical deterioration caused by the repeated impact compressive loads, but Clearfil is superior to the mechanical deterioration. (2) In each composite resins, there is a close correlation between fracture energy and compressive strain. In composite resins without Superlux, also a correlation is in fracture energy and compressive strength. (3) In clearfil, concise and Epolite 100, the morphology of fracture in compression test of composite resins which are subjected to and are subjected to the repeated impact loads in compression is classified in a mode of shear fracture, but in Superlux, a mode of crack fracture.

Composite Resins↗

PubMed2004

Novel bioactive and biodegradable glass ceramics with high mechanical strength in the CaO--SiO2--B2O3 system.

Novel bioactive and biodegradable glass ceramics with high mechanical strength in the (50-x/2)CaO. SiO(2)--xB(2)O(3) (4.2 < or = x < or = 17.2) system were investigated. The systems consisted of three phases: monoclinic wollastonite, calcium metaborate, and amorphous borosilicate matrix. The glass ceramics containing 4.2 mol% and 8.4 mol% B(2)O(3) showed high bulk density and a dense microstructure. Mechanical strengths of the glass ceramics were higher than those of other bioactive ceramics: high compressive strength (2813 MPa), bending strength of 212 MPa, and fracture toughness of 3.12 MPa. m(1/2). The glass-ceramic formed apatite layer on their surface in the simulated body fluid and showed significant biodegradation. The degree of apatite formation in the glass ceramics depended on the calcium metaborate content and borosilicate glassy matrix. Additional calcium metaborate and borosilicate glassy matrix increased the apatite formation rate on the surface. It might be likely that calcium metaborate causes supersaturation of Ca ions, for its high solubility in SBF and the water-reactive borosilicate glassy matrix formed Sibond;OH groups on the surface to provide nucleation sites for apatite formation. Also, through in vitro test for the biocompatibility of the CaO--SiO(2)--B(2)O(3) glass ceramics, no cytotoxicity of the glass ceramics were found. The results on bioactivity and noncytotoxicity indicated that glass ceramics in the (50-x/2)CaO. SiO(2)--xB(2)O(3) (4.2 < or = x < or = 17.2) system could be useful as a biodegradable bone replacement material.

Biocompatible Materials↗

PubMed2004

Protein-loaded bioresorbable fibers and expandable stents: Mechanical properties and protein release.

There is an increasing interest in bioresorbable polymeric stents for coronary, urethral and tracheal applications. These stents can support body conduits during their healing process and release biologically active agents from an internal reservoir to the surrounding tissue. A removal operation is not needed. Bioresorbable poly(L-lactic acid) fibers were prepared through melt spinning accompanied by a postpreparation drawing process. Novel expandable bioresorbable stents were developed from these fibers. Bioresorbable microspheres containing albumin were prepared and attached to the stents, to serve as a protein reservoir coating. The controlled release of albumin from the microsphere-loaded stent was studied. The fibers combine high strength and modulus, together with good ductility and flexibility. An increase in draw ratio increases the tensile strength and modulus and decreases the ultimate strain. The stents demonstrated excellent initial radial compression strength and good in vitro degradation resistivity, which makes them applicable for supporting blood vessels for at least 20 weeks. Microspheres bound to these stents enable effective protein loading, without reducing the stent's mechanical properties. The protein release from the microsphere-loaded stent occurs by diffusion, is determined mainly by the initial molecular weight of the bioresorbable polymer and its erosion rate, and is strongly affected by the microsphere structure.

Animals↗

PubMed1995

A comparison of three methods for preparing reversible hydrocolloid duplicating material.

This study compared the effects of repeated microwave oven and double-boiler liquefactions and prolonged autoduplicator storage on four physical properties of one reversible hydrocolloid duplicating material. No significant differences were observed between the linear dimensional change and detail reproduction of the three liquefaction techniques. Tear strength differences most clearly distinguished the techniques and effects of aging. Fifteen double-boiler remeltings produced tear strength values lower than those recorded for material stored in an autoduplicator for 2 weeks. Thirty microwave melting cycles still produced tear strength values equivalent to that of the autoduplicator material. After 30 melting cycles the compressive strengths of the microwave and double-boiler materials were inferior to that of the stored autoduplicator material.

Alginates↗

PubMed1996

Strength of porcelain fused to titanium beams.

The purposes of this study were to measure strengths of layered porcelain fused to titanium beams, determine failure modes, and investigate the porcelain-titanium interface. A three-point flexural test and formulas derived especially for this purpose were used. The strength of layered porcelain-ceramic beams was limited by the cohesive tensile or compressive strengths of the porcelain, not by the porcelain-titanium interfacial bond, namely, the porcelain failure occurred at lower loads than did failure of the porcelain-titanium interface. The porcelain-titanium bond strength was at least 26 MPa. Scanning electron microscopy and energy-dispersive x-ray spectroscopy demonstrated that the bond was limited by delamination of a thin titanium-titanium oxide interface. Theoretic curves that describe effects of relative layer and total thickness on the force-bearing capacity of model beams were plotted. These curves indicated that porcelain-titanium prostheses should be made as thick as is practical, but the relative thickness of the porcelain and titanium layers would be less important.

Analysis of Variance↗

PubMed1991

[Comparative material studies on dental stones in accordance with DIN 13911].

It was the object of this investigation to compare nine high-strength stone plasters in terms of visual appearance, pouring time, setting time, setting expansion, compressive strength and detail reproduction in accordance with DIN 13911 and ISO 6873 using both standard consistency as indicated in the industrial standard and the water-to-powder ratio as indicated by the manufacturer. None of the tested stones met the visual requirements in all points. Regarding their physical properties, six tested stones were up to standard. Three stones failed to meet the DIN and ISO requirements. Following the manufacturer's mixing instructions resulted in a significant improvement in material properties as against standard consistency. Disregarding some minor improvements required, DIN 13911 and ISO 6873 are useful standards for a standardized comparison of dental plasters.

Calcium Sulfate↗

PubMed1997

The effects of density and test conditions on measured compression and shear strength of cancellous bone from the lumbar vertebrae of ewes.

An animal model (the ewe) was used to study mechanical parameters of cancellous bone specimens. Compression and shear tests were conducted on ewe vertebral trabecular bone (L1-L5) from old ewes (mean age: 9 years) under two different conditions: first, at room temperature in air ("standard" test conditions); and secondly, in a physiological saline bath regulated at 37 degrees C. The parameters obtained under "standard" test conditions with a uniaxial compression test were the mean value of the maximum strength (sigma max = 22.3 (7.06) MPa), Young's modulus (E = 1510 (784) MPa), the strain at maximum strength (epsilon sigma max = 3.21 (0.8) percent) and the energy absorbed during the test (W = 0.3 (0.12) MJ.m-3). No significant change was found when the test was carried out in a saline bath at 37 degrees C (p < 0.0005). An original shear test was performed to evaluate the shear strength which was found to vary from 7.5 (4.7) to 14.6 (8.53) MPa under "standard" test conditions depending on the method of calculation. Testing of the specimens in a 37 degrees C physiological saline bath induced a decrease in the shear strength from 32.5 percent (p < 0.0005) to 37.3 percent (p < 0.0001) of those measured under "standard" test conditions. The non-destructive measurement of the Bone Mineral Density (BMD) accounted for up to 73.3 percent of the maximum compressive strength sigma max and 61.5 percent of the maximum shear strength tau max determined in saline solution at 37 degrees C. These results showed that other parameters influencing the mechanical properties of trabecular bone and its structure appeared to be essential.

Absorptiometry, Photon↗

PubMed1990

In vitro biomechanical study of female geriatric cervical vertebral bodies.

Compressive strength tests were conducted on fresh human geriatric female cervical vertebral bodies. Nineteen specimens were compressed to 50% of their initial height using an electrohydraulic testing device. The mechanical force-deflection response was sigmoidal with continuously changing resistance. The mean cross-sectional area and bone mineral content (BMC) of the vertebral bodies progressively increased from C3 (area: 333.8 mm2, BMC: 1.56 g) to C6 (area: 499.7 mm2, BMC: 2.18 g). The maximum compressive force increased from 1060 N at C3 to 1787 N at C6. The stiffness and the energy absorbed at failure also increased from C3 to C6 (stiffness: 279.95 to 556.41 N mm-1, energy: 2.45 to 4.16 J). These parameters demonstrated a decreasing tendency from C6 to C7. The relatively higher biomechanical parameters at the sixth vertebral level compared with its caudad and cephalad counterparts may be due to the fact the transition of the cervical lordosis to thoracic kyphosis begins at this level. Furthermore, the change in the anatomy of the unicinate processes in the cervical column around this region may also be a contributing factor.

Aged↗

PubMedDate not supplied

The effect of venting on the strength of Dicor and Hi-Ceram ceramic crowns.

Research has shown that external venting improves the marginal fit of cast crowns by decreasing hydrostatic pressure during seating. In turn, improving marginal fit has been shown to increase the strength of castable glass and other porcelain systems. This study evaluated the effect on the compressive strength of crowns with vent holes placed during and after fabrication. Forty-five artificial crowns were made from each material and divided into three equal groups: (1) crowns without vent holes, (2) crowns with a vent hole placed before casting, and (3) crowns with a vent hole placed using a rotary diamond instrument after casting. Standardized crowns were acid etched, silane treated, and filled with epoxy resin to provide a support base for testing. The crowns were then loaded to failure. One-way analysis of variance showed a significant difference among groups. Scheffe's Multiple Comparison Test was used for discrimination. The Dicor unaltered and fabricated vent group and the Hi-Ceram unaltered group had significantly higher resistance to fracture.

Aluminum Oxide↗

PubMedDate not supplied

Properties related to strength and resistance to abrasion of VariGlass VLC, Fuji II L.C., Ketac-Silver, and Z-100 composite resin.

The purpose of this study was to evaluate the properties related to the strength and resistance to abrasion of new Type II lightcured glass ionomers, VariGlass VLC, and Fuji L.C., and to compare the results with Ketac-Silver and Z-100 composite resin. Each material was tested for strength with an Instron Universal Testing Machine and for resistance to abrasion with a motor-driven machine. The strengths of Z-100 were the highest. Among glass ionomers, Ketac-Silver had higher compressive strength, but lower diametral tensile and transverse strengths than the others; and Fuji II L.C. had higher strengths than VariGlass VLC. VariGlass VLC showed the greatest resistance to abrasion, followed respectively by Z-100, Fuji II L.C. and Ketac-Silver. ANOVA indicated significant differences in strengths and abrasion resistance, except, the volume losses of Fuji II L.C. and Ketac-Silver in the toothbrushing test were not significantly different (p < 0.01). The results support VariGlass VLC and Fuji II L.C. as alternative filling materials in Class III and V situations, but they are not recommended for stress-bearing restorations.

Acrylic Resins↗

PubMed2006

Sludge ash/hydrated lime on the geotechnical properties of soft soil.

In this study, an effort to improve the properties and strength of soil, sewage sludge ash (SSA) and hydrated lime are applied to stabilize soft cohesive subgrade soil. Five different ratios (in weight percentage), 0%, 2%, 4%, 8%, and 16%, of sludge ash/hydrated lime are proposed for mixture with cohesive soil. Then, the effects of the different proportions of SSA/hydrated lime on soft cohesive soil are studied. Test results indicate that the unconfined compressive strength of specimens with additives was raised from three to seven times better than that of the untreated soil, and swelling behaviors were also effectively reduced for those specimens. Results of triaxial compression test indicate that the shear strength parameter, c, rose with an increased amount of additives and improved from 30 to 50-70kPa. On the whole, SSA/hydrated lime could particularly improve the geotechnical properties of cohesive subgrade soil.

Calcium Compounds↗

PubMed2003

Physico-mechanical properties of a fast-set highly viscous GIC restorative.

UNLABELLED: The fast-setting reaction of 'fast-set' highly viscous glass-ionomer cements (GIC) may result in superior mechanical properties and good wear resistance as the material can theoretically achieve sufficient strength to resist masticatory loads within a shorter time. The aim of this study was to determine the hardness, strength (compressive and diametral tensile) and wear resistance of a 'fast-set' highly viscous GIC (Fuji IX GP Fast). Its regular set counterpart (Fuji IX GP) was used for comparison. The glass powders of the two cements were also characterized. Hardness testing [Vickers' hardness number (VHN)] was performed with a digital hardness tester (load=50 g; dwell time=30 s) and compressive/diametral tensile strength testing (MPa) was conducted based upon British Standards specification for GICs (BS6039, 1981). Wear testing was conducted using a reciprocal compression-sliding wear instrumentation at 20 MPa contact stress against SS304 counter-bodies with distilled water as lubricant. All specimens were immersed in distilled water at 37 degrees C and tested 24 h after start of mixing. Further mechanical tests (hardness and strength) were conducted with specimens stored for 1 week in distilled water at 37 degrees C. The glass powders were characterized using laser particle sizing, standard electron microscope (SEM) and energy dispressure X-ray (EDX) analysis. Results were analysed using multiple analysis of variance (manova) and independent samples t-test at significance level 0.05. No significant difference in hardness, compressive and diametral tensile strength was observed between Fuji IX GP and Fuji IX GP Fast at 1 day. There was also no significant difference in wear at all cyclic intervals. Although the difference in strength was not significant between the two cements at 1 week, Fuji IX GP Fast was significantly harder than Fuji IX GP. Particle size of both cements ranged from 0.3 to 200 microm. The mean particle sizes were, however, different and were 13.43 and 7.13 microm for Fuji IX GP and Fuji IX GP Fast, respectively. Fuji IX GP Fast offers no other advantage over Fuji IX GP with the exception of improved hardness. CLINICAL RELEVANCE: Besides being harder, the fast-set highly viscous GIC restorative offers no other physico-mechanical advantage over its regular set counterpart.

Dental Restoration Wear↗

PubMed1991

Strength of phosphate-bonded investments at high temperature.

There has been little reported on the strength of phosphate-bonded investments, and in particular the role of 'special liquids' in this context is poorly understood. Using a novel test design, sequential testing of an investment diaphragm using a variable casting metal mass, a measure of the effect of 'special liquid' on strength under actual casting conditions has been obtained. The use of special liquid was found to increase substantially the strength of the four products tested. This test may provide more useful data than the conventional compressive strength test, which may give misleading information, especially if performed at room temperature.

Dental Bonding↗