Uniaxial Strength Data Research Articles

Non‐proportional size scaling of strength of concrete in uniaxial and biaxial loading conditions

AbstractA procedure for non‐proportional size scaling of the strength of concrete based on the weakest‐link statistics is proposed to synchronize strength data from specimens of different geometries and different loading modes. The procedure relies on proportional size scaling of strength to determine the parameters of the statistical model and often on finite element analysis to calculate the coefficient of the equivalent strength. The approach for non‐proportional size scaling is capable to synchronize the uniaxial strength data of concrete from uniaxial tensile specimens and 3‐point bending specimens, or the biaxial tensile strength data of circular plates in different loading mode. The non‐transference of the uniaxial strength data to the biaxial strength data is unclear in its mechanism but possibly due to the variation of statistical distribution of microcracks with stress states in different specimens.

Experimental study of size effect on quasi-static strengths for short glass fibre-reinforced plastics

The present paper examines size effect on the strength of short glass fibre-reinforced phenolic resin (SGP) composites made by press moulding with different loading modes and specimen shapes. Three- and four-point flexural tests and tension–torsion combined tests were conducted at room temperature in order to evaluate the influence of Vf and loading mode on fracture strength. The obtained uniaxial strength data were analysed using the Weibull statistical theory. The relationship between fracture strength and effective volume was investigated based on the Weibull statistical theory and agreed well with the effective volume theory (EVT), regardless of specimen size, dimensions or loading mode. The experimental results revealed that the tension–torsion multiaxial SGP strength was in agreement with the Tsai–Hill failure criterion. The EVT was also applied to the Tsai–Hill failure criterion to consider the size effect, and the validity of the proposed method was confirmed experimentally.

Geopolymerization reaction to consolidate incoherent pozzolanic soil

Pozzolanic material-based geopolymer has been proposed as a solving methodology to the geohazards, due to pozzolanic collapsible soils widely present in the South Italy. The geopolymer was synthesized from pozzolana material under activation of NaOH 10 M or slurry of NaAlO2 in NaOH 10 M solution. The specimens were cured at 25 °C and 100% RH for different ageing times. The effect of the two activation methods on the properties of the geopolymer was investigated by means of X-ray diffraction, scanning electron microscopy (SEM), FTIR spectroscopy, nuclear magnetic resonance (27Al and 29Si NMR) and uniaxial compression tests. XRD, NMR and IR analysis indicate the geopolymer is generated by the dissolution of the silico-aluminate phases present in the pozzolana and the successive re-organization in amorphous and crystalline neo-formed phases. The spectroscopic evidences confirm that the 4-coordinated Al atoms present in the neat pozzolana and in the NaAlO2 change their coordination state splitting between 6- and 4-coordinated atoms, modifying the traditional chemistry of polysialate formation. SEM results show the synthesized geo-polymer maintained the granular morphology of the pozzolana and the geo-polymeric reactions occurred mainly at the surface of pozzolana particulates. Furthermore, uniaxial strength data increase gradually upon the curing time, until 40 MPa for the specimens activated with the slurry system.

Microstructural and Geometrical Factors Influencing the Mechanical Failure of Polysilicon for MEMS

AbstractThe failure strength of polycrystalline silicon is discussed in terms of activation of critical flaws, as well as the material microstructure and inhomogeneity. The Weibull probability density function parameters were obtained to deduce the scaling of material and component strength and to identify critical flaw populations, especially when two or more flaw sets are concurrently active. It was shown that scaling of strength changes for small feature sizes, which limits the applicability of strength data from large MEMS components to self-similar small MEMS components. On the other hand, the probability of failure of small components is described by a larger Weibull material stress parameter, which makes uniaxial strength data a conservative design approach. Furthermore, according to mode I and mixed mode I/II fracture studies for polysilicon, it is concluded that microstructural inhomogeneity alone accounts for 50% scatter in strength (with reference to the minimum recorded value). Thus, the conditions for applicability of the Weibull probability density function are rather weak in polycrystalline silicon, because flaws of the same length that are subjected to the same macroscopic stresses are not always critical.

Development of a Bending-Test Device for Small Samples

Flexural testing of rectangular beams in 4-point geometry is a simple and widely used standardised method [1] to gain uniaxial strength data of ceramic materials. To evaluate the strength of components samples have to be cut out of them, which is not always possible in the prescribed standardised size. Therefore the miniaturisation of the 4-point bending-test is analysed. The errors in determined flexural strength arising from geometry and measuring inaccuracies are calculated and expressed depending on the outer span length. The possibilities of adequate specimen preparation are investigated. The limitation of the resulting relative error in flexural strength to 10% determines minimal dimensions of samples and fixtures. The applicability of such a device is tested by comparing two sets of strength values measured on small and DIN-fixtures with the help of Weibull statistics.

Fracture Strength Evaluation of Sintered Silicon Nitride Disks with Shoulder Fillet at Room Temperature and at 1000.DEG.C..

Bending fracture tests of sintered silicon nitride disks with shoulder fillet were performed at room temperature and at l000°C. The comparison of the experimental results with statistical reliability analysis showed that strength evaluation method based on the 2-parameter Weibull theory can be applied to estimate the strength of multiaxial stress stated ceramic components. It was observed that the choice of fracture criteria had little effect to the reliability analysis. The correlation of the strength of ceramic components under multiaxial stress state with uniaxial Strength data was made possible using the concept of equivalent stess and effective volume.

The estimation of the experimental and basic components of the observed variance of rock strength

The Estimation of the Experimental and Basic Components of the Observed Variance of Rock Strength The intercept of the strength correlelogram over distance is used to estimate the proportions of the observed strength variance which can be attributed to the testing (experimental) procedure and to the basic differences between the strengths of the specimens. The method is applied to sandstone uniaxial strength data (Wiid, 1968) where approximately half of the observed variance is experimental and half basic. A spatial trend accounts for most of the basic variance. The uniaxial strength is also spatially correlated with the triaxial strength. It is shown that the results of testing procedures of equal reliability will be poorly correlated if the experimental components of variance are large.