Flexural strength

About: Flexural strength is a research topic. Over the lifetime, 52123 publications have been published within this topic receiving 846504 citations. The topic is also known as: bending strength & modulus of rupture.

Measurement of the Bending Strength of Vapor-Liquid-Solid Grown Silicon Nanowires

Abstract: The fracture strength of silicon nanowires grown on a [111] silicon substrate by the vapor-liquid-solid process was measured. The nanowires, with diameters between 100 and 200 nm and a typical length of 2 Im, were subjected to bending tests using an atomic force microscopy setup inside a scanning electron microscope. The average strength calculated from the maximum nanowire deflection before fracture was around 12 GPa, which is 6% of the Young’s modulus of silicon along the nanowire direction. This value is close to the theoretical fracture strength, which indicates that surface or volume defects, if present, play only a minor role in fracture initiation. Nanowires (NWs) are of interdisciplinary interest to applications in the fields of biomedical sensing, nano- and optoelectronics and photovoltaics due to their electrical, optical, mechanical, and geometrical properties that may deviate substantially from bulk. 1 To name some particularly exciting applications, the reader is referred to the following list: (i) high-frequency electromechanical resonators, 2 (ii) high-aspect ratio tips for surface probe microscopy, 3 (iii) sensor array for electrical detection of cancer markers, 4 (iv) Si NW arrays for photovoltaics, 5 and (v) nanoscale light-emitting diodes. 6 For all these applications the mechanical stability of the NWs is essential for their atomic scale manipulation, functionalization, or integration into device schemes. Several methods were used in the past to access the mechanical properties of silicon NWs and nanobeams. An atomic force microscope (AFM) was used for bending tests of single crystal, micromachined silicon beams (from 1 mm down to 200 nm in width, beam axis oriented in [110] direction). No change in Young’s modulus, but an increase in bending strength by a factor of up to 38 was observed from the millimeter down to the nanometer scale. 7 AFM measurements were also done on silicon NWs (from 10 to 100 nm in diameter, grown along the [111] direction) where a bending modulus of 186 GPa (188 GPa in bulk) was measured. 8

Effectiveness of stirrups and steel fibres as shear reinforcement

Abstract: This paper presents the results of experimental tests carried out on rectangular simply supported beams made of hooked steel fibre reinforced concrete with and without stirrups, subjected to two-point symmetrically placed vertical loads. The tests, carried out with controlled displacements, allow one to record complete load–deflection curves by means of which it is possible to deduce information on dissipative capacity and ductile behaviour up to failure. Depending on the amount of transverse reinforcement, volume fraction of fibres added in the mix and shear span, the collapse mechanism is due to predominant shear or flexure, thus showing the influence of the aforementioned structural parameters on the load carrying capacity and the post-peak behaviour of the beam. In particular, the results show that the inclusion of fibres in adequate percentage can change the brittle mode of failure characterizing shear collapse into a ductile flexural mechanism, confirming the possibility of achieving analogous performance by using reinforcing fibres instead of increasing the amount of transverse reinforcement. The ultimate values of the shear stresses recorded experimentally are compared with the corresponding values deduced by semiempirical expressions available in the literature and the correlation is satisfactory.

Porosity dependence and mechanism of brittle fracture in sandstones

Abstract: Brittle fracture tests of 105 fine-grained quartz arenites were conducted at 25°C, 1.0-kb confining pressure, a constant strain rate of 6.5 × 10−5/sec, and pore pressure ranging from 0 to 750 bars. Orientation of planar anisotropy (bedding or cross-bedding) with respect to principal stresses has little influence on the fracture strength. The Donath orientation effect depends on rock type. Strong dependence of fracture strength on porosity is of the form y = axb (where y equals stress difference at failure, x equals porosity, and a > 0 > b; in our samples, values for a ranged between 16 and 25 kb, and b between −0.8 and −1.0). Through-going shear fractures result from coalescence of grain boundary cracks, extension fractures within grains, and void space. Rocks with low porosity develop through-going shears only after many grains are extension fractured. The functional relationship between porosity and fracture strength derives from the lower energy required for propagating cracks to use void space rather than forming extension fractures.