Crack Distribution Patterns Research Articles

Experimental and variational-based analytical investigation of multiple cracked angle-ply laminates

A unit cell based method is developed based on variational principles to derive the stress state and effective mechanical properties of angle-ply laminates of type [θm(o)/θn(i)]s containing whether mid-ply or outer-ply matrix cracks positioning in a symmetric or staggered pattern through the laminate. All plausible matrix crack distribution patterns are considered and implementing the principle of minimum complementary energy, an admissible stress field is derived. For the first time effects of ply refinement technique, layup configuration and crack distribution pattern on the stress state and degradation of mechanical properties of angle-ply laminates are investigated and compared to finite element results. CFRP test specimens are prepared and optical microscopy is utilized to detect matrix crack densities during tensile tests. Obtained analytical stiffness reductions for different crack densities are confirmed to be in agreement with experimental observations.

Experimental observation and energy based analytical investigation of matrix cracking distribution pattern in angle-ply laminates

An energy based criteria is developed to predict the leading distribution pattern of matrix cracks in the damage mode competition in angle-ply laminates of type θm1/θn2s subject to uniaxial tensile loading. For the first time in the literature, all plausible matrix crack distribution patterns, namely mid-ply or staggered/symmetric outer-ply cracking are considered and energy release rate for initiation of each case is derived. Different geometrical effects such as ply orientation, thickness ratios and scale effects are investigated on the initiation distribution pattern of matrix cracks. The results show that distribution pattern of matrix cracks is directly affected by geometrical factors. Test specimens with different geometrical characteristics are prepared from unidirectional carbon-epoxy and an experimental test setup is prepared to capture the distribution pattern of matrix cracks during tensile loading. The predicted matrix crack distribution patterns of all specimens are verified by experimental observations.

Anti-blast properties of RC superimposed slab shear wall

In order to analyze the anti-blast properties of the RC superimposed slab's shear wall, comparative experimental studies of two RC superimposed slab shear walls and two in-situ cast shear walls under explosion were conducted. The structural failure feature, deformation capability, bearing capacity and crack distribution pattern were analyzed systematically. The result shows that the failure mode of the RC superimposed slab shear wall is similar to that of the in-situ cast shear wall. The stiffness of two kinds of specimen are basically identical within the elastic stage. But the post-cracking stiffness' descending speed of the in-situ cast shear wall is greater than that of the RC superimposed slab shear wall. The RC superimposed slab effectively restrained the crack extension and there were no shear failure throughout the loading procedure, which proves its high integrity. The blasting-resistance performance of the RC superimposed slab shear wall is superior to that of the in-situ cast shear wall.

Modified Fatigue Model for Hourglass-Shaped Steel Strip Damper Subjected to Cyclic Loadings

AbstractMetallic dampers have been used to dissipate large amounts of seismic energy through inelastic deformation in order to minimize damages to the main structural components. However, cumulative inelastic deformation of the metallic dampers results in fatigue cracks, so the life of the device may be reduced significantly. In this paper, an experimental study was carried out to investigate the low-cycle fatigue damage for the proposed hourglass-shaped strip damper (HSD). Four different types of cyclic loadings were applied in this test. The microstructures of the fracture surfaces and the crack distribution patterns were also observed. From the results, it was found that the shape of HSD was well designed for excellent fatigue performance, and the low-cycle fatigue characteristics of the steel strip damper could be well defined by the Manson-Coffin relationship. To consider the mean deformation and the loading sequences, a modified fatigue damage prediction model was proposed that incorporates the effe...

Direct Measurement of Inter-Filament Resistance in Superconducting Multifilamentary NbTi and ${\rm Nb}_{3}{\rm Sn}$ Strands

A quantitative knowledge of inter-filament transverse resistance will allow us to describe current redistribution processes inside strands more accurately. This is particularly important for the analysis of the influence of strain and crack distribution patterns in Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn filaments on the shape of the voltage-current curves. Several indirect methods are commonly used to assess inter-filament resistance. Here we use a direct method to measure transverse inter-filament resistance and filament-to-matrix contact resistance. Two four-probe voltage-current methods are developed for measurements below 10 K at various background magnetic fields. In addition to FEM (Finite Element Method) simulation, also a new 3D strand model is developed to simulate the current- and voltage distributions. The experimental methods, first results as well as the simulations using the FEM method and new 3D strand model are described.

Limpet grazing on a physically stressful Patagonian rocky shore

Many theories of consumer control of communities have come from studies conducted in relatively benign, temperate zone rocky intertidal systems. Here, we examine gastropod grazing and the maintenance of bare space on a dry, wind-swept rocky shore of Patagonia, Argentina. Two limpet species are the primary intertidal grazers. Siphonaria lessoni dominates mid and high intertidal zones, while Nacella magellanica dominates the lower zone. In all zones, limpet densities are positively correlated with bare space and the occurrence of cracks. Tethering experiments revealed that: (1) physical stress sets the upper distribution limit of both limpets, (2) predators, such as oyster catchers, regulate Nacella populations and may restrict them to cracks and vertical surfaces, and (3) desiccation stress appears to drive similar crack distribution patterns of Siphonaria in the upper intertidal. Experimental removal of limpets in each intertidal zone indicated that limpets have: (1) no detectable effect in the high intertidal where physical forces dominate community organization, (2) weak impacts at mid-elevations as grazing only limited the abundance of fleshy algae with physical forces again dominating community structure, and (3) relatively stronger, but still weak impacts in the low zone. These results suggest that grazing impacts on Argentine rocky shores are weak in comparison to the physical stresses (e.g. high winds, low humidity) that largely determine structure in this system. The dominance of physical forcing in this system occurs despite having similar grazer densities to other temperate, but comparatively wet, rocky shorelines (e.g. British Isles) where top-down control is strong.

Methodology for Estimating Remaining Life of Continuously Reinforced Concrete Pavements

A methodology was developed for estimating the remaining life of a nonoverlaid continuously reinforced concrete pavement. The models presented use several key predictors: the early-age crack distribution pattern in the concrete caused by volumetric changes, the coarse aggregate type used, and the presence or absence of a swelling subgrade that will accelerate the rate of development in later life due to dynamic loadings. Considering these factors, the models can accurately estimate the additional 18-kip equivalent single axle loads (ESALs) that will take the pavement from its current condition in terms of failures per mile (FPM) to a user-defined failure threshold, such as 10 or 15 FPM. Using traffic models developed in another study, the number of additional ESALs to can be translated into time to for planning purposes. The overall objective of the analysis is to determine the optimum time to overlay—before and preferably before the onset of irreparable damage to the pav...

Methodology for Estimating Remaining Life of Continuously Reinforced Concrete Pavements

A methodology was developed for estimating the remaining life of a nonoverlaid continuously reinforced concrete pavement. The models presented use several key predictors: the early-age crack distribution pattern in the concrete caused by volumetric changes, the coarse aggregate type used, and the presence or absence of a swelling subgrade that will accelerate the rate of failure development in later life due to dynamic loadings. Considering these factors, the models can accurately estimate the additional 18-kip equivalent single axle loads (ESALs) that will take the pavement from its current condition in terms of failures per mile (FPM) to a user-defined “failure threshold,” such as 10 or 15 FPM. Using traffic models developed in another study, the number of additional ESALs to failure can be translated into time to failure for planning purposes. The overall objective of the analysis is to determine the optimum time to overlay—before failure and preferably before the onset of irreparable damage to the pavement.

Crack geometries and deformation by the crack-seal mechanism in the Sambagawa metamorphic belt

Geometries of cracks sealed by quartz formed in the retrograde metamorphism of the Sambagawa high-pressure type metamorphic belt were measured. The relation obtained between width and length of cracks displays a power law having power exponents ranging from 0.64 to 0.98 for a wide range of lengths. The crack aspect ratios increase from 0.008 in the chlorite zone to 0.03 in the biotite zone. The average grain size of infilling quartz is proportional to the crack width, suggesting that the crack width is governed by the growth rate of infilling quartz. The frequency distribution of spacings of neighbouring cracks shows a power-law relation. Combining these data, deformation by the crack-seal mechanism is inferred to be controlled by the crack-spacing power index (fractal dimension) and growth rate of infilling quartz. The boundary between deformation by the crack-seal mechanism and the dislocation-creep regime is delineated as a function of differential stress, temperature and fractal dimension of the crack distribution pattern.