Showing papers on "Direct shear test published in 2018"

Interfacial bonding strength of short carbon fiber/acrylonitrile-butadiene-styrene composites fabricated by fused deposition modeling

Abstract: This work aims to characterize the interfacial bonding strength between printed wires of acrylonitrile-butadiene-styrene (ABS), carbon nanotube reinforced ABS (CNTABS) and short carbon fiber reinforced ABS (CFABS) specimens fabricated by fused deposition modeling. The in-plane tensile shear test and double notch shear test methods using ±45° specimens were used. The in-plane tensile shear strength of CFABS specimen is close to that of CNTABS specimen, and both of them are greater than that of ABS specimen. Double notch shear strengths are smaller than in-plane tensile shear strength of CFABS specimens at all three printing speeds studied. Also, the shear strengths of CFABS specimens decrease with increasing printing speed and layer thickness. X-ray micro-computed tomography examination concluded that CFABS specimens have the largest porosity compared with ABS and CNTABS specimens at corresponding raster orientation, especially for ±45° specimens. Matrix fracture and fiber pull-out, as well as fiber-matrix interfacial debonding are the dominating failure modes of CFABS specimen.

Effect of Particle Size and Cohesion on Powder Yielding and Flow

Abstract: The bulk properties of powders depend on material characteristics and size of the primary particles. During storage and transportation processes in the powder processing industry, the material undergoes various modes of deformation and stress conditions, e.g., due to compression or shear. In many applications, it is important to know when powders are yielding, i.e. when they start to flow under shear; in other cases it is necessary to know how much stress is needed to keep them flowing. The measurement of powder yield and flow properties is still a challenge and will be addressed in this study. In the framework of the collaborative project T-MAPPP, a large set of shear experiments using different shear devices, namely the Jenike shear tester, the ELE direct shear tester, the Schulze ring shear tester and the FT4 powder rheometer, have been carried out on eight chemically-identical limestone powders of different particle sizes in a wide range of confining stresses. These experiments serve two goals: i) to test the reproducibility/consistency among different shear devices and testing protocols; ii) to relate the bulk behaviour to microscopic particle properties, focusing on the effect of particle size and thus inter-particle cohesion. The experiments show high repeatability for all shear devices, though some of them show more fluctuations than others. All devices provide consistent results, where the FT4 powder rheometer gives lower yield/steady state stress values, due to a different pre-shearing protocol. As expected, the bulk cohesion decreases with increasing particle size (up to 150 μm), due to the decrease of inter-particle cohesion. The bulk friction, characterized in different ways, is following a similar decreasing trend, whereas the bulk density increases with particle size in this range. Interestingly, for samples with particle sizes larger than 150 μm, the bulk cohesion increases slightly, while the bulk friction increases considerably—presumably due to particle interlocking effects—up to magnitudes comparable to those of the finest powders. Furthermore, removing the fines from the coarse powder samples reduces the bulk cohesion and bulk density, but has a negligible effect on the bulk friction. In addition to providing useful insights into the role of microscopically attractive, van der Waals, gravitational and/or compressive forces for the macroscopic bulk powder flow behaviour, the experimental data provide a robust database of cohesive and frictional fine powders for industrially relevant designs such as silos, as well as for calibration and validation of models and computer simulations.

Shear Strength and Cracking Process of Non-persistent Jointed Rocks: An Extensive Experimental Investigation

Abstract: In this paper, a number of artificial rock specimens with two parallel (stepped and coplanar) non-persistent joints were subjected to direct shearing. The effects of bridge length (L), bridge angle (γ), joint roughness coefficient (JRC) and normal stress (σ n) on shear strength and cracking process of non-persistent jointed rock were studied extensively. The experimental program was designed based on Taguchi method, and the validity of the resulting data was assessed using analysis of variance. The results revealed that σ n and γ have the maximum and minimum effects on shear strength, respectively. Also, increase in L from 10 to 60 mm led to decrease in shear strength where high level of JRC profile and σ n led to the initiation of tensile cracks due to asperity interlocking. Such tensile cracks are known as “interlocking cracks” which normally initiate from the asperity and then propagate toward the specimen boundaries. Finally, the cracking process of specimens was classified into three categories, namely tensile cracking, shear cracking and combination of tension and shear or mixed mode tensile–shear cracking.

Shear Behaviour and Acoustic Emission Characteristics of Bolted Rock Joints with Different Roughnesses

Abstract: To study shear failure, acoustic emission counts and characteristics of bolted jointed rock-like specimens are evaluated under compressive shear loading. Model joint surfaces with different roughnesses are made of rock-like material (i.e. cement). The jointed rock masses are anchored with bolts with different elongation rates. The characteristics of the shear mechanical properties, the failure mechanism, and the acoustic emission parameters of the anchored joints are studied under different surface roughnesses and anchorage conditions. The shear strength and residual strength increase with the roughness of the anchored joint surface. With an increase in bolt elongation, the shear strength of the anchored joint surface gradually decreases. When the anchored structural plane is sheared, the ideal cumulative impact curve can be divided into four stages: initial emission, critical instability, cumulative energy, and failure. With an increase in the roughness of the anchored joint surface, the peak energy rate and the cumulative number of events will also increase during macro-scale shear failure. With an increase in the bolt elongation, the energy rate and the event number increase during the shearing process. Furthermore, the peak energy rate, peak number of events and cumulative energy will all increase with the bolt elongation. The results of this study can provide guidance for the use of the acoustic emission technique in monitoring and predicting the static shear failure of anchored rock masses.

Experimental Study on Effect of Waste Plastic Bottle Strips in Soil Improvement

Abstract: With rapid advancements in technology globally, the use of plastics such as polyethylene bags, bottles etc. is also increasing. The disposal of thrown away wastes pose a serious challenge since most of the plastic wastes are non-biodegradable and unfit for incineration as they emit harmful gases. Soil stabilization improves the engineering properties of weak soils by controlled compaction or adding stabilizers like cement, lime etc. but these additives also have become expensive in recent years. This paper presents a detailed study on the behavior and use of waste plastic in soil improvement. Experimental investigation on reinforced plastic soil results showed that, plastic can be used as an effective stabilizer so as to encounter waste disposal problem as well as an economical solution for stabilizing weak soils. Plastic reinforced soil behaves like a fiber reinforced soil. This study involves the investigation of the effect of plastic bottle strips on silty sand for which a series of compaction, direct shear and California bearing ratio (CBR) tests have been performed with varying percentages of plastic strips and also with different aspect ratios in terms of size. The results reflect that there is significant increment in maximum dry unit weight, Shear Strength Parameters and CBR value with plastic reinforcement in soil. The quantum of improvement in the soil properties depends on type of soil, plastic content and size of strip. It is observed from the study that, improvement in engineering properties of silty sand is achieved at 0.4% plastic content with strip size of (15 mm × 15 mm).

Experimental and phenomenological study of the effects of adding shredded tire chips on geotechnical properties of peat

Abstract: Due to the high values of organic and water contents, and other poor geotechnical properties of peats, it is essential to stabilise peat deposits. Moreover, in recent decades, accumulation of waste tires has caused myriad environmental problems all around the world. To tackle both issues, a reasonable remedy is to use scrap tires for stabilisation of peat soils. Since some of geotechnical properties of tire stabilised peats have been not reported yet, the aim of this study is to investigate the effects of adding different weight percentages of shredded tire chips (0, 5, 10, 15 and 20%) along with constant amount of sand (400 kg/m3) on some of geotechnical properties of stabilised peat such as unconfined compressive strength (UCS), secant modulus (Es), failure strain (ef), brittleness index (IB), deformability indexes (ID), resilient modulus (Mr), bulk modulus (K), shear modulus (G), cohesion (C) and angle of internal friction (φ) using UCS and direct shear tests. Moreover, to chemically characterise sand ...

Determination of the shearing behaviour of root-permeated soils with a large-scale direct shear apparatus

Abstract: Soils with roots or root-like inclusions have often been tested in direct shear to quantify the effects of vegetation on the shear strength of soil, and in turn, the stability of slopes. However, a straightforward evaluation of root reinforcement is challenging due to the complex nature of roots, and the dependency of soil behaviour on many factors. An Inclinable Large-scale Direct Shear Apparatus (ILDSA) was built to study the shearing behaviour of root-permeated soils. Planted specimens, consisting of two different sets of species, were prepared with a moraine, sampled from a recent landslide location, and tested in direct shear subsequent to saturation. Relationships of peak stress ratio with dry weight of roots, maximum dilatancy angle and void ratio were investigated to evaluate the behaviour of root-permeated soil. The combined approach, of taking both presence of roots and dilatant behaviour of soil into consideration, results in a more realistic understanding and quantification of the effects of root reinforcement, at least, for laboratory testing of root-permeated soils.

Evaluating the influence of ballast degradation on its shear behaviour

Abstract: The main goal of this research is to investigate the effect of ballast degradation on its shear strength behaviour. For this purpose, some crushing tests were carried out at different compressive l...

Effect of fiber reinforcement on shear strength and void ratio of soft clay

Abstract: In this study, a series of multi-stage drained reverse direct shear tests were carried out on soft clay samples reinforced with 0.25% and 0.50% polypropylene fibers of 6 mm, 10 mm and 19 mm in leng...