Decrease In Shear Strength Research Articles

Numerical study using FE simulation on rectangular RC beams with vertical circular web openings in the shear zones

Transverse and vertical openings are usually created in beams made of reinforced concrete (RC) to accommodate the pipes and ducts used in utilities. The decrease in shear strength because of the openings causes problems in current RC beams. This study investigates the impact of various vertical circular web openings alongside the shear-area span of an RC beam on its shear performance. To this end, a model with three finite element (FE) dimensions was developed, primarily for investigating and analyzing the outcome of this case. Using the ANSYS-V15 FE program, 41 beams were analyzed. The findings of the eight investigational beams were compared with results from previously published works. The devised model was tested to ensure its accurate functioning, using outcomes already attained through experiments. The outcomes of the experimental test proved that the newly devised FE model could be used to calculate the RC beams’ shear-load capacity and to accurately predict failure modes. The outcomes revealed that the effect of the vertical-opening diameter on the width of the beam section was greater than the effect of the length of the shear span. Therefore, we concluded that the influence of the opening diameter was greater than the effect of the number of openings.

Influence of Intermittent Artificial Crack Density on Shear Fracturing and Fractal Behavior of Rock Bridges: Experimental and Numerical Studies

Shear-box experiments, Rock Failure Process Analysis (RFPA) simulations, and box-counting fractal analysis on rock-like models are conducted to investigate the influence of intermittent artificial crack density on the shear fracturing and fractal behavior of rock bridges in jointed rock slopes. The artificial crack geometry of the conceptual rock bridge model is a combination of two edge-notched artificial cracks and imbedded artificial cracks with different intermittent artificial crack densities. By numerical shear-box tests, deep insight into the mesoscopic mechanism of crack evolution is gained, and the simulated failure patterns are in accordance with experimental results. Three types of failure patterns are identified: shear mode, mixed shear/tensile mode, and tensile mode. The RFPA simulations demonstrate that macroscale shear cracks form as damage belts consisting of many tensile/shear mesocracks, as typically observed in microscopic experimental work. The failure pattern is mostly influenced by the intermittent artificial crack density, whereas the peak shear strength is related to the failure pattern. As the intermittent artificial crack density increases, the failure pattern changes from shear mode to mixed shear/tensile mode and then to tensile mode, resulting in a decrease in the peak shear strength. The regression analysis shows that the relationship between the peak shear strength and intermittent artificial crack density can be expressed by an exponential decay model. Furthermore, digital image processing and box-counting fractal analyses are performed on the shear fracture surfaces of the physical and numerical models to describe the fractal behavior. The relationships between the fractal dimension and peak shear strength are analyzed, and strong correlations that display an exponential decay function are found.

The Relevancy of Mineral Composition to Rock Shear Strength in Kaliwadas Hills, Karangsambung, Kebumen

The occurrence of landslides on the slopes due to a decrease in shear strength in the area of landslides in the limestone hills of Kaliwadas, Kebumen, Central Java, causes public facilities to be damaged and disrupting the activities of everyday citizens. Factors that influence rock shear strength are cohesion value and internal friction angle, while mineralogy and grain size is one of the factors derived from the environment which also affects the shear strength value. This study aims to determine the effect of mineral composition and grain size on rock shear strength. A number of rock samples were taken from the study site to be prepared, cylindrical samples for direct shear and petrographic strength tests with thin incision samples. Direct shear test results provide cohesion values and deep shear angles in limestone with peak and residual conditions of 0.22 Mpa and 39.73 ° respectively; 36.61 kPa and 29.28 ° while in claystone 67.86 kPa and 25.36°; 13.41 kPa and 16.17 °. Petrographic analysis of rocks shows that limestone contains calcite (88%) and quartz minerals (5%), while claystone contains calcite (91%) and quartz minerals (2%). Based on the mineral content of limestone and claystone and their effect on rock shear strength, it can be concluded that limestones have a quartz mineral composition, cohesion values and deep shear angles that are better and larger when compared to rock shear strength in claystone and believed to be the cause of the slip field in the research location.

Investigation of damage behaviors of ECC-to-concrete interface and damage prediction model under salt freeze-thaw cycles

This paper reveals an investigation of damage behaviors of ECC-to-concrete interface with various ECC strength grades and interface roughness of concrete substrate subjected to salt freeze-thaw cycles. The test results showed that salt freeze-thaw cycles had significant negative influences on bonding behaviors of ECC-to-concrete interface. The occurrence of interface fracture and degradation of interface shear strength under salt freeze-thaw cycles could be significantly influenced by ECC strength grade and interface roughness of substrate concrete. The lower ECC strength and the smoother interface always caused earlier occurrences of interface fracture under salt freeze-thaw cycles. Besides, the lower ECC strength and the smoother interface always caused earlier occurrences of a sharp decline of interface shear strength and more decrease of interface shear strength. The area erosion rate of interface under salt freeze-thaw cycles could be significantly influenced by interface roughness of substrate concrete, and the smoother interface always caused more area erosion rate of interface. Based on the micro-damage mechanism of ECC-to-concrete interface under salt freeze-thaw cycles, a damage prediction model of ECC-to-concrete interface was proposed in this paper. The model is expected to be used to predict the damage degree of ECC-to-concrete interface subjected to salt freeze-thaw cycles.

Slope failure induced by cold snap and continuous precipitation in the seasonal frozen area of Qinghai-Tibet Plateau

A slope failure of roughly 26,000 m3 occurred on September 7th, 2017 in the upper layer of a north-facing slope at Autumn Pasture in Zhimei Village, Chenduo County, Tibetan Autonomous Prefecture of Yushu (34°07′02.26″N, 96°37′10.90″E). Field investigations have indicated there is no continuous or discontinuous permafrost found in this area. The earth slope is susceptible to seasonal frost in freezing season and heavy rainfall in raining season. Hence, we hypothesized that the slope failure was induced by increasing pore water pressure at the basal surface, which resulted from the combined effect of a frozen upper layer and accumulated infiltrated soil water. With the accessible meteorological data from National Oceanic and Atmospheric Administration (NOAA), numerical software (CoupModel) was used to simulate the hydro-thermal state of the source area in order to explore the influence of atmospheric change and the triggering mechanism of slope failure. The simulation results indicate that an unexpected cold snap promoted the freezing process of the shallow soil layer, and the drainage of liquid water was impeded by this frozen layer. Accumulated downslope water at source area, namely the slope toe, led to the increasing of pore water pressure in the deeper parts of the soil. The source area is located in the catchment area, where water accumulated from surrounding slopes. Increased gravity of the upper layer resulting from downslope infiltrating soil water, and decreased shear strength of basal surface both contributed to the slope instability. The failure illustrated the influence of seasonal frost and sustained precipitation on mass wasting in Qinghai-Tibet Plateau (QTP).

ASSESSMENT OF SHEAR BOND STRENGTH OF RESTORATIVE MATERIALS IN VARIOUS DEPTH OF HARD DENTAL TISSUE PREPARATION IN FRONT TEETH

In modern dentistry, there are two different approaches to the restoration of anatomy and aesthetics of anterior teeth. The most common is the option of direct restoration with using composite resin materials. The second option is the restoration with using ceramic materials that is carried out through the cooperation of the dentists and the dental laboratory technicians, or, alternatively, with various CAD-CAM systems directly at the dental office. This experiment was carried out by using teeth (premolars, incisors) without significant loss of hard dental tissues. Teeth with abrasion (all except 1st degree) were excluded from the test group. Within the framework of the planned study, the selected extracted teeth were prepared (a certain volume of hard tissues was removed from the vestibular side (a subgroup of the teeth prepared within in the enamel layer, and a subgroup of teeth with the exposed dentine). A total of 40 teeth were prepared (20 teeth with the exposed dentine, 20 with the enamel preparation). The tests were carried out by using a universal testing machine AUTOGRAPH AGS-J. A sample with a tooth was placed at the top of the device then the second part of the sample containing the plate of the material (composite or ceramic), was covered with the second part of the device to be tested, and neatly, trying to avoid applying tension to the adhesive butt joints, and then fastened to the lower clamping device of the tension testing machine. We created the shear forces before the sample was destroyed, paying attention to the character of adhesion line oddments. The results of the experiment have demonstrated that the most optimal shear strength is found out in the complex of hard tooth tissues and ceramic materials IPS Empress Aesthetic and EX3, in the teeth prepared within the tooth enamel layer. When using composite resin, the values studied are lower by 11,4% and 18,1%, (application of adhesion systems of 5th and 7th generations, respectively). In the cases when dentin is exposed, the shear strength decreases by 19,5% when using ceramics modified by leucite glass, by 17,3% in the case of application of feldspar ceramics, and by 8,4% and 13,2% for composite resin restoration when using adhesive systems of 5th and 7Ith generations respectively.

INFLUENCE OF EXPOSURE TIME TO OPERATING TEMPERATURE ON SHEAR STRENGTH OF WOOD USED IN ROOF STRUCTURES

ABSTRACT Wood is one of the main materials used in the constructing of covering structures (roofs) because of its versatility. Under this situation, due to solar radiation incidence, the temperature can exceed 60 °C and, such as other environmental conditions, influence the mechanical properties of the wood in use. The aim of this research was to study the influence of exposure time of the wood of four different hardwood species at a temperature of 60 °C on the shear strength parallel to fibers. The wood of the following species was used: Cupiuba (Goupia glabra), Eucalyptus (Eucalyptus saligna), Garapeira (Apuleia leiocarpa), and Jatoba Tamarindo (Hymenaea sp.). In order to investigate the effect of exposure time (0, 168, 456, 720, and 2160 hours) of the wood species in an oven (60 °C) on the values of shear strength in the direction parallel to fibers, an analysis of variance (ANOVA) was carried out at 5% significance level. According to the results, the time the wood was exposed to the operating temperature significantly influenced the shear strength in the direction parallel to fibers. In addition, all species showed a decrease in shear strength after 456 hours of exposure at a constant temperature of 60 °C.

Effect of Cu, Ag on the microstructure and IMC evolution of Sn5Sb–CuAgNi/Cu solder joints

In this paper, three new type Sn5Sb-based solders were used to the study. The three sets of solders are Sn–5Sb–0.5Cu–0.1Ni–0.5Ag, Sn–5Sb–0.5Cu–0.1Ni–0.1Ag and Sn–5Sb–1Cu–0.1Ni–0.1Ag. Experimental results indicated that with the increase of Cu and Ag, the solidus temperature reduced due to the increase of the eutectic phase of low melting point Ag3Sn+β-Sn and Cu6Sn5+β-Sn in the solder. The adding elements of Cu, Ni, Ag can improve the wettability of Sn5Sb while excessive Cu, Ag content inhibit the wettability. The Similar microstructures exist in the three groups of solders, which consist of β-Sn–Sb solid solutions, (Cu1−xNix)6Sn5, Ag3Sn and a small amout of β-Sn. The interfacial intermetallic compound (IMC) is composed of (Cu1−xNix)6Sn5. The lower Cu content suppresses the IMC growth by increasing the dissolution of interfacial IMCs into bulk solder but it also increase the IMC growth by elevating the diffusion speed. The thickness of the IMC layer of Sn–5Sb–0.5Cu–0.1Ni–0.1Ag/Cu grow faster than that of Sn–5Sb–1Cu–0.1Ni–0.1Ag/Cu, Which illustrates the Cu atoms affect the IMC mainly through inhibiting the reaction diffusion. The addition of Ag in the solder significantly suppressed the IMC layer in Sn–5Sb–0.5Cu–0.1Ni–0.5Ag/Cu, Which is attributes to the concentration of Ag3Sn near the IMC layer. The increase of Cu, Ag content in the solder will increase the ductility of the solder. The toughness decrease when the liquid keeping time over 30 s and the shear strength decrease correspondingly. The fracture mechanism changed from ductile fracture to tough and brittle hybrid fracture when the liquid keeping time from 10 s to 90 s.

Shear strength between Sn–3.0Ag–0.5Cu solders and Cu substrate after two solid-state aging processes for fan-out package process applications

Shear strength between Sn–3.0Ag–0.5Cu (SAC) solders and Cu/Ti in under bump metallization (UBM) samples aged using two solid-state aging processes was investigated. One method aged the samples at 200 °C for up for five 1-h intervals; the other aged the samples at 200 °C continuously for up to 5 h in a convection oven. After reflow, all samples showed scallop-shaped Cu6Sn5 intermetallic compounds (IMCs) at the interfaces between SAC solder and Cu substrate. After aging, the Cu layers of all samples were gradually depleted, and lump-shaped Cu6Sn5 was observed to be separated from the SAC/Cu interfaces. The shear strength of all samples was gradually decreased with increased aging due to depletion of the Cu wetting layer, formation of IMCs with solder, and separation of the IMCs from the interfaces during aging. Quantitative analysis revealed that exposed Ti area is an effective predictor of decrease in shear strength generated by the spalling phenomenon.

Tension‐shear interaction of high‐strength bolts during and after fire

AbstractConnections in steel structures play an essential role in the structural stability of the entire construction. This is also true in the event of a fire. The difficulty in designing connections for fire lies in the fact that not only material properties, but also loads applied to the connections change depending on temperature. In addition, the temperature‐dependent decrease in the tensile strength of high‐strength bolts does not coincide with the decrease in shear strength. So far, the influence of combined tension and shear loading on high‐strength bolts has not been studied in detail.This project included carrying out interaction tests on high‐strength bolts of property class 10.9 (fu = 1000 N/mm2). Post‐fire performance was examined in addition to observing the loadbearing behaviour during fire. The examinations were completed with additional material tests. The results were compared with earlier research on the temperature‐dependent loadbearing capacity of high‐strength bolts during and after temperature loading as well as on the loadbearing behaviour of bolts in steel structures under combined tension and shear loads. This investigation contributes to a better understanding of the loadbearing capacity of high‐strength bolts under combined loading during and after a fire.

Effect of Repetitive Collar Replacement on the Residual Strength and Fatigue Life of Retained Hi-Lok Fastener Pins

Hi-Lok fasteners were subjected to multiple collar replacements, and were tested under static loading and constant-amplitude fatigue loading, to determine the effect of repetitive collar replacement on the residual strength and fatigue life of a retained Hi-Lok-type fastener pin. Hi-Lok-type fasteners are typically used in aircraft structural joints, and are loaded mainly in shear. Tests were conducted for clamping force, static shear strength, static tensile strength, and shear fatigue life for collars subjected to five collar replacements. The static shear results showed no decrease in the ultimate shear strength of the fastener pin as a function of collar replacement. Static tensile results showed no decrease in the ultimate tensile strength of the fastener as a function of collar replacement, with failure of the aluminum collar remaining the critical failure mode. Similarly, shear fatigue results showed no decrease in the shear fatigue life of the fastened joint as a result of collar replacement, with fracture of the aluminum substrate remaining the critical failure mode. For static shear, static tension, and shear fatigue tests, estimated clamping force was highly consistent between specimens and no decrease in clamping force was observed as a function of collar replacement.

Frictional weakening of slip interfaces.

When two objects are in contact, the force necessary to overcome friction is larger than the force necessary to keep sliding motion going. This difference between static and dynamic friction is usually attributed to the growth of the area of real contact between rough surfaces in time when the system is at rest. We directly measure the area of real contact and show that it actually increases during macroscopic slip, despite the fact that dynamic friction is smaller than static friction. This signals a decrease in the interfacial shear strength, the friction per unit contact area, which is due to a mechanical weakening of the asperities. This provides a novel explanation for stick-slip phenomena in, e.g., earthquakes.

Combined effects of temperature, hydraulic pressure and salty concentration on the water uptake and mechanical properties of a carbon/glass fibers hybrid rod in salty solutions

Pultruded unidirectional large-diameter (19 mm) carbon/glass fiber hybrid rods were used to investigate the coupling effects of elevated temperature and hydraulic pressure on water uptake and mechanical properties in salty solutions. Salty solutions with different salty concentrations at 60 °C and 80 °C with and without a hydraulic pressure of 20 MPa were selected as immersion media and the hybrid rods were immersed for half of a year. A self-designed hydraulic pressure device was applied for immersion and a new testing device was designed to obtain the interface shear strength (ISS) of the fiber and epoxy. Radial and longitudinal water uptakes of the hybrid rods were found to follow the classic Fick law. Elevated temperature and hydraulic pressure accelerated the diffusion of water molecules; while the salty concentration exhibited a negligible effect. The radial diffusivity in the hybrid rods was larger than longitudinal diffusivity due to the absence of “fiber barrier action”. Elevated temperatures led to an obvious decrease in the interface shear strength of the glass fiber shell, carbon fiber core, and shell–core interface. The interface shear strength of the shell–core interface was most susceptible to the immersion, and long-term stable retention was predicted to be ~54.2%, regardless of the immersed temperature and hydraulic pressure.

A Study on the Laterally Loaded Pile Behaviour in Liquefied Soil Using P-Y Method

Under repeated seismic loads during an earthquake, increase of pore water pressure in cohesionless, saturated and loose soils leads to decreased shear strength and therefore liquefaction occurs. Literature reports of numerous cases involving damage due to liquefied soil which makes the pile behaviour and performance in liquefied soil even more important. It is possible to investigate the behaviour of piles located in the liquefied soil under inertial loads using linear spring model, p-y method or numerical analyses and a suitable liquefaction constitutive model in time. This study investigates the behaviour of two piles, located in the foundation of the “Niigata Family Courthouse” which was damaged during the Niigata earthquake of 1964, under inertial loads in liquefied soil. The soil profile identified for this case and the piles are analyzed using p-y method and linear spring approach. Pile deformations and bending moments calculated with these two methods were compared.

The effect of phenol-formaldehyde adhesive modification with fire retardant on the properties of birch plywood

The effect of phenol-formaldehyde adhesive modification with fire retardant on the properties of birch plywood. The study investigated how the modification of phenol-formaldehyde adhesive with a mixture of potassium carbonate and urea affect the properties of plywood. Based on the investigations of the viscosity, gel time and solid content of PF resin mixture containing various amounts of modifiers with various compositions it was found that modification led to major decrease in viscosity, caused the elongation of gelling time and reduced the solid content. In all variants modification of the resin led to significant improvement in plywood flammability evaluated on the basis of parameters such as: weight loss, time of ignition and burned area. The addition of fire retardant to the resin caused a decrease of shear strength. Composition of the modifier had a significant effect on bonding quality, however all plywood samples retained good values exceeding 1 N/mm2 required by EN 314-2 (1993).

Degradation Mechanisms of SiC/BN/SiC after Low Temperature Humidity Exposure

The environmental degradation of SiC/BN/SiC CMCs under low temperature water exposure is still an unexplored field. This work shows how the effect of low temperature humid environments can be detrimental for amorphous BN interfaces, leading to a drop in mechanical properties. Furthermore, initial low-temperature humid environments can induce a faster degradation during subsequent thermal exposure. In order to understand how low temperature water exposure affects the CMC and how these changes affect the material response to subsequent exposures, intermediate temperature (800°C) exposures have been studied before and after the low temperature humidity tests. The main challenge of this work consists of understanding how different constituents of the CMC structure (e.g. fibres and interfaces) are degrading and consequently affecting the overall bulk mechanical performance and failure modes of the material. For this, linking the change in morphology and chemistry of the interfaces with the micromechanical properties of the individual constituents has been crucial. STEM-EDS has shown a change in morphology of the BN interface after the low temperature water exposure, which has been linked to a decrease in interfacial shear strength and friction (measured via in-situ fibre push-out tests) of ≈ 90%. STEM-EELS has shown how, after the interfaces have been exposed to the humidity as well as to subsequent intermediate temperatures in the presence of the remaining BN, induces degradation of the SiC fibres which results in a tensile strength reduction of ≈ 25% (measured via in-situ 3-point bending of individual fibres). These results provide a new insight into how low temperature water exposures must be considered in future degradation studies of CMCs. Additionally, we propose a new methodology to fundamentally understand the complex failure modes of CMCs.

Evaluation of Undrained Bearing Capacities of Wide‐Shallow Bucket Foundation with Honeycomb Bulkheads in Clay

As a new type of offshore wind foundation, the wide‐shallow bucket foundation with honeycomb bulkheads mainly bears vertical, horizontal, and moment loads. As yet, no systematic study has been conducted regarding the effects of honeycomb bulkheads on the undrained bearing capacities of the wide‐shallow bucket foundation. In this study, a large number of three‐dimensional (3D) finite element (FE) analyses were performed to investigate the undrained bearing capacities of the wide‐shallow bucket foundations with and without honeycomb bulkheads, thereby evaluating the influence of honeycomb bulkheads on the bearing capacities under different conditions. The results show that under uniaxial loading, the uniaxial bearing capacities of the wide‐shallow bucket foundation are basically unaffected by the honeycomb bulkheads in homogeneous clay. For nonhomogeneous clay, the moment bearing capacity will be considerably enhanced with the increase in soil shear strength heterogeneity. Under combined loading, the honeycomb bulkheads will enhance the combined bearing capacities only in nonhomogeneous clay. The enhancement effects will increase with the increase in soil shear strength heterogeneity but decrease with the increase in vertical load. Besides, the simplified equations for calculating the uniaxial bearing capacities of the wide‐shallow bucket foundation with honeycomb bulkheads are also proposed considering the influence of embedment ratio and soil shear strength heterogeneity. At last, the parameters of an approximating expression are fitted to predict the failure envelopes of this foundation under combined loading.

Effect of long-term thermal cycling and moisture on heated Fibre Metal Laminates and glass-fibre epoxy composites

Heated GLARE, a Fibre Metal Laminate with an integrated heater element, has a promising potential as de- or anti-icing system in aircraft structures. To investigate the long-term durability of heated GLARE previously reported thermal cycling tests up to 12,000 cycles are extended up to 144,000 cycles and moisture conditioning is included. Similar testing up to 72,000 cycles is performed on FM906 glass-fibre epoxy laminates with an integrated heater element to study the influence of the aluminium layers in GLARE.In all test results the initial decrease in interlaminar shear values from 0 to about 10,000 thermal cycles is followed by a recovery phase and a resumed decline after roughly 60,000 cycles. The decrease in ILSS is expected to be caused by internal stress relief which is counteracted by the positive effect of physical ageing due to elevated temperature exposure. Thermal cycling of conditioned samples generally resulted in slightly larger decreases in interlaminar shear strength for both heated GLARE and heated FM906 glass-fibre epoxy laminates.

The study of adhesion between steel substrate, primer, and char of intumescent fire retardant coating

The aim of this study was to characterize the adhesion bonding of intumescent coating and the primer on steel substrate with respect to its mechanical, physical and chemical properties, before and after a fire test. The coated steel substrates were subjected to fire in a furnace at 950 °C for various durations ranging from 30, 45, and 90 to 120 min. The coatings were characterized by Thermogravimetric Analysis (TGA) while the char from fire test was characterized by Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR). For mechanical properties, the shear strength of the intumescent coating was measured for various coating thicknesses ranging from 1, 2, 3, 4, 10 to 22 mm through lap shear test. The changes in the adhesion bonding of the coatings, primer, and char with steel substrate microstructure were monitored using SEM. The microstructure observation indicated a profound mechanical interlocking mechanism between the primer coating and the steel substrate. Despite the two-hour fire test, the temperature of the steel substrate remained below 100 °C and no re-crystallization was observed. A considerable decrease in shear strength of the intumescent coating, primer and steel substrate from 1.95 MPa to 0.23 MPa was also measured as the thickness of the coating substrate was increased from 1 mm to 22 mm, respectively.

Development and application of an instrument for simulating wetting-drying cycles of expansive soils under loads

Alternating rainfall and evaporation in nature severely impact the shear strength of expansive soils. This study presents an instrument for simulating the effect of wetting-drying cycles on the strength of expansive soils under different loads, and its testing error is verified. With this instrument, direct shear tests were performed on samples experiencing 0–6 cycles under vertical loads of 0 kPa, 5 kPa, 15 kPa, and 30 kPa. The results found that this instrument provides a new method for evaluating the effects of wetting-drying cycles on soils, and this method represents actual engineering conditions more accurately than do preexisting methods. It accurately controls the water content within 1% while simulating the specified loads at different soil depths. Cohesion is significantly affected by wetting-drying cycles, while the friction angle is not as sensitive to these cycles. Decrease in shear strength can be attributed to the fissures in soils caused by wetting-drying cycles. The existence of vertical loads effectively restricts shrinkage fissuring and cohesion attenuation, consequently inhibiting the attenuation of shear strength.