Improvement In Shear Strength Research Articles

Investigating the combination effect of warm extrusion and multi-directional forging on microstructure and mechanical properties of Al–Mg2Si composites

The combined effect of extrusion and multi-directional forging (MDF) was investigated on microstructure and mechanical properties of aluminum-based composite with 10, 15, and 20 wt% Mg2Si. In the casted Al–Mg2Si composites, the primary and eutectic Mg2Si particles are generally coarse which lead to decreasing their mechanical properties and formability. Extrusion process was utilized to overcome this shortcoming by breakage of the eutectic structure, reduction of Mg2Si size, and the decrease of casting defects. Then, MDF process was applied up to failure on the extruded composites at room temperature. It led to the morphological modification of primary and eutectic Mg2Si phases and the reduction of their size. It was found that the MDF process resulted in a considerable improvement in hardness and shear strength of materials. This may be related to the reduction in the average size of Mg2Si particles with their uniform distribution. In addition, ultimate shear strength is, respectively, increased from 94, 99, and 81 MPa to 119, 116, and 117 MPa for the 10, 15, and 20 wt% Mg2Si aluminum composites after the final pass of MDF. Meanwhile, the normal displacement of composites is reduced at initial passes and increased by the addition of more pass numbers.

Enhanced interfacial strength of hierarchical fiberglass composites through an aramid nanofiber interphase

Interfacial adhesion in fiber reinforced composites is a critical factor for their mechanical performance in structural applications. As nanomaterials continue to rise in prominence, the use of nanostructured interphases has grown to become a viable technique to reinforce the fiber-matrix interface of fiber reinforced polymer composites. Here, a polymeric interphase consisting of aramid nanofibers (ANFs) is introduced on Poly(diallyldimethylammonium chloride) (PDDA) coated fiberglass through electrostatic adsorption. The simple and rapid coating technique considerably roughens the inorganic fiber surface, while enriching it with polar functional groups that are capable of chemically bonding with the matrix, all while preserving the structural integrity of the fiber. The nanostructured coating improves the interfacial shear strength by up to 83.2%, along with a 35.3% improvement in short beam shear strength. These improvements can be attributed to the enhanced chemical and mechanical interactions between the fiber and the matrix. The following findings highlight the potential for the utilization of a PDDA coating to enhance the adhesion of ANFs on fiberglass and enable the fabrication of composite structures with higher strength and toughness through a rapid, simple and effective surface treatment.

Critical Insights in the Application of Convection and Pressure Curing in Eliminating DAF Voids

The absent of reliable production controls for Die Attach Film (DAF) voids detection allowed defect escapee for Ball Grid Array (BGA) devices using non-conductive film material leading to gross assembly rejection and customer complaints. This paper presents the evaluation of pressure curing as an alternative to the convection curing in die attach process with additional capability to eliminate the DAF voids on non-conductive films. Through Analysis of Variance (ANOVA) analysis, green peeling test, Scanning Acoustic Microscope (SAM), cross section analysis and reliability test performed between samples arrives to the conclusion that pressure oven has a significant impact in die shear strength improvement and DAF voids elimination with positive response in reliability requirement. The result of the study improves the assembly flow and production control of BGA devices through the transition of convection to pressure curing technology.

A sequential design approach for in situ incorporation of cellulose nanocrystals in emulsion-based pressure sensitive adhesives

Cellulose nanocrystals (CNCs) are naturally-sourced nanoparticles that can be used to modify polymers and provide exceptional mechanical properties to nanocomposite materials. In this study, CNCs were incorporated into water-based pressure sensitive adhesives (PSAs) via in situ semi-batch emulsion polymerization to improve PSA properties. A sequential design approach was used to improve CNC/poly(n-butyl acrylate/vinyl acetate) nanocomposite PSAs. In the first part of the design, the effects of acrylic acid (AA) and anionic surfactant sodium dodecyl sulfate (SDS) were examined in the presence of 0.5 wt% CNCs (based on polymer mass). While the SDS was crucial to maintaining latex stability, its excessive addition led to a decrease in PSA performance, namely tack and peel strength. The AA comonomer was pivotal in improving the shear strength of the PSAs, especially in the presence of CNCs. In all cases, the addition of CNCs led to improved PSA shear strength. In the second part of the design, the addition of 1-dodecanethiol (NDM) as a chain transfer agent (CTA) with CNC levels up to 1 wt% led to an improvement in tack and peel strength but at the cost of diminishing the shear strength. Generally, the addition of CNCs improved PSA performance. Thus, to maximize the impact of CNCs on PSA properties, a careful balance of SDS (for latex stability), AA (to improve shear strength) and NDM (to improve tack and peel strength) are needed.

Ultrastable and Durable Silicone Coating on Polycarbonate Surface Realized by Nanoscale Interfacial Engineering.

Delamination of coating layer from polymer substrate limits the lifetime and functionality of the protective films. Silicone coating is especially vulnerable to photo irradiation, hydrothermal degradation, and mechanical deformation due to the low interfacial adhesion and mechanical robustness. Herein, an ingenious approach is developed to fabricate ultrastable and durable silicone coating on polycarbonate (PC) substrate through well-controlled nanoscale interfacial engineering. A nanopillar array is fabricated on the PC surface by vacuum-assisted hot embossing using anodic aluminum oxide (AAO) templates. Significant improvement in interfacial shear strength (ISS) is achieved for the silicone coating on the nanostructured PC surface. The delamination mechanism can be controlled by tuning the nanopillar size, and the maximum ISS of 9.9 MPa was reached on a surface with a nanopillar diameter of 320 nm. Attributed to the increased interfacial area and mechanical interlocking structure, the nanostructured interface can effectively dissipate interfacial stress and prevent cracking; therefore, maintaining excellent transparency and performance in the harsh environment. The coating exhibits extraordinary stability and durability when subjected to UV irradiation for 168 h, hydrothermal aging for 120 h, mechanical bending for 1000 cycles, and even surface damage. Thus, the tough silicone coating on polymer substraterealized by nanoscale interfacial engineering is a promising technique for highly stable and durable transparent surface protection.

Improved adhesion between stainless steel heating element and PPS polymer in resistance welding of thermoplastic composites

Resistance welding of thermoplastic composites involves applying an electric current to a heating element, usually a stainless-steel (SS) mesh, which heats up by Joule effect, melts the surrounding polymer matrix and remains at the joint interface following the welding operation. In this study, the adhesion between a thermoplastic matrix, i.e., polyphenylene sulfide (PPS), and the SS mesh heating element is evaluated and improved through the application of surface coatings on the SS. The coatings are based on an organosilane, a bivalent molecule often used to create an organic coating on metals. The efficiency of the surface coatings is evaluated by measurement of the water contact angle on treated SS plates, characterization of the coating by ATR-FTIR, observations by SEM and TEM and mechanical testing of resistance-welded quasi-isotropic carbon fibre (CF)/PPS joints. A lap shear strength (LSS) improvement of 32% is reported for joints welded using the treated heating elements relative to joints welded using untreated heating elements. Double cantilever beam tests between a SS plate and the CF/PPS composite also show a much better adhesion between the PPS and SS following surface coating, with a higher load at failure and fracture surfaces showing polymer and fibre remaining attached to the SS plate.

Quasi-static and Dynamic Lap Shear Strength of Aluminium Joints Bonded with Epoxy/Alumina Nanocomposite Adhesive

Quasi-static shear strength of aluminium alloy single lap joints was determined as a function of wt% (0.5, 1.0, 1.5, and 2.0) of spherical and rod shaped nanoalumina in epoxy adhesive under compressive loading. Static shear strength for nanoadhesive containing 1.5 wt% of nanoparticles (for both spherical and rod shaped nanoalumina) was observed to be maximum. Dynamic shear strength for neat adhesive and nanoadhesives containing 1.5 wt% of spherical and rod shaped nanoalumina were analysed at two different loading rates using a split Hopkinson pressure bar system. A significant improvement (3 to 7 times) of dynamic shear strength of joints was perceived over static shear strength of joints. Static and dynamic lap shear strength for nanoadhesive containing nanospheres were significantly more than that for neat adhesive and nanoadhesive containing nanorods.

Experimental study of the mechanical effect of a clayey soil by adding rubber powder for geotechnical applications

At present, worrying quantities of tires are discarded due to the growth in demand for vehicles in the world, which has a direct impact on the deterioration of the environment since they normally go to landfills. Based on the background found, the use of this material for geotechnical applications can help reduce the pollution they generate and improve the physical and mechanical properties of soils. Therefore, this research seeks to evaluate a greater shear strength and capacity of support to the penetration of the clayey soil by means of the addition of 1.5%, 2.5% and 3.5% of rubber powder recycled. For this, the Atterberg limits analysis, the modified proctor compaction test, shear box and CBR were performed. For the shear box test, the results reflect that the cohesion of the mixture increased and the angle of internal friction decreased with respect to the natural soil, resulting in the sum in an increase of shear strength. On the other hand, the percentage of CBR increased, this means that the rubber helped the soil to be more rigid and have a greater resistance to penetration. These mixtures could be used in different projects within geotechnical engineering, as it presents an improvement in shear strength and an acceptable support index value (CBR).

Punching shear strength of flat slabs strengthened with internal flexible CFRP patches

This paper presents a strengthening method used for improving the punching shear strength of flat slabs. Square internal patches of carbon fiber reinforced polymer were placed at the center of 450×450mm fresh concrete slabs, through casting, at a distance from the bottom (tension) face, producing four specimens. The dimensions of these patches were from 60×60mm to 200×200mm. The results have shown that the strengthened specimens had higher punching shear strength in comparison to the control specimen, with an increasing rate ranging from 15 to 45 %. In addition to the sensibly improved shear strength, this strengthening method is capable of changing the mode of failure from combined flexural-punching to pure punching shear failure.

An investigation into the effects of block size on the mechanical behaviors of bimsoils using variable-angle shear experiments

Shear resistance is critical to the stability of bimsoils (block-in-matrix soils), although the shear mechanical behaviors of bimsoil have been widely studied, the effect of rock block size on the rock–soil interactions, block occlusion and the interlocking effect during shearing are still not well understood. This work aims to investigate the effect of block size on the macro–meso shear failure mechanism of bimsoils using a specially designed variable-angle shear testing. Compaction test with different hammer counts was used to prepare the bimsoil samples having different rock block proportions and sizes, to roughly ensure the same compactness of soil matrix. Macroscopic shear force–displacement analysis combined with the mesoscopic 3-D laser technique was used to reveal the internal shear failure mechanism. The results show that block size has obvious effect on the shear strength parameters and morphology of shear failure plane. The peak shear force increases with the increase of block size, and the occlusion and interlocking phenomena become severe for the sample with relatively large block size. An index of fractal dimension was used to establish the relationship between block size and shear strength parameters, it suggests that the fractal dimension of the fracture surface is large for the samples having larger block size, and the shear strength of bimsoil is strongly related to the morphology of fracture surface. The improvement of shear strength for bimsoil was the results of interactions between soil matrix and rock blocks and induced by the intrinsic shear fracture mechanism.

Experimental Investigations on Impact Toughness and Shear Strength of Lead Free Solder Alloy Sn–0.5Cu–3Bi–xAg

Lead is banned in alloy making citing toxicity concerns and environmental legislations. Researchers around the world were in search of new lead free solder alloys which could replace the old Sn–Pb alloy. Solder alloys are important electronic material used in electronics package industries. In this study, shear strength and impact toughness tests were conducted on Sn–0.5Cu–3Bi when different amounts of Ag (0.25, 0.5, 0.75, 1 wt%) is added. Shear strength test is done using micro force test system. Impact toughness test is done using Charpy impact test set up by finding the energy difference before and after impact. Ultimate shear stress is found to be increased from 17.3 to 23 MPa. Yield strength is found to be increased from 23.4 to 28 MPa. Impact toughness of the alloys increased from 10.4 to 11.3 J. EDAX analysis and mapping of the Sn–0.5Cu–3Bi–1Ag is also obtained Sn–0.5Cu–3Bi–1Ag is found to be having good improved shear strength and impact toughness than Sn–0.5Cu–3Bi.

Unpaved test sections reinforced with geotextile and geogrid

Geotextile and geogrid are used routinely to reinforce the unpaved roads to enhance the serviceability and stability of these roads. Field performance studies were conducted on unpaved test sections reinforced with geotextile and geogrid to demonstrate how geosynthetics improve the test section performance using dynamic cone penetrometer (DCP). The influence of geosynthetic reinforcement was investigated by placing the reinforcement layer at subgrade-base interface, thus helps to achieve more sustainable unpaved test section. Direct shear tests were conducted on soil samples reinforced with geotextile and geogrid to investigate the improvement in shear strength of geosynthetic reinforced soil. The results of DCP test were demonstrated as dynamic cone penetration index value (DCPI, mm/blow). DCPI values were observed in range from 1 to 7 mm/blow, corresponding to 500 mm depth of penetration for unreinforced and geogrid-reinforced test section and 312 mm depth of penetration for geotextile-reinforced test section respectively. A decrease in DCPI value was observed for the geosynthetic-reinforced unpaved test section as compared to the unreinforced unpaved test section. Direct shear test results shows a significant improvement in the shear strength of soil samples reinforced with geotextile.

The shear strength of soft clay reinforced with single and group crushed brick column

Soft Clay is often known to be a problematic soils in construction because of its low strength and high compressibility characteristic. Before construction begins, ground improvement needs to be done to improve the soil bearing capacity so that the superstructure can be placed on top of it and reduce settlement and consolidation. In this study, the soft clay is going to be reinforced with crushed brick column which is part of construction waste produced during construction stage to achieve sustainable construction. This study was aimed to investigate the effectiveness of single and group crushed brick column in improving the shear strength by using laboratory scale model. Kaolin is being used as soil sample while crushed brick as the reinforced column. Few laboratory tests are conducted to determine the properties of kaolin clay and crushed brick. Unconfined Compression Test (UCT) also used to test the shear strength of the reinforced kaolin samples The improvement of shear strength of single crushed brick column with area replacement ratio of 4.00% (10mm column diameter) are 3.34%, 4.60% and 1.07% at sample penetration ratio, Hc/Hs of 0.6, 0.8 and 1.0 respectively while for area replacement of 10.24% (16 mm column diameter) are 7.56%, %, 16.37% and 4.97% at the same penetration ratio.. The result shows that the improvement shear strength for height penetration ratio of 1.0 is 13.33% which was the highest, while 0.6 and 0.8 are 12.31% and 9.79% respectively for group crushed brick columns with diameter 10mm. The improvement of shear strength is highest for height penetration ratio of 1.0 with 16.10% improvement which was slightly higher than 0.6 and 0.8 which were 13.49% and 11.35% respectively in sample reinforced with grouped columns with diameter 16mm. It can be concluded that the shear strength of soft clay could be improved by installation of single and group crushed brick column.

Interface improvement of carbon fiber/PMMA resin composites by fiber surface coating

The surface of the carbon fiber (CF) has been pretreated by liquid phase deposition of microcrystalline cellulose (MCC).X-ray photoelectron spectroscopy, atomic force microscopy (AFM) and scanning electron microscopy (SEM) have beenused to analyze and characterize the surface morphology and structure of carbon fiber, and the shear strength test and SEMobservation of single fiber interface have been performed. The interfacial adhesion properties of carbon fiber compositeshave been investigated. The results have shown that the pretreated carbon fiber deposition increases the shear strength of thesingle fiber interface by 259.3%. The analysis results have shown that the improvement of interfacial shear strength has beenrelated to the mechanical riveting between the fibers/resin and the force of the interface. Pretreatment has increased thecarboxyl groups on the surface of carbon fibers and forms hydrogen bonds between carboxyl groups, thereby improving theinterfacial properties of carbon fiber composites.

Stabilization of colluvial soil using rice husk ash and micro silica powder

Landslide is one of the major hazards in hilly regions especially when we talk about Indian Himalayan mountain ranges. Colluvial soil obtained at base of hill slope is generally week and unconsolidated which need improvement to reuse. Here work is done to improve shear strength of weak Colluvial soil of Kotropi landslide, Himachal Pradesh. This colluvial soil can be used again in various engineering work after adding certain material in it. Although various additives are available but rice husk ash and micro silica powder is selected for partial replacement of soil due to its economic, social and environmental benefits. Soil tests are conducted to get different Geotechnical properties of soil. Various samples of soil are made by adding different percentage of additives. Shear strength of different sample is compared to find optimum proportion of additives. It is observed that 15% of rice husk ash and 4% of micro silica powder provide maximum strength.

Shear strength evaluation of composite pavement with geotextile as reinforcement at the interface

This research was conducted to investigate the shear strength at the interface between polymer concrete and asphalt concrete with geotextile as reinforcement at the interface of these two types of concrete. The samples were tested for the parameters of different surface conditions [rough and smooth], curing types [room and thermal curing], temperature effect and the impact of geotextile as reinforcement. To investigate the correlation between these parameters, four different testing conditions were implemented. The results showed a significant improvement of shear strength for rough surface sample as compared to smooth surface sample. Moreover, samples cured in oven had lower shear strength as compared to samples cured in room condition. Besides that, high temperature has an adverse impact on the shear strength at the interface between polymer concrete and asphalt concrete due to the weakening of asphalt concrete at high temperature. As for samples reinforced with geotextile, the shear strength resistance was better as compared to unreinforced samples. Through visual observation, the types of failure under all testing conditions were mixed failure mode.

High-performance epoxy-based adhesives modified with functionalized graphene nanoplatelets and triblock copolymers

In this study, a high-performance epoxy-based adhesive was developed by adding graphene nanoplatelets (GNPs) and phase-separated triblock copolymers (BCPs) to enhance the lap shear strength of the adhesive joints. The GNPs were functionalized using an ultrasonicated ozonolysis (USO) method so as to achieve a homogeneous and stable dispersion in the epoxy matrix. The USO treated GNPs (OZ-GNPs) were incorporated into epoxy resin at different weight fractions using a 3-roll mill technique. Both poly(methyl methacrylate)-poly(butyl acrylate)-poly(methyl methacrylate) (MAM) and poly(styrene)-poly(butadiene)-poly(methyl methacrylate) (SBM) BCPs were mixed separately as toughening agents. Single lap shear joints were prepared by bonding aluminium sheets using the developed adhesives to study the lap shear strength of the joints. A significant improvement in the lap shear strength was observed for the hybrid epoxy system with GNPs and BCP. Adding 1.0 wt% OZ-GNPs into 10 wt% SBM modified epoxy adhesive resulted in the lap shear strength increase by 129%, compared to that of the unmodified epoxy. Raman spectroscopy and scanning electron microscope (SEM) studies found that the USO treatment facilitated the stable dispersions and improved epoxy bonding due to the oxygen functional groups introduced onto the GNP surfaces. Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and thermogravimetric analyzer (TGA) studies showed that the GNPs and BCPs were well bonded with epoxy resin without compromising the thermal stability. To better understand the influence of GNPs and BCPs on the lap shear strength, the fracture surfaces of the joints were studied using SEM. The fracture images showed that the BCPs formed different nanostructures in the epoxy matrix and the resulting nanostructures activated different toughening mechanisms that were responsible for the improvement in the lap shear strength, while the OZ-GNPs increased the joint strength by stiffening the matrix.

Investigating challenges of in situ delivery of microbial-induced calcium carbonate precipitation (MICP) in fine-grain sands and silty sand

Microbial-induced calcium carbonate precipitation (MICP) is a sustainable soil improvement method with the potential for improving the engineering properties of sand and silty soils and therefore their resistance to liquefaction-inducing events. Work presented herein experimentally investigates the changes in hydraulic conductivity of fine sands and silty sands as a result of MICP treatment. In addition, numerical modeling is conducted to assess the changes in allowable injection rate and radius of influence for the delivery of the MICP process at the field scale. The hydraulic conductivity of Nevada sand and silty sand with 15% fines content decreased through MICP application with the trend of reduction being similar for both soils. Numerical modeling results show that with the progress of the MICP process, injection rates can be increased for Nevada sand, but remain unchanged for Nevada sand with 15% silt content (after MICP treatment up to a shear wave velocity about 400 m/s.) The presence of fines by itself leads to generation of higher levels of pore-water pressure during the injection process, which necessitates higher strength improvement to prevent development of excessive plastic strains. Therefore, improvement in shear strength and stiffness relative to the magnitude of the hydraulic conductivity level and its rate of change during the MICP process is a key parameter in determining the radius of treatment.

Experimental Investigations on Impact Toughness and Shear Strength of Novel Lead Free Solder Alloy Sn-1Cu-1Ni-XAg

Abstract Lead is known to be banned in alloy making, highlighting toxicity concerns and environmental legislations. Researchers and scholars around the globe were in immediate search of new lead free solder alloys which could potentially replace the old Sn-Pb alloy. In this comprehensive study, shear strength and impact toughness tests were conducted on Sn-1Cu-1Ni when different amounts of Ag (0.25, 0.5, 0.75 1 % by wt.) is added. Shear strength test is tested using micro force test system. Impact toughness test is analyzed using Charpy impact test set up by calculating the energy difference before and after impact. The study reveals that, Ultimate shear stress increased from 19 MPa to 21.3 MPa. Yield strength increased from 27.4 MPa to 29.7 Mpa. Impact toughness of the alloys increased from 9.4 J to 10.1 J. Thus, Sn-1Cu-1Ni-1Ag is found to have improved shear strength and impact toughness than Sn-1Cu-1Ni.

Behaviour of the Undrained Shear Strength of Soft Clay Reinforced with Natural Fibre

The term soil reinforcement is conventional since decades ago for the stabilization of soft ground such as of clay and peat. Numerous research has arisen in the utilization of natural fibres as the reinforcement materials. Cost reduction, increment of sustainability awareness and eco-friendly environment are some of the advantages when using natural fibres to stabilize soft ground. A research study was carried out to evaluate the strength of the soft soil when unreinforced and reinforced using natural fibres. The findings on the experimental investigation of the study will be presented in this paper. Crushed coir fibres were used to reinforce an intermediate plasticity soft clay where both materials were collected locally in Brunei Darussalam. The crushed coir fibres were added at 0.5%, 1.0%, 1.5% and 2.0% to the dry weight of the sample. A series of an unconsolidated undrained Tri-axial test was conducted on the unreinforced and reinforced samples where the behaviour of the samples were observed and compared. The results indicated that inclusion of fibres affects the soil’s undrained shear strength. It was observed that increasing the percentage inclusion increases the undrained shear strength of the soil, up to a certain amount. Further increment of fibres, however, does not show further improvement in the undrained shear strength.