Enhancement Of Shear Strength Research Articles

Enhancement of interfacial shear strength due to cooperative π-π interaction between polyphenylene sulfide and carbon fiber and molecular orientation of polyphenylene sulfide via the π-π interaction

Enhancement of interfacial shear strength due to cooperative π-π interaction between polyphenylene sulfide and carbon fiber and molecular orientation of polyphenylene sulfide via the π-π interaction

A supersaturated Cu-Ag nanoalloy joint with ultrahigh shear strength and ultrafine nanoprecipitates for power electronic packaging

Ag-Cu bimetallic nanoalloy, integrating the advantages of reducing migration and cost of nano-Ag and alleviating oxidation of nano-Cu, is a prospective bonding material for power electronic packaging. The Ag-coated Cu nanoparticles (Cu@Ag NPs) paste can execute bonding with high quality at 250 °C, and the achieved supersaturated Ag-Cu nanoalloy joint with ultrahigh shear strength (152 MPa) dramatically exceeds most nano-paste joints. The interstitial solid solutions with atomic-level metallurgical bonds at the interface dominantly promoted the shear strength. Besides, the numerous ultrafine nanograin, high proportion of low angle grain boundaries (7.44%) without deformation, and the Cu nanoprecipitates in the joint would improve subordinately. Furthermore, the high content (16.8%) of Σ3 twin boundaries would contribute to the electrical and thermal conductivity. Thus, the multiple strengthening mechanisms with the solid solution, the second precipitated phase, and ultrafine nanograin can dramatically enhance shear strength and electro-thermal conductivity of joints for high-temperature device packaging.

Investigation of the process of pipeline penetration at a shallow embedment in clay with large-deformation analysis

Pipe-soil interaction is an essential aspect of a deep-water pipeline system. It may significantly influence both the structural behavior and integrity of the pipeline during installation and operation. The pipe embedment is an important factor influencing the pipe-soil interaction for an exposed pipeline. The embedment will determine the boundary conditions around the pipe for the subsequent loading scenarios. In this paper, based on the assumption of plane strain, the “Remeshing and Interpolation Technique with Small Strain” (RITSS) method was used to establish the large deformation finite-element model of vertical penetration of pipelines in clay. Compared with the previous literature, the robustness of the model was verified. Based on this model, the development mechanism of the soil shear band has been discussed during pipeline penetration; the effect of pipeline roughness on the undrained shear strength degradation mechanism and enhancement mechanism has been further explored. Finally, the effects of soil buoyancy, soil strength gradient, strain softening, and strain rate on the penetration resistance were discussed through parametric analysis. According to the influence sensitivity of each parameter, the evaluation framework of the penetration resistance has been developed. Compared with the previous literature, the validity of the framework was verified. The framework could provide guidance and reference for designing vertical penetration of pipelines in deep-water engineering.

Shear Strengthening by GFRPU on an RC Column with Nonseismic Reinforcement Details.

Structures constructed before seismic design standards in Korea were enacted are being seismically and structurally strengthened for structural performance. The jacket method has been used to enhance the shear load-carrying capacity and ductility of reinforced concrete columns. This study investigated the effect of glass fiber-reinforced polyurea (GFRPU) on the enhancement of shear strength and ductility. It was shown that the GFRPU spraying technique played an important role in enhancing the column because of the material characteristics of the GFRPU, that is, high-tensile strength and elongation. The reinforcement effect of GFRPU on the shear-span ratio and axial-force ratio of six reinforced concrete (RC) column specimens was evaluated. The experimental results demonstrated that the lateral-reinforcement effect and energy-dissipation capacity were improved. The H-series and S-series specimens reinforced by the GFRPU with an axial-load ratio of 0.1 exhibited higher shear strength, of about 30% and 18%, than the specimens without reinforcement. The shear-load-carrying capacity of the S-series specimen with the axial-load-force ratio of 0.2 increased by 4%. The design method representing the lateral-resistance ability of the GFRPU was represented by an empirical formula reflecting the experimental results.

Surface modification of carbon fibres with ammonium cerium nitrate for interfacial shear strength enhancement

An ongoing research focus in the carbon fibre (CF) field has been to identify a practical and more effective surface modification method for improving CF's interfacial adhesion and bonding capacity, which is vital for achieving high performance CF composites. In this research, carbon fibres were modified by using a new and facile treatment process in an aqueous solution of ammonium cerium nitrate (ACN) at a low temperature (20 °C–50 °C). The surface analysis results revealed that the ACN treatment imparted a combined effect of CF surface oxidation and cerium (IV)/(III) immobilisation on the oxidised CF surface through coordination bonds, leading to a significantly increased specific surface area, surface energy and surface reactivity. These new surface characteristics directly contributed to an improved CF interfacial adhesion and load transfer between the modified CFs and an epoxy matrix. The study demonstrated that under specified conditions, the new treatment method resulted in 304% increase in interfacial shear strength (IFSS) and 130% increase in interlaminar shear strength (ILSS) without any significant reduction in CF's mechanical properties. In comparison, the ACN modification yielded CFs with a much higher ILSS than the current industrial processes using electrochemical oxidation and sizing.

A review on performance of near‐surface mounted‐carbon fiber‐reinforced polymer laminates bonded into slits

AbstractThe near‐surface mounted (NSM) technique over the years has become the most popular retrofitting technique for obtaining enhanced strength and durability in reinforced concrete structural elements. It is mostly preferred for its easy application of composites in grooves cut on specimen concrete cover. The specimen surface is prepared with slits where polymer composite laminates are placed along with adhesives as filler to attain good bonding between laminates and the surface. The paper reviews the NSM carbon fiber reinforced polymer technique and its ascendancies over externally bonded composites retrofitting approach. Members strengthened with the NSM technique show enhanced shear strength, flexural capacity, and fatigue resistance. Motivated by the urge of gaining knowledge on various advantages of this emerging method, the paper reviews the load‐carrying capacity, failure modes, durability, and bonding behavior along with the enhancement ascertained in shear, flexure, and fatigue resistance by the NSM technique. In addition to offering guidance on the experimental and computational investigations on the overall behavior of the technique, the present review also intends to encourage further development in the near‐surface mounted carbon fiber polymer strengthening system of retrofit.

Study of the geotechnical behavior of soil-cement reinforced with plastic bottle fibers

This study aimed to evaluate the influence of adding plastic bottle fibers to soil-cement mixtures and the possible improvements generated by the addition of a blend of two types of additives, namely, additive 1 (waterproofing improver) and additive 2 (adhesion enhancer), in the compactability and shear strength parameters of soil-cement-plastic fiber mixtures, considering a tropical residual soil. The fibers used in this study are made of Polyethylene Terephthalate (PET), produced from soft drink bottles, and added to the soil with 2 mm width and 1 cm length, in the content of 1% in relation to soil dry mass. Also, contents of 3% and 5% Portland cement, in relation to soil dry mass and two additives, additive 1 at a ratio of 0.25 kg m-³ dry soil and additive 2 at a ratio of 0.60 kg m-³ dry soil, were used to evaluate the possible effect of these variables on the investigated engineering behavior parameters. The compaction results indicated that the inclusion of PET fibers in soil-cement mixtures tends to decrease the maximum dry unit weight compared to fiber-free mixtures. Also, if compared to soil-cement-fiber mixtures, the incorporation of additives to soil-cement-fiber composites resulted in higher values of maximum dry unit weight and lower values of optimum moisture content, but still maintaining values lower than obtained for compacted soil. Results of the direct shear test showed enhanced shear strength with the addition of fibers to soil-cement, for both the parameter of cohesion and the internal friction angle of the material in comparison to fiber-free composites, which demonstrates the potential application of these composites in geotechnical works.

Feasibility Study of Petrochemical Waste and Cement Usage for Saline Road Subgrade Stabilisation

The widespread distributions of saline soils in Iran cause a range of problems for road construction projects due to insufficient shear strength, salt solubility potential and swelling. This paper conducts experimental tests using different cement contents and a sort of petrochemical waste with two curing methods to stabilise saline soil samples. Strength, compressibility and chemical tests were conducted, X-ray diffraction analyses were performed, and scanning electron microscope pictures were prepared for basic materials and stabilised saline soil samples in this paper. The results indicate that both petrochemical soda ash waste and cement enhance the shear strength of saline soil, especially after 28 days of curing. However, the combination is more appropriate from the swelling and salt solubility potential viewpoint. The optimum combination of 2% cement and 5% of petrochemical soda ash waste, cured by method 2 for 28 days, results in the most significant shear strength enhancement (127%). Furthermore, a swelling quantity of the optimum combination is reasonably restricted. X-ray diffraction test results and scanning electron microscope pictures demonstrated that despite the presence of ettringite agents, the formation quantity of these minerals is negligible. The salt is well stabilised, and its solubility potential dramatically decreases.

Enhanced interfacial properties of hierarchical MXene/CF composites via low content electrophoretic deposition

The weak fiber-matrix interface is a bottleneck hindering the development of carbon fiber composites . In this work, an optimized electrophoretic deposition (EPD) approach was explored to improve the interfacial properties by depositing uniformly two-dimensional MXene (Ti 3 C 2 T x ) nanoparticles onto the surface of carbon fibers (CF). The MXene-CF hybrids were then used to fabricate continuous carbon fiber reinforced polymer (CFRP) composites. The results manifested that the presence of MXene nanoparticles on the CF surfaces could significantly increase the fiber surface energy and wettability , as well as their surface roughness. As a result, a remarkable increase of the interfacial strength and flexural properties of CFRP has been observed. The functionalized MXene–CF–epoxy composites witnessed a prominent enhancement of interlaminar shear strength (ILSS), flexural strength and monofilament tensile strength compared to their unfunctionalized counterparts. The versatile EPD strategy proposed herein, constitutes a promising approach for CFRP modification that can lead to significantly improved performance. • A homogeneous MXene attachment to the CF surface was achieved via a novel EPD process. • The EPD technique was optimized to prevent oxidation and agglomeration of MXene nanoparticles. • Enhancements of 75%, 50.4%, and 32.7% in ILSS, flexural strength, and single fiber tensile strength were obtained. • The interfacial strengthening mechanism was ascribed to mechanical interlocking, local stiffening, and hydrogen bonding.

Experimental study of shear behavior of CFRP strengthened ultra-high-performance fiber-reinforced concrete deep beams

This experimental study aims to examine the effectiveness of shear stirrups and carbon fiber-reinforced polymer (CFRP) strengthening scheme in enhancing the deep beams’ shear strength. For this purpose, a total of six deep beam specimens of 150 mm × 300 mm (depth) × 1000 mm with an effective span of 750 mm, classified into three groups of two specimens each, were prepared. The beams of the first group were of normal concrete (NC). The beams of the second group were prepared using ultra-high-performance fiber-reinforced concrete (UHPFRC). In the third group, the UHPFRC deep beams were strengthened using CFRP strips. Each group had two beams – one with no shear stirrups and another with shear stirrups. All deep beams were tested under four-point loading until failure. According to the experimental results, shear stirrups effectively contributed to enhancing shear strength, ultimate load, and deformation capacity for NC deep beam. By utilizing the UHPFRC mix, the deep beams’ shear strength was upgraded significantly compared with the NC deep beams, but the deformation capacity was reduced. The implemented strengthening scheme was effective in the enhancement of deep beams’ shear strength and deformation capacity. The improvement in the shear strength of strengthened UHPFRC deep beams was moderate (16%); however, a considerable increase was observed in the deformation capacity as the displacement and energy ductility indices were enhanced by 49% and 185%, respectively.

Fast and Reliable Ag\u2013Sn Transient Liquid Phase Bonding by Combining Rapid Heating with Low-Power Ultrasound

Ag–Sn transient liquid phase (TLP) bonding is capable of producing joints with excellent mechanical and thermal properties, and with operation temperatures at or even above the processing temperature. However, reduction of the comparatively long processing times required to achieve high-quality joints is highly desirable. To this end, the use of fast heating and low-power ultrasonic (US) pulses for accelerated Ag–Sn TLP bonding is investigated with particular focus on defect generation and avoidance. Employing rapid heating with 20,{text {K s}}^{-1}, the process time can indeed be strongly reduced, yielding a high average shear strength of (58 pm 22) MPa. The large variance of the shear strength is caused by gas entrapment and pronounced lateral squeeze-out of liquid Sn, facilitated by the suppression of {text{Ag}}_{3} {text{Sn}} formation upon rapid heating. Introduction of a weak US pulse leads to enhanced {text{Ag}}_{3} {text{Sn}} formation and efficient removal of entrapped gas, and thus to avoidance of large-scale bond defects, which results in an enhanced shear strength of (104 pm 8) MPa.

Enhanced adhesive performance of Ti–6Al–4V/PEEK interface by loading SPEEK on Ti–6Al–4V plates

With the rapid development of the aerospace industry, fiber metal laminates (FMLs) have become crucial composite structures due to their desirable properties. However, FMLs still suffer from poor adhesive performances. In this work, sulfonated poly-ether-ether-ketone (SPEEK) was selected as a modifier to enhance the adhesive performance between Ti–6Al–4V alloy (TC4) plates and PEEK. Anodizing and sandblasting were also utilized as pre-treatments to explore possible synergistic effects with SPEEK modification. The treated TC4 plate surfaces were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), contact angle (CA) measurements, and scanning electron microscopy (SEM). Meanwhile, the adhesive performances were evaluated by single lap shear testing. The successful loading of SPEEK on TC4 plates led to enhancement in interlaminar shear strength by 32.11% to reach 40.77 MPa when compared to the value of the unloaded anodized sample. The surface morphologies revealed bonding mechanisms based on mechanical interlocking, molecular entanglement, hydrogen bonding formed between sulfonic and carbonyl groups, and highly enhanced van der Waals forces generated by sulfonic groups. In sum, these findings look promising for resolving issues related to Ti/PEEK laminate interfacial strengths.

Influence of glass fibre reinforced polymer composite pin reinforcement on shear and dynamic behaviour of composite joint manufactured through co-cure technique

The co-cure technique efficiently joins composite components in wings, ailerons, skins, ribs and spars in aeronautical applications. The present study investigates the effect of through-thickness reinforcement of glass fibre reinforced polymer composite pin on shear and dynamic properties of co-cured composite joints. The experimental results exhibited that through-thickness reinforcement with 2% composite pin volume significantly improved the shear strength and elongation limit by 38.4% and 102.4% compared to unpinned joints. Furthermore, composite pin reinforcement changed the catastrophic failure of co-cured joints to progressive failure due to the tougher bridging traction of composite pins. The comparison of fractured surfaces exposed that debonding, composite pin pull-out and shear fracture of pins are the major failure mechanisms involved in enhanced shear strength and progressive failure of co-cured composite joints. The experimental modal analysis avowed that through-thickness reinforcement with 2% composite pin volume improved the fundamental natural frequency of the co-cure joints, while co-cure joint reinforced with higher volume (4%) of composite pins had higher damping value due to excessive fibre damage, which increased interaction between composite adherent and adhesive.

Experimental and numerical study of interlaminar shear property and failure mechanism of none-felt needled composites

The none-felt needling technology improved the interlaminar peeling and in-plane tensile property of the needled fabric. Following the previous research, this paper proposed a study on the interlaminar shear property of the none-felt needled composites by using experiments and numerical methods, and compared with common felt/base cloth needled composites. Result showed that none-felt needled composites had great enhancement in interlaminar shear strength, increased by up to 108.6%. Double cohesive zone models were established to predict the mode Ⅱ interlaminar shear property of none-felt needled composites. The simulation of interlaminar shear strength and the surface strain cloud graph were well close to the experimental results. Moreover, tensile and bending properties were also characterized. The in-plane tensile strength and modulus increased by up to 21% and 20% respectively. The bending strength and modulus improved by 3%–7% and 4%–13%. The none-felt needling technology realized the simultaneous enhancement of interlaminar shear and in-plane tensile properties of needled composites, which may further broaden the application fields of needled composites.

Uplift resistance of buried pipelines: The contribution of seepage forces

Pipelines are commonly buried, and can buckle upwards when heated if there is insufficient soil uplift capacity. Interface tension beneath the buried pipe significantly influences the uplift capacity at shallow embedments. Conventional design approaches, which consider either zero or unlimited interface tension, do not assess and quantify the effect of interface tension on uplift capacity. The present study bridges the gap between conventional “no tension” and “full tension” capacities. Mobilisation of interface tension is governed by seepage forces which in turn directly control the formation of a gap beneath the pipe. A large deformation finite element approach, which simulates this phenomenon of gap formation using a thin layer of gap elements below the pipe, is adopted to study the soil response for various cases of uplift velocity, embedment and soil weight. The enhancement in undrained shear strength of soil at higher uplift velocities due to strain rate effects has also been considered. The interface tension mobilised at these different velocities and embedments varies systematically in a way that is expressed by modifying Hvorslev's intake factors. The proposed expressions may be used with the existing methodologies to assess pipe stability during operation, demonstrated here through a design example.

Numerical and experimental investigations on the enhancement of the tensile shear strength for resistance spot welded TWIP steel

The microstructure manipulation by adjusting the content of alloy element plays a significant role in the material fabrication, and resistance spot welded joint has a crucial effect on the stable and safe operation of the vehicles. In the present study, a special method by simultaneously inserting the interlayers of Al foils and interstitial-free steel (IFS) is proposed to directly manipulate the nugget structure and enhance the tensile shear strength (TSS) owning to the change of heat and mass transfer. The welded joint in the original state (TWIP-A) possesses the TSS of 15.2 kN on average with an interfacial fracture (IF) mode while the TSS can reach 26.5 kN for the microstructure-manipulated specimen (TWIP-B) with a button fracture (BF) mode. The existence of the Mn element segregation and austenite with the columnar structure triggered the formation of IF mode for specimen TWIP-A. After adding the Al foils and IFS, the segregation of element Mn is reduced. The high welding current and long-term duration at high temperature are beneficial for the formation of the equiaxed grain zone (EGZ) in the nugget for specimen TWIP-B. The change of the structure morphology, strengthening effect by element Al and the relief of Mn segregation in the nugget for specimen TWIP-B can hinder the crack to propagate along the centerline, causing the failure mode transition to BF. The present study clearly shows the correlation between the microstructure and TSS and the strategy can guide the optimization of the RSW schedule of high strength steels and even their manufacturing process.

Interaction of flange and web slenderness, overstrength factor and proposed stiffener arrangements for long links

This paper is aimed to investigate the interaction of flange and web slenderness ratio, overstrength factor and also to improve the behavior of long links. Pursuant to these goals, 150 numerical models of different long links were developed and exposed to cyclic loading protocol mandated by AISC 341. Link length ratio, flange and web slenderness and stiffener configurations are selected as parameters. The results revealed that the flange slenderness ratio can be relaxed to 0.38(E/Fy)0.5 for long links if the web slenderness ratio is <1.5 (E/Fy)0.5. The shear capacity of long links decreases as the link length ratio increases. The results of shear capacity showed the overstrength factor required by AISC 341 overestimates the shear capacity; therefore, two different equations to predict the overstrength factor for long links are proposed. The stiffener configuration recommended by AISC 341 limits the potential of long links. To mitigate this drawback, different stiffener configurations are proposed to empower the behavior of long links. Using additional one stiffener at each link ends can enhance shear strength, energy dissipation and plastic rotation capacities by 25%, 447% and 322%, respectively. When two additional stiffeners are introduced, these ratios modify to 29%, 479% and 332%. Moreover, rupture index values are utilized to verify proposed stiffener configurations further.

Micro-mechanism of Shear Strength and Water Stability Enhancement of Montmorillonite by Microwave Heating

Microwave heating potentially reinforces the muddy intercalation to eliminate slope failure. Montmorillonite has the worst water resistance among the muddy intercalation components, which is a primary facet of inducing muddy intercalation failure. This study investigates the mechanism of shear strength and water stability enhancement of montmorillonite heated by the microwave oven and muffle furnace from room temperature to 800 °C. Results show that montmorillonite mineralogical evolution can be divided into three stages: room temperature-300 °C, 300-600 °C, and 600-800 °C. Microwave heating is more efficient in montmorillonite heat treatment than muffle furnace heating and makes the montmorillonite dehydroxylated earlier. It is worth noting that hot spots formed inside the montmorillonite specimens during the microwave heat treatment. Microwave significantly promotes the shear resistance of montmorillonite, where the maximum increases are 39.94% of cohesion at 600 °C and 20.54% of internal friction angle at 700 °C. This enhancement is due to the rough surfaces and large particles produced by dehydroxylation and Mg-Al spinel synthesis, and the significant degree of disorder state of MMT after dehydroxylation also plays a vital role. The microwave-heated montmorillonite over 500 °C presents good integrity in the water immersion test over 24 h. Considering the shear behavior and water stability, we believe the most reasonable heating interval for microwaves is 500-600°C.

Influence of truss-type and welded reinforcement in concrete beam

In present study, the shear strength of the conventional reinforced concrete beam (here named as non-welded rectangular stirrup beam - NRSB) is compared with three types of beam having modified reinforcement patterns, named as welded rectangular stirrup beam (WRSB), non-welded Warren truss beam (NWTB) and welded Warren truss beam (WWTB). Such names are given based on the stirrup orientation. All beams have the same concrete dimension and the same total weight of reinforcement, ensuring no variation of cost. From the test results, the average shear strength enhancement of WRSB, NWTB, and WWTB was found to be more than 17%, 10%, and 30% compared with conventional NRSB. WWTB was proposed to be the best alternative. To design the above-mentioned beams, design equations are proposed and verified. Use of finite elemental software reveals that in reinforcement the stress intensity (Von-mises) is the maximum in WWTB, followed by WRSB, NWTB and finally NRSB.

Interfacial shear strength enhancement of polymeric macro-fibers via plasma treatment

This work deals with a utilization of a plasma treatment of polymeric macro-fibers used as reinforcement in the cement composites. Commercial fibers BeneSteel were plasma treated to reduce their weaknesses – smooth and chemically inert surfaces and thus to enhance an interfacial shear strength between them and the cement matrix. The low-pressure cold oxygen plasma treatment was done for both physical (roughening) and chemical (surface activation via active polar groups) surface modifications. A plasma exposition time differed between 5 and 480 seconds, while the surface changes were observed. It was shown that the most effective treatment time was equal to 30 seconds, as proven by a wettability measurement between fibers and demineralised water. To determine the interfacial shear strength between reference and chosen modified fibers, pull out tests from the cement matrix was performed. Finally, thus treated fibers were used as the reinforcement in concrete composites. Concrete samples having dimension equal to 100 × 100 × 400 mm were tested in the three-point bending test. We focused especially on the post-cracking response of tested samples. The results showed that the post-cracking residual flexural strength of samples reinforced with plasma treated fibers was higher by 30 %. It was find out that the utilization of plasma treated fibers is more effective if compared to reference ones. Copyright © 2017 VBRI Press.