Higher Shear Strength Research Articles

Strategies for solder joints with high shear strength, slow interfacial consumption, ductile intermetallic compounds using hybrid crystalline-amorphous Co-P coatings

Crystalline and amorphous cobalt-phosphorus (Co-P) coatings have their own advantages in interfacial diffusion resistance and mechanical ductility of solder joints, respectively, but it cannot be better at both. In this work, the hybrid crystalline-amorphous Co-P coating (Co-9.1 at.% P) was fabricated and applied on the Cu/Sn interface by controlling the crystallinity through compositional design. Combining the advantages of crystalline and amorphous Co-P, strategies for solder joints with high shear strength, ductile intermetallic compounds (IMCs) and slow interface consumption was proposed. The evolution, microstructure, phase, and mechanical properties of the Co-Sn, Co-Sn-P and P-rich layers in solid-state diffusion were systematically characterized and tested by means of SEM, EPMA, EBSD, TEM, nanoindentation, and shear test. It was found that the hybrid Co-P coating achieved a low consumption rate, 14.2 nm/h, attributing to the partially crystalline structure and the Co-Sn-P exfoliation behavior. In addition, solder joints containing large-thickness ductile Co-Sn IMCs, 3.2–3.6 GPa of hardness, was established. The shear strength after aging reached 75.4 MPa relying on the large thickness of Co-Sn IMCs. Severe mechanical loads would be able to be withstand by virtue of the plastic deformation of ductile IMCs. Hybrid crystalline-amorphous Co-P would be a promising interface material in microelectronic packaging.

Surface treatment of micron silver flakes with coupling agents for high-performance electrically conductive adhesives

Coupling agents are widely used in order to improve the properties of electrically conductive adhesives (ECAs). The effects of different coupling agents on the characteristics of epoxy-based ECAs were investigated in terms of thermal, rheological, electrical and mechanical properties. Results showed that the ECAs had favourable flow, adhesion and good conductivity. In particular, the ECAs filled with Ag flakes treated with the silane coupling agent 3-aminpropyltriethoxysilane (KH-550) exhibited the lowest electrical resistivity (5.22 × 10−4 Ω cm) and the highest shear strength (20.32 MPa) among the ECAs. Besides, it had the minimum viscosity 154 Pa s at 5 rpm/25 °C. It was also found that the adding of coupling agents had different effects on the aging electrical and shear strength of the ECAs. According to this study, the use of KH-550 had a significant electrical conductivity improvement and shear strength increase before and after aging. In addition, a strong adhesion/bonding between the conductive fillers and the resin matrix was revealed by scanning electron microscopy studies.

Accelerating the Curing of Hybrid Poly(Hydroxy Urethane)-Epoxy Adhesives by the Thiol-Epoxy Chemistry.

The polyaddition between dicyclic carbonates and diamines leading to poly(hydroxy urethane)s (PHUs) has emerged as the preferred method for the synthesis of green, non-isocyanate polyurethanes. However, when proposed for use as structural adhesives, the long times for completion of aminolysis of the 5-membered cyclic carbonates under ambient conditions force the use of complementary chemistries to accelerate the curing process. In this work, a system that combines an amino-terminated PHU (NH2-PHU-NH2), an epoxy resin, and a thiol compound was employed to develop high-shear strength PHU-epoxy hybrid adhesives able to cure at room temperature in short times. A NH2-PHU-NH2 prepolymer synthesized by using a sub-stoichiometric quantity of dicyclic carbonates was mixed with a bisphenol A-based epoxy resin for the preparation of the structural adhesive. While this adhesive showed good lap-shear strength and shear resistance under static load and temperature, the curing process was slow. In order to speed up the curing process, a thiol (trimethylolpropane tris(3-mercapto propionate)) was added and its impact on the curing process as well as on the adhesive properties was evaluated. The trifunctional thiol additive allowed for faster curing in the presence of the 1,1,3,3-tetramethylguanidine basic catalyst. Moreover, a combination of NH2-PHU-NH2 and the thiol as curing agents for the epoxy resin resulted in adhesives with superior toughness, without any deterioration of the ultimate lap-shear strength or shear resistance under load and temperature, making these adhesives suitable for high-demand applications in the automotive industry.

Jet cooking dramatically improves the wet strength of soy adhesives

AbstractThe impact of jet cooking on shear strength of soy‐and‐water adhesives was investigated to understand the higher shear strength of commercial soy protein isolates compared to soy flours. Soy flour‐based wood adhesives are appealing because of their bio‐based content, low formaldehyde emission, and low cost, but their commercial application is limited by low wet cohesive strength. Previous researchers proposed that the process of jet cooking (steam injection with high turbulence followed by rapid cooling) was responsible for the high (~3 MPa) wet shear strength of adhesives made with commercially produced soy protein isolate, using the ASTM D 7998 test. In this work, we show that jet cooking did dramatically increase the wet strength of laboratory‐produced, native‐state soy protein isolate from 0.6 to 3 MPa, a strength similar to many commercial isolates. Jet cooking was far less effective at developing wet strength of soy flours, but greatly increased the viscosity of virtually all our soy materials. We hypothesize that the benefits of jet cooking are primarily a result of nonequilibrium protein aggregation states because subsequent wet autoclaving of jet cooked soy proteins dramatically decreased wet strength. The dramatic differences in adhesive properties between commercial soy protein isolates and soy flours suggests that the common practice of using results obtained with commercial isolates to predict the performance of soy flour adhesives is inappropriate.

Interface reliability and diffusion barrier property of Co-W barrier layer with modulated structure

Co-W alloy is a promising alternative of barrier layer in Sn/Cu joints in microelectronic packaging due to its appealing resistance to electro-migration and thermal fatigue. The amorphous Co-W alloy with high W content has well-performed barrier property. However, the modest interfacial strength between the amorphous Co-W and Sn limits its application. In this work, the Co-5 at. % W/Co-20 at. % W modulated-structure multilayer barriers were prepared by pulse electrodeposition with periodic change of deposition current density. The modulated Co-W barrier exhibited better diffusion barrier property with low rates of IMC growth and barrier consumption and ∼17 % higher shear strength than those of single-layer barrier. Early participation of amorphous structure slowed down the IMCs reaction during the isothermal aging in modulated Co-W barrier with 8–32 layers, while the finer grain in modulated Co-W barrier with 64–128 layers lead to quick diffusion of Co atoms, which was detrimental to barrier performance.

Parametric Investigation into the Shear Strength of Adhesively Bonded Single-Lap Joints.

In this paper, the shear strength of adhesively bonded single-lap joints were experimentally and numerically investigated. Based on the validated simulation, the effects of lap length, adhesive layer thickness, adhesive layer shape, adhesive layer overflow length, and laminate lay-up on the shear strength of adhesively bonded single-lap joints were studied. The load-displacement curves and shear strength under different parameters were compared. It was shown that the shear strength of single-lap joints gradually decreases with the increase of lap length and adhesive layer thickness, which were 53.83% and 16.15%, respectively. Considering the potential condition in fabrication, the adhesive layer shape and adhesive layer overflow length were also investigated. The adhesive with normal and triangle shape owned the comparable shear strength, which was higher than the arc one. The shear strength increased by 19.37% from 18.43 MPa to 22.00 MPa with increasing the adhesive layer overflow length to 50% of lap length. It was beneficial for shear strength to increase the adhesive layer overflow length to 50% of lap length. Among the selected four lay-ups, [0]16s had the highest shear strength, which was nearly 3 times greater than the one of [90]16s. In the real process preparation, increasing the number of 0° layers, selecting the appropriate lap length and thickness of the adhesive layer, and controlling the shape and length of the adhesive layer overflow are of great help to improve the tensile shear strength of the single-lap glue joint.

Physical, Chemical, and Mechanical Properties of Six Bamboo from Sumatera Island Indonesia and Its Potential Applications for Composite Materials.

The suitability of bamboo's basic characteristics is very important for more specific purposes, such as composite raw materials. Anatomical, physical, mechanical, and chemical characteristics are some of bamboo's fundamental characteristics. This study analyses the basic properties, such as physical, mechanical, and chemical properties of bamboo from the Forest Area with Special Purpose (FASP) Pondok Buluh Sumatera Island, Indonesia (I); analyses the relationship between the properties of each type of bamboo (II); and chooses the type of bamboo with the best properties that have the potential to be applied to composite materials, such as laminated bamboo (III). This study used materials consisting of six species of bamboo from the FASP Pondok Buluh. The manufacture of physical and mechanical test samples refers to the ISO 22157 standard, 2004, while the chemical properties test refers to the TAPPI 1999 standard. The chemical, physical, and mechanical properties of bamboo vary widely among species. The lowest holocellulose and α-cellulose content were found in the Kuning Bamboo (B. vulgaris var. vittata). The content of holocellulose and α-cellulose causes the lowest density in Kuning Bamboo (B. vulgaris var. vittata). The Dasar Bamboo (Bambusa vulgaris) has the highest levels of lignin. The substances have an impact on moisture content, T/R ratio, and shear strength. The Dasar Bamboo (Bambusa vulgaris) has the lowest moisture content, the highest T/R ratio, and the highest shear strength. However, Betung Bamboo (Dendrocalamus asper) has the highest density in this study. The compressive strength of the Betung Bamboo (Dendrocalamus asper) has the highest value. Therefore, Betung bamboo and Dasar Bamboo in this study were potentially utilized for composite materials, such as laminated bamboo.

In situ consolidation of carbon fiber PAEK via laser-assisted automated fiber placement

Automated fiber placement (AFP) of thermosetting composites has been one of the leading manufacturing techniques for aerospace structures over the last decade. Thermoplastic composites (TPCs) offer several advantages including a high toughness, recyclability, weldability, and potential for rapid out-of-autoclave manufacturing. High-power heating sources and flexible compaction rollers can be used to melt and consolidate TPC tapes via AFP to form large structures in a layer-by-layer manner as used in additive manufacturing. This paper investigates the in-situ consolidation AFP of TPC tapes (ICAT) toward their process optimization and revealing mechanisms that govern the ICAT process. To this end, a laser-assisted AFP system was utilized to fabricate short beam strength samples from carbon fiber reinforced low-melt polyaryletherketone (LM-PAEK™) at various processing parameters. Analysis of results revealed how ICAT process parameters affect interlaminar bonding, crystallinity, and void content in manufactured parts. Multiphysics finite element analysis (FEA) was also carried out to reveal mechanisms that control void, crystallinity, and bonding in ICAT. Finally, a comparison of post-fracture specimens made via ICAT with traditional compression molding was used to explain the underlying failure mechanisms in ICAT coupons. This study shows that at AFP rates of up to 0.15 m/s, high interlaminar shear strengths, up to 60 MPa, are possible to achieve with low void content (<1%) and high crystallinity (>20%), proving that ICAT is potentially a viable process for manufacturing the next generation of aerospace composites.

Numerical Study on Multiple Parameters of Sinkage Simulation between the Track Plate of the Deep-Sea Mining Vehicle and the Seafloor Soil

The seafloor soil is characterized by high water content, strong compressibility, and low shear strength. Deep-sea mining vehicles (DSMV) are prone to sinking when walking on the surface of the soil, which will cause significant reduction in traction performance. Therefore, it is necessary to study the sinkage performance. The track is usually considered the travelling mechanism of the DSMV, and the track plate is an important part of the movement system. The study of the interaction between the track plate and the soil is of great significance to the study of the DSMV’s sinkage performance. In this study, firstly, based on the in situ seafloor soil samples of 1000 m in a region of the South China Sea collected by a box sampler, the physical and mechanical parameters of soil were measured by indoor geotechnical instruments. Secondly, an elastoplastic soil numerical model similar to that of in situ soil was established. Based on coupled Eulerian-Lagrangian (CEL) method, a numerical model of the interaction between the track plate and soil was established. Considering the dynamic process, the structure of the track plate and the physical and mechanical properties of the soil, the numerical simulation were carried out under different conditions, such as different dynamic loading, the plate structural parameters and the soil physical and mechanical properties. It is found that the plate-sinkage curve were significantly influenced by these factors. The findings are as follows, firstly, with the increase in the pressure loading rate, the soil sinkage decreasing at the same pressure. On the other hand, with the increase in velocity, soil flow was accelerated, and the nonlinear relationship between resistance and velocity became more obvious; the L/B ratio of different track plates affects the variation law of the curve, and the maximum sinkage gradually decreases as the ratio of L/B increases; with the increase in the grouser height, the maximum sinkage gradually decreases, and the pressure-sinkage curve changes obviously with the grouser type; and different soil physical and mechanical properties affect the variation of pressure-sinkage curve. Innovatively, the heterogeneous soil stress distribution mode was obtained through the fitting function and Python secondary development. This study can provide a reference for studying the sinkage performance of the DSMV.

Study on layer formation behavior of Ag joints sintered with pressureless sintering process

This study focuses on investigating the relationship between sintering performance and bond layer thickness for the hybrid Ag paste consisting of micrometer-sized Ag particles and sub-micrometer Ag spherical particles. The surface morphology showed that the sub-micrometer Ag particles would contribute to improving the densification and bonding strength of the sintered Ag joint. The x-ray results indicated that the bonding quality was achieved when the bonding layer thickness was 50 μm, whereas a thinner or thicker bonding layer would lead to cracks or voids. Moreover, the microstructure of sintered Ag joints with different bonding layer thicknesses was found to be in good agreement with the results of x-ray by SEM observations. There are many cracks in the sintering structure due to the insufficient Ag paste when the bonding layer thickness is below 50 μm, while more voids appeared in sintered Ag joints when the thickness reached 120 μm, which was caused by the organic solvent volatilization. In addition, the poor densifications lead to low strengths of 7.6 MPa and 23.42 MPa for 15 μm and 30 μm thickness, respectively. The shear test results revealed that the highest shear strength was achieved on the bonding layer with a 50 μm-thick bonding layer. However, the bonding strength would decrease to 24.67 MPa and 18.64 MPa when the bonding layer thickness was 90 μm and 120 μm, respectively. The SEM observations indicated that many dimples were formed on the fracture surface with a thickness of 50 μm, which was the reason for the enhancement of bonding strength in the sintered Ag joint.

Improving the delamination resistance of oxide/oxide composites using three-dimension fiber preform

In this work, a new Slurry Infiltration and Sintering (SIS) process was proposed to fabricate three-dimensional (3D) oxide fiber perform reinforced oxide (oxide/oxide) composites. The aim of this study was to investigate the effect of slurry concentration (20–45 vol%) on mechanical properties of the 3D oxide/oxide composites. Results indicated that the SIS process had high infiltration efficient, leading to the porous matrix distributed evenly in the composite. With the increase of slurry concentration, the interlaminar shear strength increased, while the fracture toughness and work of fracture decreased. A good balance between delamination resistance and damage tolerance was achieved on the 40 vol% slurry fabricated 3D oxide/oxide composite, which had a high flexural strength of ∼332.4 MPa, a high interlaminar shear strength of ∼25.2 MPa, and a high fracture toughness of ∼11.5 MPa m1/2.

High shear strength welding of soda lime glass to stainless steel using an infrared nanosecond fiber laser assisted by surface tension

High shear strength laser welding of glass-to-metal connections are significant in various areas. However, ultrafast laser processing methods are high cost and demanding, while nanosecond laser processing requires clampers to make samples in optical contact. This work proposed an efficient approach based on liquid surface tension in ns-laser welding. Steel and glass were stably bonded together by the surface tension of the interstitial fluid and kept within optical contact (<200 nm). The two materials were welded successfully using a nanosecond fiber laser and the maximum shear strength of 9.74 MPa with a relative standard deviation of 5.3% was obtained. Meanwhile, the welding mechanism was discussed. Furthermore, a pre-welding method, expanding the available parameters range in nanosecond laser welding, was also investigated to stabilize the optical contact condition for a long time. This work provides a convenient approach for improving efficiency and reliability in laser welding industry.

Microstructure and damping property of Mn-Cu damping alloy by induction brazing and different heat treating

Mn-Cu damping alloy using in complex structural applications often experiences different thermal cycles, so the changes in the microstructure and damping properties of Mn-Cu damping alloys become a focus of attention. In this study, high frequency induction heating technique was used to prepare three-layer Mn-Cu damping structure. The microstructure and damping properties of the composite structure under different heat treatment processes and different heat treatment sequences were analyzed. The experimental results show that the composite Mn-Cu damping structure has good bonding interface and higher shear strength. After solid solution + brazing + aging, the Mn-Cu damping alloy has excellent damping properties for the formation of fine twins and about 10 μm brazing layer. In addition, with the increase of aging temperature and aging time, the quantity of twins becomes less, and α-Mn forms, which leads to the decrease of damping property. The interface between diffusion layer and brazing layer contributes to the improvement of damping properties. The specimen has the best damping property and thermal stability with the process of 900 ℃ × 1 h solid solution + brazing + 435 ℃ × 8 h aging treatment.

Experimental Investigation of Exterior Reinforced Concrete Beam-Column Connections Subjected to Reversal Loading

Eight full-scale reinforced concrete beam-column subassemblages, 4 for each non-ductile and ductile detail, were tested under quasi-static cyclic loading. All test specimens were mainly designed for gravity service loads. Four specimens named as non-ductile connections were constructed with typical reinforcement details using in Thailand. The others were assembled with details described by the seismic design building code of Thailand, known as the 1301/1302-61 code. Their performance was examined in terms of lateral load resistance, ductility index, stiffness, energy dissipation, failure modes, including joint shear strength. The test results indicated that the specimens with ductile details achieved better seismic performance in every aspect, particularly specimens with adequate joint shear strength designed according to the SST method. The ductile details have no effect to retard the stiffness degradation in the elastic range, but helped to slow the rates of stiffness degradation after the specimens reached their peak loads. The transverse reinforcement in the joints was more efficient to enhance the ductility of joints with lower joint shear strengths (J1 and J2) than the sufficient joints (J3 and J4). Based on the SST method, the connections with low shear strength capacity, J1, J1D, J2, J2D, J3, and J4 suffered with severe joint shear failure (JS), although their beam sections reached the flexural moments. On the other hand, specimens with high joint shear strengths, J3D and J4D, experienced the beam failure (BF) with mild joint shear failure (JS). Test data also demonstrated that a specimen with lesser amount of joint reinforcement exhibited satisfactory seismic behavior, as long as the joint was provided with the adequate shear strength designed by the SST method. Finally, the ACI 318 Building Code overestimated the shear strength of exterior beam-column joints. Moreover, the simplified SST model much better predicted the demand joint shear strength than the ACI 318 Code.&#x0D; HIGHLIGHTS&#x0D; &#x0D; Numerous surveys of RC buildings after earthquakes also confirmed the inadequate detailing of beam-column joints such as presence of splices, lack of hoops, deficiency of beam bar anchorage, and no steel joint stirrups in the joint&#x0D; The ductile details have no effect to retard the stiffness degradation in the elastic range, but helped to slow the rates of stiffness degradation after the specimens reached their peak loads. The transverse reinforcement in the joints was more efficient to enhance the ductility of joints with lower joint shear strengths (J1 and J2) than the sufficient joints (J3 and J4)&#x0D; The ACI 318 Building Code overestimated the shear strength of exterior beam-column joints. Moreover, the simplified SST model much better predicted the demand joint shear strength than the ACI 318 Code&#x0D; Based on the SST method, the beam-column connections with low shear strength capacity, J1, J1D, J2, J2D, J3 and J4 suffered with severe joint shear failure (JS), although their beam sections reached the flexural moments. On the other hand, specimens with high joint shear strengths, J3D and J4D, experienced the beam failure (BF) with mild joint shear failure (JS)&#x0D; The deterioration of beam-column joints under seismic could be effectively restrained by the ductile details according to 1301/1302-61 code with adequate shear strength capacity determined by using the equation of SST model&#x0D; &#x0D; GRAPHICAL ABSTRACT

Hardening of the plasma spraying coating dispersed additional phase of titanium carbide

Today in Russia, one of the most important stages in the development of additive gas-thermal technologies is the optimal choice of materials. In particular, in the field of gas-thermal methods for applying composite coatings on the surface of machine parts, plasma spraying technology is advanced and promising from the point of view of economic benefits and import substitution. In this paper, the issue of obtaining a composite coating with an additional dispersed phase (titanium carbide) is considered. The results of theoretical and practical studies on the peculiarities of hardening of the composite coating under study are presented. Calculations of shear stress according to the theories of Fischer-Hart-Pry and Orovan are presented. According to the current GOST, the shear strength of the coating under study is determined. As a result of the work, the structure of the composite coating from the sprayed material 76.5% PR-NX17CP4+23.5% TiC was investigated, namely: the structure of the sprayed composite coating in optical and scanning electron microscopy is presented. The transverse section of the composite coating is also analyzed, and conclusions are drawn on the nature of its formation. Defects of the applied layer of composite coating in the form of cracks, local delaminations, large pores were not detected. The microplate is characterized by high density, uniformity of structure, low porosity, absence of cracks and high adhesion strength of the coating to the substrate. Recommendations have been made on the possible use of plasma spraying material (76.5% PR-NH17CR4+23.5% TiC), in particular when restoring worn surfaces of aircraft landing gear racks and steering gear drives of military and civil aviation. These recommendations are justified due to the high shear strength values of the composite coating under study.

Geotechnical Evaluation of Crushed Sandstone Waste Materials from Amasiri Quarries, Southeastern Nigeria for Use in Civil Engineering Projects

This paper presents the study of crushed sandstones wastes (CSW) aiming at their utilization as main materials for the base layer of flexible pavements with series of geotechnical laboratory tests contained in American Society for Testing and Materials adopted for their evaluations. The tests conducted included particle size distribution, Atterberg limits, compaction characteristics, California bearing ratio, unconsolidated undrained compressive strength, free swell index and one-dimensional consolidation tests. Statistical analyses using proprietary computer software were used to investigate the spatial variations of the geotechnical data, and degrees of relationships that exist among the tested parameters. From the results, the Atterberg limits tests revealed intermediate plasticity with less than 35% fines (percentage passing No. 200 British Standard sieve) in majority of the samples; an indication of good highway materials. The relatively high maximum dry density, low optimum moisture content and high shear strength recorded by the tested CSW materials proved their usability in most road projects such as sub-base and subgrade. The strength indicators adopted to evaluate the validity of the CSW as pavement materials showed relatively high shear strength as the undrained cohesion values satisfy the requirement of greater than 103 kN/m2 values specified for base course materials. The empirical correlations analyses verified the influence of moisture on the strength parameters and gave a general overview of the geotechnical behaviors of the examined quarry wastes. Therefore, CSW materials are adjudge suitable but in order to achieve long term strength gain and stability especially in high volume applications, stabilizations will be required.

COMPARISON OF SHEAR STRENGTH CEMENTATION OF PREHEATED RESIN COMPOSITE AND RESIN CEMENT ON INDIRECT LITHIUM DISILICATE

Background: The success of fixed dentures is influenced by the cementation procedure. Resin cement is the most commonly used luting materials. In addition to resin cement, there are other types of luting materials, preheated resin composite. Preheating resin composite allow the material to have a low level of viscosity, therefore can be used as luting material. The purpose of this study was to evaluate the comparison of the shear strength cementation of preheated resin composite and resin cement on indirect lithium disilicate. Method: This study is experimental laboratory with post test only control group design. The sample in this study are 12 pieces lithium disilicate with diameter 5.5 mm x 3 mm cemented divided into three groups based on types of luting materials (preheated resin composite microhybrid, preheated nanohybrid, and resin cement). After the cementation procedure, the samples were immersed in artificial saliva at 37ºC for 24 hours. The shear strength test was carried out with a universal testing machine. Data analysis with using One Way ANOVA. Result: The results of the average shear strength of each group were 11.98 MPa for preheated microhybrid, 11.41 MPa for preheated nanohybrid, and 14.22 MPa for resin cement. The results of the One Way ANOVA test showed that there was a significant differences between groups (p value 0.000). Conclusion: There was a significant difference in shear strength between preheated microhybrid, preheated nanohybrid, and resin cement. The highest shear strength was the resin cement group.

Effects of the presence or absence and the position of glued edge joints in the lamina on the shear strength of glued laminated timber

Four kinds of glued laminated timber were produced (i.e., one with a glued edge-joint and the other three with nonglued edge joints) in the lamina at different positions toward the depth direction. Shear tests using an asymmetric four-point bending method were then conducted for these glued laminated timber specimens. The results showed that although the glued edge-joint specimens had the highest shear strength in all groups, the shear strength decreased as the distance from the adjacent nonglued edge-joint plane decreased. Furthermore, the shear strength of all specimens exceeded the standard shear design strength value (2.1 N/mm2) set by the Ministry of Land, Infrastructure, Transport and Tourism, Japan. Next, the shear strength of the nonglued edge-joint specimens was estimated based on that of the glued edge-joint specimens. Although the mean-estimated shear strength was lower than the mean-measured shear strength, the possibility of the shear strength changing based on the position of the nonglued edge-joint plane specimens from that of the glued edge-joint specimens was still estimated.

Design and experimental study of a fiber Bragg grating strain sensor with enhanced sensitivity.

A novel high-sensitivity fiber Bragg grating (FBG) strain sensor is reported, to the best of our knowledge. The sensitivity of the sensor is improved by fixing the FBG on an elastic substrate with a sensitization function. The sensitization principle of the designed sensor is introduced, and the mathematical model of the sensor is established. In the static and dynamic experiments of the sensor, the effect of adhesive between the sensor and the measured structure on the sensitivity of the FBG strain sensor is experimentally investigated. The experimental results show that the adhesive with high shear strength is beneficial to the realization of a high-sensitivity sensor. The sensor fixed with planting bar glue can achieve a sensitivity of 9.42 pm/µε, a repeatability error of 4.79%, and a hysteresis error of 3.36%, which is consistent with theoretical and simulation results. The designed high-sensitivity strain sensor has a simple structure, small size, and convenient installation, so it has a good application prospect in micro-strain monitoring.

Combined effect of surface pretreatment and nanomaterial reinforcement on the adhesion strength of aluminium joints

Nowadays, it is known that adhesive and cohesive forces should be developed in order to improve the mechanical performance of adhesive joints. In this context, while the adhesive forces are improved with surface pretreatments applied to the adherends, the adhesive and cohesive forces are improved with the nanomaterial reinforcement to the adhesive. For this purpose, in this study, AA7075-T6 aluminium alloy adherends were combined with epoxy adhesive as a single lap joint. As a preliminary study, abrading and FPL-etching (Forest Products Laboratory) surface pretreatments were applied to aluminium alloy adherends and after two different surface pretreatments, the changing surface morphology (with optical microscope, contact angle, profilometer measurements) and shear strength were compared. With abrading and FPL-etching surface pretreatments, an increase of 40.83% and 69.63%, respectively, was determined in the shear strength compared to untreated adhesive joints. After the preliminary study, in order to increase the mechanical performance of the adhesive joints, nano sized ANP (alumina nanopowder), MWCNT (multiwalled carbon nanotubes) and SNP (silica nanopowder) were added to the adhesive. Thus, it was investigated how the combined effect of different surface pretreatments and nanomaterial types at various reinforcement ratios changed the shear strength of the adhesive joints. After shear tests, significant increase in shear strength was observed in FPL-etched adhesive joints compared to abraded adhesive joints in all reinforcement nanomaterial types and reinforcement ratios. And also, significant improvements in the shear strength of adhesive joints were determined in all types of nanomaterial reinforcements. The highest shear strength was obtained at 10.0 wt % SNP reinforcement with 104.32% improvement in FPL-etched adhesive joints compared to nonreinforced FPL-etched adhesive joints. The evaluation of shear strength was supported by the failure images taken from the fracture surfaces after shear tests, and it was determined that the failure type was changed from adhesive to cohesive with nanomaterial reinforcement compared to nonreinforced adhesive joints.