Higher Shear Strength Research Articles

Dissimilar material joining of densified superwood to aluminum by adhesive bonding

Superwood is a densified wood product that shows promise as a lightweight and renewable alternative for metallic materials. In order for this high-performance new material to be used in multi-material products, it must be able to be joined with other major materials. For example, joining superwood to aluminum would provide a key enabling technology for its use in automotive components since aluminum is presently a major lightweight material for such applications. In this paper, a methacrylate-based adhesive has been identified to provide high lap shear strength (7.5 MPa) for aluminum-to-superwood joints. The aluminum-to-superwood samples were prepared with different amounts of pre-polishing to create openings to the pores in the superwood so adhesive could penetrate into them and create a mechanical interlock, in addition to the hydrogen/chemical bonding at the surface between the methyl methacrylate (MMA) in methacrylate-based adhesive and the cellulose in superwood. For aluminum samples, a thin layer (typically a few nanometers) of oxide film on the surfaces provides hydrogen/chemical bond to MMA structure in the adhesive layer. The failure strength of the superwood-to-aluminum joint sample is about 50% higher than that of natural wood to natural wood joint sample and comparable to that of aluminum-to-aluminum joint sample.

Interface enhancement and distribution of carbon fibers in injection welding

AbstractInjection welding is an excellent adhesive‐free bonding method for thermoplastic resins, demonstrating outstanding connection effectiveness. The incorporation of carbon fibers (CFs) significantly enhances the weld shear strength at the injection interface. This study aims to investigate the reinforcement effect of CF‐reinforced thermoplastic composites (CFRTP) during the injection welding process. And explore the influence of the amount of added CFs on the weld shear strength. Polyamide 6 (PA6)/CF composites with CF contents of 10 wt% and 30 wt% were subjected to injection welding for the first and second molding cycles, respectively. It was observed that the reinforcement effects varied considerably depending on the combinations studied. Under the optimal combination and process parameters, the weld shear strength of PA6/CF composites reached 63 MPa, equivalent to 90% of the shear strength (70 MPa) of the original PA6/CF material. Polarized light microscopy and scanning electron microscopy were utilized to analyze the distribution of CFs at the interface and the reinforcing mechanism during tensile fracture. The significance of maintaining uniform CF content during the welding process of PA6/CF composites was emphasized.Highlights Preparation of PA6 composite materials with different carbon fiber contents. Achieving high welding shear strength of composite materials through injection welding. Identified the optimal injection welding conditions to achieve the highest strength. The positive effect of specific fiber distribution on welding strength was analyzed.

Properties of hybrid glued-laminated timber manufactured from peeler cores

ABSTRACT The aim of the present study was to determine some basic physical and mechanical properties of a hybrid glued-laminated timber manufactured from peeler cores (GLPC) as by-products of plywood manufacturing, ensuring more complete and efficient utilisation of wood raw materials in high value-added applications. The GLPCs were manufactured from beech and poplar wood at different ratios by using several combinations of lamellae with trapezoidal cross-sections. The highest density ρmax of 572 kg.m−3 (ρmean = 544 ± 12.9 kg.m−3) was determined for the beams manufactured at beech:poplar ratio of 1:1. The modulus of rupture (MOR) and modulus of elasticity (MOE) were 71 ± 9.4 N.mm−2 and 12,809 ± 1211.7 N.mm−2, respectively. The highest shear strength were obtained for the beams manufactured by gluing beech to beech: f v , g , k ( 60 ) = 17 ± 3.8 N.mm−2. The greatest values when testing the compressive strength and tensile strength of the GLPC were found for combination beech 50%/ poplar 50%: f c , g , k ( 90 ) = 60 ± 8.6 N.mm−2 and f t ( 0 ) , g , k = 42 ± 8.0 N.mm−2. All types of beams produced in laboratory conditions met the minimum requirements of the GL 32c and GL 32 h classes.

The Impact of Vegetation Types on Soil Hydrological and Mechanical Properties in the Hilly Regions of Southern China: A Comparative Analysis

Background: Vegetation roots are considered to play an effective role in controlling soil erosion by benefiting soil hydrology and mechanical properties. However, the correlation between soil hydrology and the mechanical features associated with the variation root system under different vegetation types remains poorly understood. Methods: We conducted dye-tracer infiltration to classify water flow behavior and indoor experiments (including tests on soil bulk density, soil organic carbon, mean weight diameter, soil cohesion, root density, etc.) to interpret variation patterns in three forest systems (coniferous and broad-leaved mixed forest, CBF; coniferous forest, CF; Phyllostachys edulis, PF) and fallow land (FL). Results: Based on the soil dye-tracer infiltration results, the largest dyeing area was observed in CF (36.96%), but CF also had the lowest infiltration rate (60.3 mm·min−1). The soil under CBF had the highest shear strength, approximately 25% higher than other vegetation types. CF exhibited the highest aggregate stability, surpassing CBF by 98.55%, PF by 34.31%, and FL by 407.41%, respectively. Additionally, PF forests showed the greatest root biomass and length. The results of correlation analysis and PCA reveal complex relationships among hydrological and mechanical soil traits. Specifically, soil cohesion does not exhibit significant correlations with hydrological traits such as the dyeing area, while traits like MWD and PAD show either positive or negative associations with hydrological traits. Root traits generally exhibit positive relationships with soil mechanical traits, with limited significant correlations observed with hydrological traits. Conversely, we found that root biomass contributes significantly to the dyeing area (accounting for 51.48%). Conclusions: Our findings indicate that the reforestation system is a successful approach for conserving water and reducing erosion by increasing soil-aggregated stability and shear strength, causing water redistribution to be more homogenized across the whole soil profile.

A method for manufacturing a mechanically strong and durable hybrid structure of polyethylene–hydroxyapatite composite and titanium alloy

AbstractThe integration of polymer, metal, and ceramic materials in hybrid structures represents a potential but underexplored alternative for biomedical applications. Here, we present a methodology for manufacturing a mechanically strong and durable hybrid overlap structure from a composite of green high‐density polyethylene (HDPE) and hydroxyapatite (HA) compatibilized with HDPE‐g‐MAH joined to a substrate of Ti6Al4V alloy. This process involves laser structuring of micro‐scale grooves on the metal surface, followed by injection overmolding of the polymer composite. A hybrid overlap joint with strong interfacial anchoring was achieved, resulting in outstanding joining strength and fatigue life. This achievement holds significant promise for future biomedical applications.Highlights Joining of composite of HDPE–HA with Ti6Al4V alloy via injection overmolding Laser texturing was effective in improving mechanical interlocking A hybrid joint with high shear strength and fatigue life was developed The hybrid joint is promising for biomedical applications

Magnetorheological fluids: A comprehensive review

The magnetorheological (MR) fluids contain magnetic micro-sized iron particles, non-magnetic-based fluid, and some additives in order to mitigate sedimentation and agglomeration. The various carrier fluids used in the preparation of MR fluids are mineral oil, silicon oil, castor oil, soybean oil, kerosene, synthetic oils, honge oil, organic oil, water-based oils, etc. However, for obtaining better vibration control, silicone oil is the most preferred one due to its higher viscosity index, lower friction characteristics, higher flash point, and higher shear strength. The MR fluids have various application areas such as dampers, prosthetic knees, valves, brakes, clutches, finishing processes etc. The dampers containing MR fluids are used in automobile cushioning for enhancing passenger comfort and MR suspensions significantly improve steering stability in vehicles. In case of MR brakes, the braking torque on the rotating disks is controlled using the generated shear stress. The carbonyl iron (CI) particles exhibit better rheological characteristics as compared to electrolytic iron (EI) particles. The use of MR fluids produces stable and natural limb movement in orthoses, lower limb prostheses, and exoskeletons. The MR fluids also prove to be very significant in polishing applications. There are various issues with preparation methods and difficulties in the storage of MR fluids. The problems encountered in the synthesis of MR fluids include sedimentation, agglomeration, in-use thickening, corrosion, erosion, etc. The impact of particle proportion, particle shapes, and size has been influential in evaluating MR characteristics. The viscosity and shear stress of MR fluid have been mitigated at higher values of temperature and even CI particles get oxidized at higher temperatures. The CI particles as compared to EI particles are the majority favourable particles used for dispersing state within the MR fluids due to their higher value of saturation magnetization, more availability, and lesser cost. The small-sized particles led to lower wettability, whereas larger-sized particles accounted for an increased sedimentation rate. The currently available MR fluids cost is still on the higher side and the preparation of economical MR fluid is still a big challenge for the researchers. The MR fluids storage is also a big concern. The future scope of MR fluid may be in heavy industries such as nuclear, shipbuilding, oil and gas, space and aviation, etc. to achieve the desired damping response.

Genetic Variability of Traffic Tolerance and Surface Playability of Bermudagrass (Cynodon spp.) under Fall Simulated Traffic Stress

Bermudagrasses (Cynodon spp.) are the most preferred turfgrass species for athletic fields in the southern and transition zones of the United States. Developing and using bermudagrasses with superior traffic tolerance and surface playability under trafficked conditions benefits turfgrass managers, athletes, and sport organizations. A 2-year field study was conducted in Stillwater, OK, to quantify the genetic variability of traffic tolerance and surface playability from a population composed of two commercially available and 87 experimental interspecific hybrid bermudagrasses under fall simulated traffic stress. The experiment design was a randomized complete block design with three replications. Plots were subjected to 60 simulated cleat traffic events for 6 weeks in the fall of 2019 and 2020 using a Baldree traffic simulator. Bermudagrasses were evaluated for turfgrass quality (TQ), normalized difference vegetation index (NDVI), fall percent green cover (FPGC), shear strength (SS), and surface hardness (SH) after 3 and 6 weeks of traffic. Spring green-up percent green cover (SGPGC) was evaluated in the spring of 2020 and 2021. Except for SH, significant entry effects were found for all parameters and reliability estimates were moderate to high (i2 = 0.49 to 0.68) under simulated trafficked conditions. Experimental entries 17-4200-19X13, 17-4200-19X9, 17-4200-36X19, 17-5200-4X11, 18-7-2, 18-7-6, 18-8-2, 18-8-3, 18-8-7, 18-9-2, OSU1101, and OSU1664, and TifTuf® had excellent traffic tolerance. Entries 18-8-7, OSU1101, OSU1675, TifTuf®, and Tahoma 31® demonstrated high SS. There was a large group of entries that had consistent early spring green-up across both years, including Tilin#5, 18-9-8, OKC1221, OSU1257, OSU1318, OSU1337, OSU1406, OSU1439, OSU1651, OSU1675, Tahoma 31®, and TifTuf®. OSU1101 was the entry ranking in the top statistical grouping most often throughout the study. Findings illustrated the possibility of improving traffic tolerance and SS through breeding and using phenotypic selection could reliably select bermudagrass genotypes with improved traffic tolerance and SS in the transition zone.

Effects of secondary bonding process parameters on the bonding and mechanical properties of bamboo scrimber composite: Glue type, spread rate and pressure

Bamboo scrimber composite (BSC), which demonstrates huge potential in construction applications is a novel composite material prepared from bamboo and phenolic resin. The aim of this study was to address the issue regarding the size of BSCs via a secondary bonding mechanism. In this work, the effects of glue type, spread rate and pressure on the bonding and mechanical properties of secondary bonding-bamboo scrimber composites (S-BSCs) were investigated. The bonding properties were tested through shear and delamination tests, and the mechanical properties were characterized by modulus of rupture (MOR), modulus of elasticity (MOE) and compressive strength(CS). The results of the study revealed that the bonding properties of S-BSCs were optimized when Phenol-Resorcinol-Formaldehyde resin (PRF) was used as the glue, at a spread rate and pressure of 275–300 g/cm2 and 1.2 MPa, respectively. The highest shear strength and wood failure percentage, as well as the lowest boiling delamination rates for two cycles were achieved at a PRF spread rate of around 275–300 g/cm2, under a pressure of 1.0 MPa. which were 24.84 MPa, 90.19%, 0% and 0.77% respectively. On the other hand, the lowest boiling delamination rates of 0.23% and 0.89% for two cycles, respectively were found at a PRF spread rate of 225–250 g/cm2 under a pressure of 1.2 MPa. The study revealed that the values of the MOR and MOE, as well as of CS for the S-BSCs were comparable with those of the BSC samples (146.98 MPa, 14.92 GPa, 125.49 MPa) in the pressure ranges of 144.73–148.10 MPa, 13.77–15.05 GPa, and 120.61–125.86 MPa, respectively. Also, it was found that the mechanical properties of S-BSCs were independent of the type of glue, spread rate, and pressure. Overall, this study determined the effect of secondary bonding process on the bonding and mechanical properties of BSCs.

Full-scale seismic response test on a shallow foundation embedded in tire-derived aggregate for geotechnical seismic isolation

This paper presents results from full-scale tests aimed at characterizing the seismic response of shallow foundations embedded in tire derived aggregate (TDA) with large particle size. The high shear strength, low shear modulus, and high damping ratio of TDA with large particle sizes make it ideally suited for low-cost Geotechnical Seismic Isolation (GSI) systems. Unidirectional shake table tests were performed on a single-degree-of-freedom superstructure connected to a 0.46 m-deep concrete strip footing embedded within a 1.89 m-thick TDA layer inside a laminar box. The TDA-footing system was subjected to a series of sine sweep motions with varying amplitudes and frequencies between 0.4 and 10 Hz. Substantial nonlinearity was observed in the moment-rocking response of the footing, where the specimen experienced rocking stiffness softening at moment demands slightly below its moment capacity. While the footing exhibited moderate transient settlement and uplift during dynamic oscillation, it demonstrated low residual settlement. The TDA layer offered the footing an effective recentering system with an average residual recentering ratio of 0.991. In addition to being low-cost, abundant, and recycled, the TDA layer had both favorable energy dissipation and recentering, with better seismic resilience than structural hinging and conventional foundation rocking systems in soil.

Microstructure, mechanical properties and thermal stability of Al2O3/Al2O3 ceramic matrix composites obtained from submicron-sized powers

Improvement in thermal stability is especially important for the oxide/oxide composites, which are widely applied at high temperatures. Herein, the continuous alumina fiber reinforced alumina matrix (Al2O3/Al2O3) composites were fabricated at 1200–1400 °C using Al2O3 powders with a mean size of 0.6 μm. The Al2O3/Al2O3 composite fabricated at 1300 °C achieved a high flexural strength of 392.9 ± 20.1 MPa and a high interlaminar shear strength of 20.6 ± 1.0 MPa. After exposure at 1000 °C for 100 h and 1400 °C for 10 min, the 1300 °C fabricated Al2O3/Al2O3 composite showed no significant reduction in mechanical properties. A slight decrease in mechanical properties was observed after aging at 1200 °C for 100 h. The high strength retention after the heat treatment benefited from the coarse Al2O3 powders, which could not be easily sintered at high temperatures. This work can expand the selection of the Al2O3/Al2O3 composites for potential applications at service temperatures as high as 1400 °C for a short term.

Recent Developments in Low Temperature Wafer Level Metal Bonding for Heterogenous Integration

The low temperature metal bonding processes (<200°C) are attractive methods for novel applications in 3D packaging with simultaneous formation of electrical interconnections and hermetic encapsulation for microelectromechanical systems.Metal wafer bonding is a generic category of processes consisting of various sub-categories, each one defined by the different principles governing the process. One can differentiate between eutectic wafer bonding (a eutectic bonding layer is formed during process by liquid-solid interdiffusion), intermetallic bonding (an intermetallic alloy is formed as bonding layer during the process by solid-liquid interdiffusion, process known also as Solid Liquid Intermetallic Diffusion – SLID or Transient Liquid Phase – TLP), and metal thermo-compression (TC) wafer bonding.The bonding temperature range for the two types of processes showing liquid interface is relatively narrow (<10-20°C) while for metal TC the bonding temperature range is quite broad (~200°). This important parameter is differentiating the focus in studying the processes: for the low temperature eutectic and SLID/TLP the focus is primarily on the development of new materials systems and secondary on process optimization, while for metal TC the focus is equally shared between metal layers optimization (e.g. fabrication method, oxide management) and process optimization.The SLID bonding process studies were focusing on the Cu–In–Sn, Au–In and Bi–In material systems. It was demonstrated that electrical interconnections can be fabricated at bonding temperatures as low as 150°C by taking advantage of the Cu–In–Sn ternary system. The low processing temperatures allow for bonding of temperature sensitive materials and of materials with dissimilar thermo-mechanical properties by thermally induced stress management. Microstructural characterization confirmed the high bonding quality with low amount of defects in interconnections composed of a layered Cu / intermetallic / Cu structure, with a single-phase intermetallic Cu6(Sn,In)5 phase. Moreover, the mechanical testing shows that the bonds have tensile strength above 30 MPa.Au–In SLID bonding can be performed at temperatures slightly higher than the In melting temperature of 156°C. Successful bonds were demonstrated at 180°C. The resulting intermetallic bonding layer has a remelting temperature >450°C and a high shear strength above 30 MPa both at room temperature and 300°C.Another system studied was Au–In–Bi, utilizing the low eutectic point of In–Bi (72oC). Bonds at temperatures of 90 °C were proven. However, in order to consume the various In–Bi intermetallics with low melting temperatures (T< 110 oC), a bonding temperature higher than 110 oC should be used for a reliable result. We have demonstrated such SLID bonds at 115 oC, with a bond line consisting of Au / Au–In IMCs / Au, with Bi inclusions. All these materials have melting temperatures > 271 oC, with the bonding layer being stable at 450 oC if Bi does not form continuous structures.The study of metal TC bonding is reporting recent developments on the optimization of Cu-Cu and Al-Al wafer bonding. To decrease the bonding temperature of Cu-Cu TC bonding, Cu layers fabrication and oxide management are essential. By using certain surface pre-treatment methods such as plasma and self-assembled monolayer (SAM), Cu-Cu low temperature bonding was investigated. Various plasma concentrations were used to investigate the influence of plasma composition on bond strength.Further investigations were performed on the impact of different morphological Cu-properties and their effects on the bonding yield. The comparison of the interdiffusion behavior of layers deposited using different methods (e.g. physical vapor deposition - PVD Cu vs. electroplated - ECD Cu), as well as different surface preparation methods is being reported here. Different surface treatments like in-situ and ex-situ oxide management, as well as pre-bond CMP processes were tested in combination with the respective deposition methods. By combining the most effective sample and process parameters, the necessary bonding temperature for a successful Cu-Cu TC bonding could be reduced to temperatures of 175°C. The successful interdiffusion behavior at such low temperatures was confirmed by cross section TEM measurements.Apart from Cu, Aluminum is widely used material, due to its good electrical conductivity and compatibility with CMOS processes. Aluminum has a very stable native oxide and therefore high temperature and pressure are necessary to generate a successful Al-Al bond at wafer-level. The low temperature Al-Al TC bonding using a thin Palladium passivation layer at 350°C is reported here. The thermo-compression bonding was performed on both blank and patterned wafers.This work is reviewing recent achievements in the reduction of metal wafer bonding process temperature to less than 200°C based on the mechanical, structural and electrical characterization of the metal bonding layers.

Micro-cones Cu fabricated by pulse electrodeposition for solderless Cu-Cu direct bonding

In the post-Moore’s era, Cu-Cu direct bonding has garnered significant attention as a promising alternative to solder joints for chip interconnection in advanced electronic packaging technology. Its advantages lie in reduced process restrictions and steps, as well as lower bonding temperature, which align with the demands for low cost and high compatibility. In this study, (110)-oriented micro-cones Cu was fabricated via template-free pulse electrodeposition, enabling solderless Cu-Cu direct bonding at 250 ℃ under three distinct bonding pressures without chemical mechanical polishing (CMP). The contact bonding area and shear strength gradually increased corresponding to the applied bonding pressure. Seamless bonding interface was achieved under high bonding pressure, leading to high shear strength of 116.4 MPa for Cu-Cu bonding joints. The obtuse polygon pyramid micro-cones, characterized by an enlarging cross-sectional area from apex to base, coupled with inherent mechanical properties, induce high applied stress at micro-cone’s tip and a low yield stress, facilitating the initiation and propagation of plastic deformation during the bonding process. This study has demonstrated the feasibility of utilizing the micro-cones Cu for low-temperature bonding without CMP treatment, offering valuable insights into the advanced interconnection technologies.

Synthesis and cryogenic performance of closed-loop recycled Al2O3/epoxy resins composites

The non-degradability of epoxy present environmental and economic challenges. This study synthesized a degradable epoxy resin with ester bonds using a novel method. The synthesized resin was mixed with KH560-modified micro-sized spherical α-Al2O3 particles at different concentrations to produce the A-TPHE. The cured A-TPHE exhibited excellent mechanical properties, including high tensile and shear strength (∼100 MPa), as well as outstanding impact resistance. Furthermore, DMA, DSC, and TGA analyses revealed that the composites had a high glass transition temperature (>100 °C) and good thermal stability. Notably, the A-TPHE80 % filler achieved a favorable thermal conductivity of 1.2 W/mK at 77 K. A-TPHE also demonstrated good insulation properties. The degradation of the resins was assessed at 30 wt% NaOH, and the recovered filtrate facilitated closed-loop recycling of the composite material with a consistent recovery rate exceeding 70 %. In conclusion, this study establishes a foundation for the application of degradable thermosetting materials in cryogenic environments.

Low-temperature packaging through Ag-Cu supersaturated solid solution nanoparticle paste for high-temperature power electronics

In this work, anti-oxidative single-phase Ag-Cu supersaturated solid-solution nanoparticles (Ag-Cu SS-NPs) were synthesized by a one-step method to serve as packaging materials for high-temperature power electronics. After sintering at 250 ℃ in air, a dense supersaturated structure with nano-sized Cu precipitates and coherent twins, high shear strength over 133 MPa and low resistivity (4.35 μΩ·cm) were obtained. Notably, the supersaturated structure with nano-sized Cu precipitates enhanced the thermomechanical properties and high-temperature stability. The high-temperature shear strengths of the sintered Ag-Cu joints reached remarkable 93.5 MPa at 300 ℃. Meanwhile, the room-temperature shear strength of the sintered Ag-Cu SS-NP joints after aging at 300 ℃ for 500 h was maintained at 98.7 MPa, doubling that of the sintered Ag joints. Hence, the Ag-Cu SS-NP paste presents excellent feasibility and potential for high-temperature power electronics.

Soil microbial improvement using enriched vinasse as a new abundant waste

This study proposes the use of vinasse, an inexpensive and readily available waste biopolymer, as a fundamental component of a waste culture medium that can enhance the effectiveness and cost-efficiency of the microbial-induced calcite precipitation (MICP) method for sustainable soil improvement. Vinasse enriched with urea, sodium caseinate, or whey protein concentrate is employed to optimize bacterial growth and urease activity of Sporosarcina pasteurii (S. pasteurii) bacterium. The best culture medium is analyzed using Taguchi design of experiments (TDOE) and statistical analysis, considering the concentration of vinasse and urea as effective parameters during growth time. To test the best culture medium for bio-treated soil, direct shear tests were performed on loose and bio-treated sand. The results demonstrate a substantial cost reduction from $0.455 to $0.005 per liter when using the new culture medium (vinasse and urea) compared to the conventional Nutrient Broth (NB) culture medium. Additionally, the new medium enhances soil shear strength, increasing the friction angle by 2.5 degrees and cohesion to 20.7 kPa compared to the conventional medium. Furthermore, the recycling of vinasse as a waste product can promote the progress of a circular economy and reduce environmental pollution. As ground improvement is essential for many construction projects, especially those that require high shear strength or are built on loose soil, this study provides a promising approach to achieving cost-effective and sustainable soil microbial improvement using enriched vinasse.

Enhanced shear strength of Cu/AlN/Cu gradient materials with continuous and quasi‐continuous interfacial structures

AbstractIn the electronic industry, the composite of copper (Cu) and aluminum nitride (AlN) is widely used, but obtaining Cu/AlN/Cu functionally gradient materials (Cu/AlN/Cu FGMs) in a single step using traditional laminated sintering processes has proven challenging due to significant differences in their physical properties. To address this issue, molybdenum (Mo), with a high melting point and low expansion, was involved in creating a continuous gradient structure with AlN and a quasi‐continuous interfacial structure with Cu. The continuous interfacial structure of Mo/AlN gradient materials was obtained by hot pressing at 1650°C. Subsequently, the quasi‐continuous interfacial structure of Cu/Mo heterogeneous metal joints with high shear strength was achieved by utilizing the diffusion welding method at 700–950°C. The results indicated that the optimum shear strength of Cu/AlN/Cu FGMs is around 90 MPa. However, Cu/AlN/Cu FGMs with different diffusion interlayers failed in different ways when shear occurred, which greatly depends on the phase compositions at the joint. The challenges are overcome by utilizing Mo to construct the continuous and quasi‐continuous interfaces, resulting in Cu/AlN/Cu FGMs with improved shear properties.

Processing and Reliability Testing of a Copper Pressure Sinter Paste for use in High Power Module, Die Attach Applications

Power electronics are evolving to meet the high demands of new and emerging applications such as e-mobility/vehicle electrification. Pressure sintered silver is fast becoming the material of choice for die attach due the favorable material properties and proven reliability. This paper will introduce a copper sinter paste that can achieve consistently high shear strengths ~40MPa when sintered with 15-20MPa of pressure. The impact of process conditions is examined, plus reliability testing. Aging tests at 250ᵒC for more than 1000 hours show an increase in shear strength compared to time zero. TCT of -40ᵒC to 175ᵒC was done for &gt;3000 cycles, no delamination was observed and again the shear strength was shown to increase through TCT. Microstructure analysis of the sinter layer is compared at time zero and after 1000 and 2000 cycles of TCT.

An eco‐friendly and high shear strength adhesive from catechol‐modified polyethyleneimine

AbstractConventional adhesives often emit volatile organic compounds (VOCs), which have a negative impact on human health. In this paper, an environmentally‐friendly supramolecular adhesive PD which has high adhesive and low VOCs emission is prepared by the reaction between polyethyleneimine (PEI) and 3,4‐dihydroxybenzaldehyde (DBA). PD containing abundant catechol groups exhibit excellent adhesion to wood substrates and is able to reach a maximum shear strength of 5.20 ± 0.39 MPa. One factor is attributed to multiple reactions between PEI, and DBA and oxidation of DBA. These reactions construct a complex three‐dimensional cross‐linked structure which is very helpful to improve the bonding performance of the adhesive. Another reason refers to the fact that a large number of catechol groups in PD can form a lot of hydrogen bonds with the amino group in PEI and the hydroxyl group in the wood substrate. These hydrogen bonds play an important role in enhancing shear strength. PD adhesives have a stronger bond strength than commercial chloroprene rubber (CR, Pattex‐PXL) and polyvinyl acetate adhesives (PVAc, JUJU‐8708) and have lower emissions of VOCs. As an environmentally‐friendly adhesive for wood‐based substrates, this adhesive may have potential applications in the wood processing industry.

Utilization of Ionic Organic Polymer to Improve Performance and Properties of Problematic Soils

Problematic soils with high compressibility and low shear strength are often treated with traditional chemical stabilizing additives such as cement and lime to improve their engineering properties. Polymers were employed to improve and reinforce a variety of material qualities in a wide range of applications. The use of polymer SBS (stabilizer base stabilizer) to improve the characteristics of problematic soils is discussed in this research. Two types of soils were used. The first type, "soil A Burj," is collapsible soil and was collected from Burj El-Arab city, while the second type, "soil B Dam," is fine sand and was obtained from Damietta city. The untreated and treated samples were subjected to sieve analysis, hydrometer, liquid limits, standard compaction, collapse potential (CP), direct shear, California Bearing Ratio (CBR) testing, and SEM, TEM, chemical, and microstructural analysis tests. Three different polymer SBS concentrations in water were used (1:300, 1:150, and 1:10). The results showed that by adding the polymer SBS, LL and OWC decreased exhibiting more plastic behavior compared to the non-treated samples. Also, the CP decreased with adding the polymer SBS, and the degree of collapsibility was enhanced from trouble to moderate trouble condition. The shear strength, internal friction angle, and CBR value were also improved. In summary, the best results were produced when a polymer ratio of 1:150 was used and a curing time of at least 28 days was provided. Doi: 10.28991/CEJ-2023-09-12-05 Full Text: PDF

The Development of a Draft Force Prediction Model for Agricultural Tractors Based on the Discrete Element Method in Loam and Clay Loam

In the field of agricultural machinery, various empirical field tests are conducted to measure design loads for the optimal design and implementation of tractors. However, conducting field tests is costly and time-consuming, with many constraints on weather and field soil conditions, and research utilizing simulations has been proposed as an alternative to overcome these shortcomings. The objective of this study is to develop a DEM-based draft force prediction model that reflects differences in soil properties. For this, soil property measurements were conducted in two fields (Field A in Daejeon, Republic of Korea, and Field B in Chuncheon, Republic of Korea). The measured properties were used as parameters for DEM-based particle modeling. For the interparticle contact model, the EEPA contact model was used to reflect the compressibility and stickiness of cohesive soils. To generate an environment similar to real soil, particle mass and surface energy were calibrated based on bulk density and shear torque. The soil property measurements showed that Field B had a higher shear strength and lower cone index and moisture content compared to Field A. The actual measured draft force was 19.47% higher in Field B than in Field A. In this study, this demonstrates the uncertainty in predicting draft force by correlating only one soil property and suggests the need for a comprehensive consideration of soil properties. The simulation results of the tillage operation demonstrated the accuracy of the predicted shedding force compared to the actual field experiment and the existing theoretical calculation method (ASABE D497.4). Compared to the measured draft force in the actual field test, the predictions were 86.75% accurate in Field A and 74.51% accurate in Field B, which is 84% more accurate in Field A and 37.32% more accurate in Field B than the theoretical calculation method. This result shows that load prediction should reflect the soil properties of the working environment, and is expected to be used as an indicator of soil–tool interaction for digital twin modeling processes in the research field of bio-industrial machinery.