Compressive Surface Research Articles

Increasing Fracture Toughness and Transmittance of Transparent Ceramics using Functional Low-Thermal Expansion Coatings

Transparent polycrystalline ceramics have the potential to enable applications no other materials can, but to do so their strength and toughness must be improved. However, surface strengthening treatments like those used for glasses have so far remained elusive. Here for the first time, we report on engineering unprecedented surface compression, of the magnitude achieved for ion-exchange strengthened glasses (~750 MPa) in transparent ceramics. This was achieved by applying functional, low thermal-expansion yttria coatings onto yttria-stabilized zirconia substrates and thermally treating. In some instances, the treatment more than doubled the fracture toughness while simultaneously increasing light transmittance.

Three‐dimensional (3D) flexible nanofibrous network knitting on hierarchical porous architecture

AbstractHierarchical structured porous ceramics have attracted tremendous research interests because of their numerous excellent properties including robust mechanical strength and large surface area. In this work, silicon carbide (SiC)‐based porous ceramics with three levels of pore hierarchy are fabricated from silicon particle‐stabilized foams and a subsequent one‐step calcination after they were embedded with coke. Three‐dimensional (3D) flexible nanofibrous network is adhered and wrapped on cell walls of porous ceramics, which is readily fine‐tuned and tailored by the temperature to provide optimized pore structure. The resultant SiC‐based porous ceramics present a density of 1.03 g/cm3 at a porosity of 72% with a large quantity of hierarchical micro‐ and macropores. This hierarchical structure leads to robust compressive strength (23.52 MPa) and large surface area (64.32 m2/g). The fabrication method is straightforward and sought‐after, providing a facile technical route for advanced hierarchical porous ceramics used in filtration and catalysis fields.

Ion release, antimicrobial and physio-mechanical properties of glass ionomer cement containing micro or nanosized hexametaphosphate, and their effect on enamel demineralization.

To evaluate the effects of hexametaphosphate microparticles (mHMP) or nanoparticles (nHMP) incorporated in glass ionomer cement (GIC) on antimicrobial and physico-mechanical properties, fluoride (F) release, and enamel demineralization. HMP solutions were obtained at concentrations of 1, 3, 6, 9, and 12%, for screening of antimicrobial activity. Next, mHMP or nHMP at 6, 9, and 12% were incorporated into a resin-modified GIC and the antibacterial activity was evaluated. The resistance to diametral tensile and compressive strength, surface hardness, and degree of monomer conversion as well as F and HMP releases of GICs were determined. Furthermore, specimens were attached to enamel blocks and submitted to pH-cycling, and mineral loss was determined. Parametric and non-parametric tests were performed, after checking data homoscedasticity (p < 0.05). HMP solutions at 6, 9, and 12% demonstrated the best antibacterial activity. GIC containing HMP showed better antibacterial effects at 9 and 12% for nHMP. Regarding F and HMP releases, the highest levels of release occurred for groups containing 9 and 12% nHMP. With the increase in HMP concentration, there was lower mineral loss. However, the incorporation of mHMP or nHMP in GIC reduced values of physico-mechanical properties when compared to the control GIC. nHMP improves antimicrobial activity and fluoride release, and decreases enamel demineralization, but reduces the physico-mechanical properties of GIC. The association of GIC/HMP could be an alternative material for patients at high risk for dental caries and could be indicated for low-stress regions or provisional restorations.

Trapped Aqueous Films Lubricate Highly Hydrophobic Surfaces.

Friction at hydrophobic surfaces in aqueous media is ubiquitous ( e.g., prosthetic implants, contact lenses, microfluidic devices, biological tissue) but is not well understood. Here, we measure directly, using a surface force balance, both normal stresses and sliding friction in an aqueous environment between a hydrophilic surface (single-crystal mica) and the stable, molecularly smooth, highly hydrophobic surface of a spin-cast fluoropolymer film. Normal force versus surface separation profiles indicate a high negative charge density at the water-immersed fluoropolymer surface, consistent with previous studies. Sliding of the compressed surfaces under water or in physiological-level salt solution (0.1 M NaCl) reveals strikingly low boundary friction (friction coefficient μ ≈ 0.003-0.009) up to contact pressures of at least 50 atm. This is attributed largely to hydrated counterions (protons and Na+ ions) trapped in thin interfacial films between the compressed, sliding surfaces. Our results reveal how frictional dissipation may occur at hydrophobic surfaces in water and how modification of such surfaces may suppress this dissipation.

Glass-frit bonding of silicon strain gages on large thermal-expansion-mismatched metallic substrates

Bonding of silicon strain gages on stainless-steel substrates is a critical issue in diaphragm-type pressure sensors because of the large mismatch in coefficients of thermal expansion between silicon and metal resulting in serious reliability problems. A new method to significantly improve the glass-frit bonding of silicon gages on metal diaphragms is reported based on an intermediate thin glass plate onto which silicon strain gages are fabricated. The glass interlayer enables very reliable bonds without post-bond misalignment, debonding, or cracking through the selection of glasses that very closely match silicon and the compressive surface strengthening of glasses. Furthermore, the proposed gage structure provides great improvement in the electrical performance, especially the thermal drifts of offset (zero) and span of Si strain-gage-based bridge transducers.

Bending Behavior of a Wrought Magnesium Alloy Investigated by the In Situ Pinhole Neutron Diffraction Method

The tensile twinning and detwinning behaviors of a wrought magnesium alloy have been investigated during in situ four-point bending using the state-of-the-art high spatial resolution pinhole neutron diffraction (PIND) method. The PIND method allowed us to resolve the tensile twinning/detwinning and lattice strain distributions across the bending sample during a loading-unloading sequence with a 0.5 mm step size. It was found that the extensive tensile twinning and detwinning occurred near the compression surface, while no tensile twinning behavior was observed in the middle layer and tension side of the bending sample. During the bending, the neutral plane shifted from the compression side to the tension side. Compared with the traditional neutron diffraction mapping method, the PIND method provides more detailed information inside the bending sample due to a higher spatial resolution.

Residual stress distribution in tempered glass with reground edges

Many glass applications require laminated glass to achieve a safe load-bearing behaviour. Beside the structural aspect, glass elements have to meet high aesthetic demands. Laminated glasses often feature an offset between the individual glass panes resulting from the lamination process. With regards to visible or exposed edges, this displacement reduces the aesthetic quality of the glass component. The regrinding of the edge after lamination equalises the offset and thus creates a smooth surface. However, regrinding tempered glass leads to a reduction of the surface compression zone at the edge and may decrease the load-bearing capacity. A research project focuses on the detailed evaluation of the effect of regrinding tempered glass. To attain a precise understanding, three different aspects have to be examined: first the maximum required grinding depth resulting from the edge offset, second the defects on the surface of the edge and third the residual stress distribution. The third part was examined by means of stress measurements at the edge and the surface of different specimens. Glass beams made of fully tempered glass and heat strengthened glass with three different thicknesses (6, 8 and 10 mm) were ground after the tempering process. The regrinding depth was 1, 2 and 3 mm. One group of specimens remain untreated as a reference. The depth of the compression zone and the magnitude of the surface stress at the edge were measured with the help of photoelastic measurements. The experimental approach and the results are the content of this paper. It enables a statement about transformations of the residual stress state at the edge owing to regrinding tempered glass.

The development of a low carbon binder produced from the ternary blending of cement, ground granulated blast furnace slag and high calcium fly ash: An experimental and statistical approach

This research aims to develop a new, environmentally friendly, cementitious material by blending Ordinary Portland Cement (OPC), Ground Granulated Blast Furnace Slag (GGBS) and High Calcium Fly Ash (HCFA). Compressive strength and electrical resistivity tests were used to evaluate the mortars’ performance. A multi-regression (MR) model was also utilised to study the effects of curing time and content of OPC, GGBS and HCFA on the mortars’ strength and to identify the relationship between measured and predicted compressive strengths. The results indicated that the newly developed binder was composed of 35 wt% OPC, 35 wt% GGBS and 30 wt% HCFA that showed a compressive strength and surface electrical resistivity of 30.8 MPa and 103.5 kΩ.cm after 56 days of curing, respectively. Significant changes in the microstructure of the developed binder paste over curing time were evidenced by SEM imaging. The statistical analysis indicated that the influence of the parameters examined on the development of the mortars’ compressive strength could be modelled with a coefficient of determination, R2 of 0.893, and that the relative importance of these parameters followed the order curing time (t) > HCFA% > OPC% > GGBS%. This new binder could contribute significantly to decreasing the cost of construction materials and to reducing CO2 emissions.

Design of hypersonic forebody with submerged bump

A double shock waverider forebody configuration, with curved surfaces and known pressure fields and shock arrays, is constructed by a stream-tracing approach. The compression surface consists of a wedge and conical shocks. The conical shock results from a modified wave-derived bump surface that diverts the boundary layer before the inlet entrance. The design is fully computational fluid dynamics based and emphasis is placed on the compact design with boundary layer diverting ability. Controlling or diverting the thick boundary layer safely is a difficult challenge in hypersonic flight vehicle design especially when the inlets are highly integrated with the fuselage. Numerical simulations show that the new combination can divert a significant fraction of boundary layer before the inlet and maintains a good compression ratio for propulsion efficiency at Mach 5.0. Effects of forebody aerodynamics on the integrated inlet and comparisons with other systems are described in this paper.

Predicting meniscal tear stability across knee-joint flexion using finite-element analysis

PurposeTo analyse the stress distribution through longitudinal and radial meniscal tears in three tear locations in weight-bearing conditions and use it to ascertain the impact of tear location and type on the potential for healing of meniscal tears.MethodsSubject-specific finite-element models of a healthy knee under static loading at 0°, 20°, and 30° knee flexion were developed from unloaded magnetic resonance images and weight-bearing, contrast-enhanced computed tomography images. Simulations were then run after introducing tears into the anterior, posterior, and midsections of the menisci.ResultsAbsolute differences between the displacements of anterior and posterior segments modelled in the intact state and those quantified from in vivo weight-bearing images were less than 0.5 mm. There were tear-location-dependent differences between hoop stress distributions along the inner and outer surfaces of longitudinal tears; the longitudinal tear surfaces were compressed together to the greatest degree in the lateral meniscus and were most consistently in compression on the midsections of both menisci. Radial tears resulted in an increase in stress at the tear apex and in a consistent small compression of the tear surfaces throughout the flexion range when in the posterior segment of the lateral meniscus.ConclusionsBoth the type of meniscal tear and its location within the meniscus influenced the stresses on the tear surfaces under weight bearing. Results agree with clinical observations and suggest reasons for the inverse correlation between longitudinal tear length and healing, the inferior healing ability of medial compared with lateral menisci, and the superior healing ability of radial tears in the posterior segment of the lateral meniscus compared with other radial tears. This study has shown that meniscal tear location in addition to type likely plays a crucial role in dictating the success of non-operative treatment of the menisci. This may be used in decision making regarding conservative or surgical management.

Increase in Strength and Fretting Resistance of Alloy 718 Using the Surface Modification Process

This work comparatively investigated the strength (hardness, yield strength, dynamic elastic modulus, and surface residual stress), fretting failure, and corrosion resistance of the as-received and treated Ni-based superalloy Alloy 718. The goal of the current research is to improve the hardness, fretting wear, and corrosion resistances of Alloy 718 through the ultrasonic nanocrystal surface modification (UNSM) process with the aim of extending the lifespan of aircraft and nuclear components made of Alloy 718. The experimental results revealed that the surface hardness increased by about 32%, the fretting wear resistance increased by about 14%, and the corrosion resistance increased by about 18% after UNSM process. In addition, the UNSM process induced a tremendous high compressive surface residual stress of about −1324 MPa that led to an increase in yield strength and dynamic Young’s modulus by about 14 and 9%, respectively. Grain size refinement up to ~50 nm after the UNSM process is found to be responsible for the increase in surface hardness as well. The depth of the effective layer generated by the UNSM process was about 20 µm. It was concluded that the UNSM process played a vital role in increasing the strength and enhancing the corrosion and fretting resistances of Alloy 718.

SCOPE OF GRANULATED BLAST FURNACE SLAG AS FINE AGGREGATE IN CONCRETE FOR NORMAL AND FIRE EXPOSURE

Present work experimentally investigates the scope of utilizing granular blast furnace slag (GBFS) in concrete exposed to high temperature. Six series of concrete mixes of Grade M20 including control mix were prepared by replacing natural sand with GBFS in 10, 30, 50, 70 and 100% by weight. Sustainability of GBFS concrete for normal weather condition was ensured by preliminary investigation on mechanical strength for various GBFS concrete mixes at various ages. Later, fire durability of the concrete was evaluated by residual compressive strength, weight loss and surface observation of heat cured specimen through necked eye. Cube compressive strength improves by 2.15-6.31% while cylindrical compressive strength of concrete mix with 30% GBFS marginally improves at all ages. Split strength increases up to 2.9-8.07% up to 50% GBFS replacement while flexure strength increases by 0.81-7.0% at 30% with respect to all the age of curing at room temperature. Residual compressive strengths were 57.3, 55.89 and 54.46 % for 30, 50 and 70% GBFS concrete mixes at 600°C. Surface cracks in specimen were observed after 500°C which continued to grow with the increase in temperature. Furthermore, test results indicate the improvement in the properties of concrete with the incorporation of GBFS even though it exposes to high temperature.

Design of top mounted supersonic inlets for a cylindrical fuselage

Designing an inlet based on the fuselage geometry and its constraints is an important part of flight vehicle design. Among the different possible configurations, design integration of a supersonic inlet with a cylindrical fuselage is a major challenge. On one hand, propulsive efficiency requirements force the designers to consider the simplest compression surfaces for the inlet entrance geometries and on the other hand, the considerable drag of inlet/diverter integrations needs to be minimized, which can affect the inlet. In this paper, two new concepts as a replacement for a top mounted pitot inlet are presented: a three-dimensional wave-derived inlet and a trigonometric bump inlet. They are designed based on computational fluid dynamics simulations and their performance has been measured and compared with the initial single normal shock inlet as a baseline.

Molecular organization relationship of low-bandgap polymers at the air-water interface and in solid films

Low-bandgap organic polymers, poly[(4,4‑bis(2‑ethylhexyl)cyclopenta‑[2,1‑b:3,4‑b′]dithiophene)2,6‑diyl‑al‑(2,1,3‑benzothiadiazole)‑4,7‑diyl](PCPDTBT), and poly [(4,4′‑dioctyldithieno[3,2‑b:2′,3′d]silol‑2,6‑diyl)‑alt‑(2,1,3‑benzothiadiazole)‑4,7‑diyl)], (Si-PCPDTBT) were analyzed at the air-water interface forming a Langmuir monolayer. In order to form stable monolayers and to transfer to solid supports, amphiphilic molecules of stearic acid (SA) were mixed with them. For the pristine polymers, the floating monolayers were transferred onto solid substrates via the Langmuir-Schaefer (LS) technique. Surface pressure-area isotherms and compressibility modulus curves demonstrated that the SA incorporation to the polymers at the air-water interface modified the rheological properties of the Langmuir films, since the films became less compressible at higher pressures and there is clear conformational reorganization taking place at intermediary pressures. The UV–Vis absorption also depicted the changes on the overall film morphology by the shift on the maximum absorption bands, and along with cyclic voltammetry curves the absorption spectra made it possible to estimate the energy diagrams for the polymers. Photoconductivity effects were observed for all the sample, among which the pristine polymers fabricated by LS showed better results, suggesting that the organization provided by the Langmuir-Blodgett (LB) technique was not enough to overcome the insulating characteristic of the SA molecules in this specific configuration.

Numerical investigation of bleeding control method on section-controllable wavecatcher intakes

The bleeding control method and analysis of advantages, challenges on wavecatcher (inward turning) intakes are investigated in this paper. Firstly, a quantitative analysis on the substantial advantages of wavecatcher intakes for ramjet is presented comparing to two-dimensional planar symmetry compression. According to the results, with the same parameters in the entrance and exit section, the total pressure recovery of Internal Conical Flow of C increases by 28.0%; the compression surface length decreases by 5%; the wetted area decreases by 15.7% and the pressure drag decreases by 12.1%. However, due to high compressive efficiency of wavecatcher intake, the boundary layer experiences a higher adverse pressure gradient, contributing to enhance shock wave/boundary layer interaction (SBLI). Secondly, the effects of bleeding control on wavecatcher intake are elucidated by numerical simulations. The bleeding control improves the flow structures by decreasing the boundary layer thickness to weaken the SBLI and bleeding the spanwise vortex out. Furthermore, due to the weak interaction, the terminal shock wave is stable closely behind the throat section, increasing the resistance against the back pressure, decreasing the Mach number before the terminal shock wave and improving the total pressure recovery of the exit section by 3.73% relatively.

Light enhanced direct Cu bonding for advanced electronic assembly

An innovative and efficient surface modification pre-treatment that enhances Cu–Cu direct bonding through electromagnetic irradiation, including pulsed Xenon flash and near infrared rays is proposed. Without vacuum, short but critical electromagnetic radiation exposure on faying faces prior to bonding can significantly improve the joint strength up to 50% or even more. Copper atom diffusion acceleration by increased compressive residual surface stresses resulting from sudden heating/cooling accounts for the joint reinforcement. A close relationship between the increase in joint strength and the change in surface physics properties due to electromagnetic irradiations can be found.

A Scramjet Compression System for Hypersonic Air Transportation Vehicle Combined Cycle Engines

This paper proposes a compression system for a scramjet, to be used as part of a combined cycle engine on a hypersonic transport vehicle that can achieve sustained flight at 8 Mach 8. Initially research into scramjet compression system and shock wave interaction was conducted to establish the foundation of the scramjet inlet and isolator sections. A Computational Fluid Dynamics (CFD) campaign was conducted, where the shock structure and flow characteristics was analysed between Mach 4.5–8. The compression system of a scramjet is of crucial importance in providing air at suitable Mach number, pressure and temperature to the combustion chamber. The use of turbojet engines in over-under configuration with the scramjet was investigated as well as the study of a combined cycle scramjet-ramjet configuration. It was identified that locating the scramjet in the centre with a rotated ramjet on either side, where its ramps make up the scramjet wall was the most optimal configuration, as it mitigated the effect of the oblique shocks propagating from the scramjet walls into the adjacent ramjet. Furthermore, this meant that the forebody of the vehicle could solely be used as the compression surface by the scramjet. In this paper, the sizing of the scramjet combustion chamber and nozzle were modified to match the flow properties of the oncoming flow with the purpose of producing the most optimum scramjet configuration for the cruise speed of Mach 8. CFD simulations showed that the scramjet inlet did not provide the levels of compression and stagnation pressure recovery initially required. However, it was found that the scramjet provided significantly more thrust than the drag of the aircraft at sustained Mach 8 flight, due to its utilisation of a very aerodynamic vehicle design.

Effects of seat parameters and sitters’ anthropometric dimensions on seat profile and optimal compressed seat pan surface

Designing one seat for multi-sitters and multi-activities is challenging especially in a very restrained aircraft economy class cabin. In this paper, the effects of seat parameters and sitters' anthropometric dimensions on seat profile and optimal compressed seat pan surface were studied using a newly built multi-adjustable experimental seat. The ‘optimal’ seat pan contact surface was obtained by controlling the height of 52 cylinders so that the normal contact force was distributed to all cylinders as evenly as possible. With 13 other motorized adjustments controllable by a computer, individual seat profile in the symmetry plane such as seat height, seat pan length, seat pan angle, lumbar protrusion and headrest position were also studied. Data were collected from 36 men and women of varying body size testing 40 seat configurations. Parametric models were obtained for predicting seat profile and optimal compressed seat pan seat surface in function of seat pan and back rest angles for two sitting postures. It is expected that the proposed parametric models provide necessary reference values in seat development for a better fit of a target population of sitters with large varying body size.

Quaternized xylan/cellulose nanocrystal reinforced magnetic hydrogels with high strength

Recently, ever-increasing focus has been on the exploration of high-strength and intelligent hydrogels. In this paper, we demonstrate a feasible approach to prepare magnetic hydrogels with high compression strength, elasticity and elongation by a two-step process. Quaternized xylan (QXH) and cellulose nanocrystal (CNC) could form the ionic crosslinking within the network to enhance the mechanical strength of hydrogels. Subsequently, Fe3O4 nanoctahedra was fabricated in situ within the reinforced hydrogel matrix. Properties of prepared hydrogels including the compressive strength, swelling ratio, magnetic performance, thermal stability, surface morphology and adsorption capacity for heavy metal ions from the aqueous solution were investigated. Results showed that QXH and CNC had the significant impact on improving the strength property of hydrogels. The compressive stress of prepared hydrogel was sharply increased to the limit of the measurement (2.5 MPa), when the compressive strain reached 85%. This hydrogel also maintained 90% original strength after compression for 30 times. The maximum tensile elongation of this hydrogel was 2875%, corresponding to the breaking tensile strength of 73.86 kPa. Prepared hydrogels also showed the good absorption capacity for heavy metal ions.

Effect of electrode material on piezoelectric output of PVDF sensor with electrospun nanofiber web

The electrospun PVDF (Polyvinylidene Fluoride) nanofiber web is commonly agreed on a kind of new sensitive materials for the sensor testing the dynamic pressure and energy harvesting, and has the characteristics of fast response and high sensitivity of pressure. As a result of the nanofiber web, it must be packaged to collect piezoelectric charge and bear strong mechanical behavior before industrial practice. The packaging of PVDF nanofiber web is usually sandwiched by incorporating a pair of flexible electrode. However, the effects of the surface and mechanical properties of electrodes such as morphology, roughness and compressibility have not been well investigated yet. This work will introduce three common types of packaging electrode materials (adhesive copper foil tape, indium tin oxide (ITO) thin film, adhesive conductive cloth.) in previously published literatures, compares the piezoelectric output of their sensor prototypes under a periodic impact, and discusses the effect of surface morphology, electrical resistance, and compressibility. The results showed that it has higher output of PVDF piezoelectric sensor packaged by electrode materials with the smooth surface and low mechanical compressibility. This result provides a guideline for designing the textile electrode material for the PVDF nanofiber web.