High Compressive Stress Research Articles

Isotropic etching polishing of belt ground Inconel 718 to improve surface strengthening and quality

Belt grinding (BG), widely used in Inconel 718 machining, can result in desired surface strengthening. However, the grinding-induced strengthening effect diminishes in subsequent belt polishing (BP), thus deserving special attention. This paper proposes isotropic etching polishing (IEP) as an alternative finishing process to effectively retain the robotic BG strengthened layer and concurrently improve the surface quality of BG Inconel 718. The strengthening effect and quality of surface layers processed by BG, BG + BP and BG + IEP are systematically compared and evaluated. The results indicate that BG can introduce an ~150-μm-thickness gradient strengthened layer, featured by high microhardness, significant domain refinement, large microstrain increment, high residual compressive stress, and a strong 〈100〉 texture. The optimized IEP retains approximately 86.1% (maximum) of the strengthening effect and 75.1% of the BG strengthened layer. The microhardness of the BG + IEP surface reaches 523 HV, which is about 6 times higher than that of the BG + BP surface. The BG + IEP surface of superior quality is very smooth (platykurtic) and clean, in contrast to the rough and defective BG + BP surface. The IEP is proposed to be an effective way to simultaneously realize the BG strengthened layer retention and the surface quality improvement.

Preparation and Properties of Double Network Hydrogel with High Compressive Strength.

In this work, p–double network (p–DN) hydrogels were formed by the interpenetration of poly(2–acrylamide–2–methylpropanesulfonic acid–copolymer– acrylamide) microgel and polyacrylamide. The initial viscosity of prepolymer solution before hydrogel polymerization, mechanical properties, temperature and salt resistance of the hydrogels were studied. The results showed that the initial viscosity of the prepolymer was less than 30 mP·s, and the p–DN hydrogel not only exhibited high compressive stress (37.80 MPa), but the compressive strength of p–DN hydrogel could also reach 23.45 MPa after heating at 90 °C, and the compressive strength of p–DN hydrogel could reach 13.32 MPa after soaking for 24 h in the solution of 5W mineralization. In addition, the cyclic loading behavior of hydrogel was studied. The dissipation energy of p–DN hydrogel under 80% strain was 7.89 MJ/m3, which effectively dissipated energy. Meanwhile, p–DN hydrogel maintained its original form while breaking the pressure greater than 30 MPa, indicating excellent plugging performance.

An investigation into the mechanistic origin of thermal stability in thermal-microstructural-engineered additively manufactured Inconel 718

An obstacle hindering the applicability of surface modification techniques such as laser peening (LP) in high temperature systems stems from thermally-driven degradation of desirable, strain-induced material modifications. Illustrated in this work is a novel LP scheme termed laser peening plus thermal microstructure engineering (LP + TME) comprised of cyclic LP and the addition of intermittent 600 °C (0.55Tm) heat treatments designed to impart thermally-stable microstructural modifications in additively manufactured (AM) Inconel 718 (In718). Instrumented microindentation uncovered significant surface and sub-surface hardness enhancements exceeding 600 HV following LP + TME, a 20% increase over the as-built material. High magnitude compressive residual stresses exceeding −310 MPa were also measured following a 350-h 600 °C thermal exposure; a 25% increase compared to the material subjected to only a single laser shot. Thermal stabilization and overall material enhancement were determined to be the result of the formation of thermally-stable subgrains, subgrain and grain growth regulation through pinning effects, and dislocation-precipitate interactions.

Chitosan Based Aerogels with Low Shrinkage by Chemical Cross-Linking and Supramolecular Interaction.

Chitosan (CTS) aerogel is a new type of functional material that could be possibly applied in the thermal insulation field, especially in energy-saving buildings. However, the inhibition method for the very big shrinkage of CTS aerogels from the final gel to the aerogel is challenging, causing great difficulty in achieving a near-net shape of CTS aerogels. Here, this study explored a facile strategy for restraining CTS-based aerogels’ inherent shrinkage depending on the chemical crosslinking and the interpenetrated supramolecular interaction by introducing nanofibrillar cellulose (NFC) and polyvinyl alcohol (PVA) chains. The effects of different aspect ratios of NFC on the CTS-based aerogels were systematically analyzed. The results showed that the optimal aspect ratio for NFC introduction was 37.5 from the comprehensive property perspective. CTS/PVA/NFC hybrid aerogels with the aspect ratio of 37.5 for NFC gained a superior thermal conductivity of 0.0224 W/m·K at ambient atmosphere (the cold surface temperature was only 33.46 °C, despite contacting the hot surface of 80.46 °C), a low density of 0.09 g/cm3, and a relatively high compressive stress of 0.51 MPa at 10% strain.

Effect of substrate temperature on sputter-deposited boron carbide films

Sputter deposition of B4C films with tailored physical properties remains a challenge. Here, we systematically study how substrate temperature influences the properties of B4C films deposited by direct current magnetron sputtering onto planar substrates held at temperatures in the range of 100−510°C. Results show that all films are amorphous stoichiometric B4C, with low O content of ∼1 at. %. Films deposited onto substrates at 100°C exhibit high compressive residual stress and decreased mechanical properties. For elevated substrate temperatures in the range of 180−510°C, film mass density, surface roughness, Young’s modulus, and hardness are weakly dependent on substrate temperature. However, in this temperature range, an increase in substrate temperature leads to larger residual compressive stress accompanied by a corresponding reduction in the concentration of nanoscale inhomogeneities. At least for the landing atom ballistics conditions studied here, a substrate temperature range of ∼185−250°C is optimum for growing films with near-zero intrinsic residual stress. The overall weak substrate temperature dependence of film properties revealed in this work is favorable for the development of a robust deposition process, particularly for the case of deposition onto non-planar substrates where temperature control is often challenging.

A new method for high resolution curvature measurement applied to stress monitoring in thin films

By combining the well-known grid reflection method with a digital image correlation algorithm and a geometrical optics model, a new method is proposed for measuring the change of curvature of a smooth reflecting substrate, a common reporter of stress state of deposited layers. This tool, called Pattern Reflection for Mapping of Curvature (PReMC), can be easily implemented for the analysis of the residual stress during deposition processes and is sufficiently accurate to follow the compressive-tensile-compressive stress transition during the sputtering growth of a Ag film on a Si substrate. Unprecedented resolution below 10−5 m−1 can be reached when measuring a homogeneous curvature. A comparison with the conventional laser-based tool is also provided in terms of dynamical range and resolution. In addition, the method is capable of mapping local variations in the case of a non-uniform curvature as illustrated by the case of a Mo film of non-uniform film thickness under high compressive stress. PReMC offers interesting perspectives for in situ accurate stress monitoring in the field of thin film growth.

Robust mechanical properties and corrosion resistance of new low-cost hot-forged and aged [formula omitted]-type Ti–14Mn–(x)Zr alloys

Low-cost β-type Ti–14Mn–(x)Zr (x = 0, 3, or 6 wt%) alloys were developed and prepared using single-electrode arc furnace, and the effects of the zirconium (Zr) content and thermomechanical treatment on the phase stability, microstructural evolution, hardness, compressive stress, and corrosion resistance of the alloys were studied. The alloy thickness was reduced by approximately 45% by hot forging at 900 °C and were then water quenched and subsequently aged at 500 or 700 °C for different times. The combination of the proper Zr content, hot forging, and aging improved the alloy hardness, strength, and ductility. The dual (α + β) structure formed in the 6Zr alloy forged and then aged at 700 °C for 60 ks resulted in a high compressive yield stress of 1127 MPa and malleability above 70%. The forged and annealed alloys exhibited superior properties to commercial Ti–6Al–4 V (lower cost, corrosion resistance, and mechanical properties). The study findings elucidate the relationship between the composition and processing properties of low-cost Ti–14Mn–(x)Zr alloys for potential biomedical applications.

Investigations on the adhesion and fatigue characteristics of hybrid surface-treated titanium alloy

This study is critical for aiding the development of a hybrid treatment consisting of a tungsten-doped diamond-like carbon coating (WC/C) deposited atop shot-peened Ti-6Al-4V surfaces. Residual stresses, considered a key indicator of fatigue performance, were measured by X-ray diffraction (XRD). Rotating bending fatigue tests were carried out while microscopy allowed for fractographic analysis of resultant surfaces. Results show that despite the pronounced surface roughness produced by the shot peening treatment, the high residual compressive stresses, together with the refined and cold-worked microstructure were capable of marginally improving the fatigue performance of the shot peened Ti-6Al-4V compared to the untreated alloy. Conversely, following fatigue testing, the WC/C coating displayed extensive cracking which propagated prematurely into the substrate and yielded a reduction in fatigue limit. On the other hand, despite some annealing of the compressive residual stresses during the coating deposition treatment, the hybrid treatment yielded a reasonable improvement in the fatigue limit over the untreated condition. This result, coupled with the high coating hardness and adhesion, confirm this hybrid treatment's capability in retaining both the adhesive and fatigue performance of the Ti-6Al-4V alloy.

Friction and wear properties of TiAlN coated tools with different levels of surface integrity

Surface integrity is a critical factor to assess the quality of mechanical products, which has a significant impact on the service performance. In this work, the surface integrity of coating, such as roughness, hardness and residual stress, are changed by micro-blasting. The high-speed sliding wear experiments and cutting experiments are carried out with the TiAlN coated tool with different levels of surface integrity. The influence of the surface integrity of the coating on the high-speed sliding wear and cutting performance is investigated. The result shows that the low surface roughness of the coating can effectively reduce the friction coefficient. The high surface hardness and compressive residual stress (absolute value) can reduce the fluctuation range of friction coefficient. The cutting performance of coated tool is mainly influenced by the surface hardness and surface residual stress. The high wear resistance of the TiAlN coated tool in sliding wear process or cutting process can be obtained at the low surface roughness, the medium hardness and residual stress. It has practical significance to improve the surface integrity and the wear resistance of the coated tools.

Determination of compressive stress in glass-to-metal seals using photoluminescence spectroscopy technique

The stress field and stress evolution of compression seals at micron-scale spatial resolution are experimentally quantified for the first time using photoluminescence spectroscopy (PS) technique. In analyzing the resulting dataset based on fluorescence line shift, it is found that the compressive stress is non-uniform from the center to the periphery of glass, and the highest compressive stress (>300 MPa) is located at the distance of 15∼20 μm to the interface. Further in-situ PS experiments performed at the high compressive stress region reveal that the compressive stress decayed near-linearly with increasing temperature, and instantaneous cracking generated by tensile stress was observed at 320 °C. Moreover, the compressive stress at the interface significantly decayed from 289 MPa to 90 MPa after aged for 800 h at 250 °C. The present work demonstrates an effective method to measure the stress field and sheds light on the future compressive stress tailorability for compression seals.

Injectable, self-healable and adhesive hydrogels using oxidized Succinoglycan/chitosan for pH-responsive drug delivery

We prepared chitosan (CS) based multifunctional hydrogels using oxidized succinoglycan (OSG) with a semi-dissolving acidified sol-gel transition method. OSG cross-linked CS hydrogels (OSG/CS) was prepared by aldehyde-amine Schiff-base reaction. OSG/CS increased not only thermal stability but also improved mechanical strength by 5.75 times. Through the tensile and strain sweep test, OSG/CS showed excellent self-healing properties by 98.82% and 99.89%, respectively. It showed the high compressive stress of 173 kPa at 60% strain, the adhesive strength of 2763 kPa, and the antibacterial effect of 90%. Furthermore, OSG/CS showed a pH-controlled drug release pattern, where a change of pH from 7.4 to 2.0 accelerated for 5-fluorouracil release from 60% to 90%. WST-8 assay demonstrated that OSG/CS maintained 97.30% cell viability and 98.84% cell proliferation after 7 days, indicating the potential as biocompatible hydrogel materials such as wound healing, tissue engineering and drug release systems.

Effects of polishing speed and a water environment on the mechanism of nanometric mechanical polishing of single-crystal lutetium oxide

Molecular dynamics analysis is employed to reveal the atomic-scale details of the material removal process. This method is important to study the nanoscale machining mechanism of nanometric cutting. This article investigates the effects of the polishing speed and a water environment on the polishing force, stress distribution, subsurface deformation, and damage distribution during the nanometric mechanical polishing of the lutetium oxide single crystal using molecular dynamics simulations. The amorphization of material takes place in the region under high compressive stress. The rolling and moving speeds of the abrasive have a combined influence on the distribution of the subsurface damages. A symmetrically distributed amorphous damage layer with a thinner thickness can be achieved when the rolling speed is less than the moving speed. In addition, the polishing speed influences the polishing force, materials removal amount, and subsurface damages significantly. The water environment is conducive to the ductile-mode material removal of the lutetium oxide crystal, increasing the plastic deformation of materials, such as the amorphization, and reducing the brittle damages, such as nanocracks.

Fracturing of shales with slots under uniaxial compression parallel to bedding layers

Shale samples containing single pre-machined slots were tested under uniaxial compression directed along with bedding layers. Observed fractures were initiated by the slots, however, their further development was controlled by the shale bedding layers. Slots normal to the loading direction also cause fracturing and reduce failure load. The fracturing is initiated by tensile stress generated at the slot surface due to convergence of the initial open slot. Therefore, the presence of initial aperture in pre-existing cracks or fractures is capable of changing the mechanism of fracture generation. Three kinds of macroscopic fractures are observed: tensile fractures along bedding layers, shear fractures along the inclined direction, and buckling fractures at the final failure moment. Three types of microcracks are identified: shear microcracks produced from initial weak micro-planes unrelated to the bedding layers, tensile microcracks produced from the shear microcracks in the form of wing cracks, and shear microcracks induced by high uniaxial compression stress. The growth of wing cracks can be assisted by the bedding layers. The research results will contribute to the understanding of failure mechanisms of rocks containing prominent bedding layers.

Напружено-деформований стан проксимального відділу великогомілкової кістки дитини при tibia vara в умовах однобічного блокування проксимальної росткової зони фіксаторами різних типів

Актуальність. Сучасним стандартом хірургічного лікування фронтальних епіметафізарних деформацій колінного суглоба у дітей є метод керованого росту. Для тимчасового блокування росткової зони використовуються різні фіксатори: скоби Блаунта, пластини з гвинтами. Проте дослідження, присвячені вивченню напружено-деформованого стану при використанні зазначених фіксаторів, відсутні.Мета: дослідження напружено-деформованого стану моделі проксимального відділу великогомілкової кістки дитини при однобічному блокуванні росткової зони фіксаторами різних типів в умовах навантажень, характерних для tibia vara.Матеріали і методи. За допомогою програми Solid Works створена і проаналізована методом кінцевих елементів 3D-модель проксимального відділу великогомілкової кістки дитини з латеральним блокуванням одним із 3 фіксаторів: скоба Блаунта, блокована пластина, стандартна пластина в умовах навантаження, характерних для tibia vara.Результати. В умовах навантаження, характерних для tibia vara, відзначено збільшення напружень у медіальній частині росткової зони. При однобічному блокуванні фіксаторами виявлено нові зони підвищених навантажень у кістковій тканині метаепіфіза нижче від росткової зони. Найбільше напруження у фіксаторах відзначено в зоні контакту проксимального гвинта з пластиною, а також у верхній частині скоби.Висновок. Варусна деформація проксимального відділу великогомілкової кістки веде до підвищення навантажень у медіальній частині проксимальної росткової зони. Використання різних фіксаторів для однобічного блокування проксимальної росткової зони великогомілкової кістки призводить до появи відмінних напружень у проксимальному її епіметафізі. До мінімального підвищення напружень у кістковій тканині метафіза приводять варіанти фіксації із застосуванням пластин, а використання скоб Блаунта значно підвищує напруження в кістковій тканині в ділянці розташування скоб.

An indirect approach to measure glass transition temperature in metallic glasses

Abstract Glass transition behavior of metallic glasses under some extraordinary conditions (such as under high pressures) remains unexplored. Conventional measurements of glass transition temperature, T g, are very difficult to perform under these extraordinary circumstances. In the present paper, we introduce an indirect approach to characterize glass transition, using enthalpy recovery experiments. With annealing deeply relaxed glassy samples and subsequent DSC measurements, a variation of enthalpy change upon heating with annealing temperature can be obtained. The variation of enthalpy change, a signature of glass transition, was found to correlate well with the directly measured DSC curves for the glass transition. This unique method was successfully applied in determining T g of several metallic glasses under hydrostatic high pressures and compression stresses.

Thermostability, oxidation, and high-temperature tribological properties of nano-multilayered AlCrSiN/VN coatings

In this study, monolithic AlCrSiN, VN, and nano-multilayered AlCrSiN/VN coatings were deposited using a hybrid deposition system combining arc ion plating and pulsed direct current magnetron sputtering. The microstructure, thermostability, mechanical, oxidation and tribological properties of the coatings were comparably investigated. The multilayered AlCrSiN/VN coating exhibited a face-centered cubic (fcc) structure with (200) preferred orientation and showed the highest hardness (30.7 ± 0.5 GPa) among these three coatings due to the multilayer interface enhancement mechanism and higher compressive stress. The AlCrSiN sublayers effectively prevented the V element from rapid outward diffusion to the surface of AlCrSiN/VN coating at elevated temperatures, which improved the oxidation resistance of the coating. Decomposition of V (Cr)–N bonds occurred at annealing temperatures from 800 °C to 1000 °C and V2N phase appeared at 1100 °C. The AlCrSiN/VN coating showed excellent tribological performance at high temperatures by combining the merits of VN layers for low friction coefficient and AlCrSiN layers for superior oxidation resistance. Compared to VN and AlCrSiN coatings, AlCrSiN/VN coating showed the lowest wear rate of 2.6×10-15 m3/N·m at 600 °C and lowest friction coefficient of 0.26 at 800 °C with a relativity low wear rate of 39.4×10-15 m3/N·m.

Lightweight Nanofibrous Crosslinked Composite Aerogels with Controllable Shapes and Superelasticity for Pressure Sensors

AbstractSo far it is still a big challenge to construct the nanofibrous crosslinked composite aerogels with high compressive stress and excellent elastic resilience for pressure sensors. To solve this problem, a novel strategy of combining rigid inorganic nanofibers and flexible organic nanofibers is designed to obtain the crosslinked composite aerogels with outstanding compressive stress and stability. Surprisingly, the as‐prepared composite aerogels have an extremely low density of 11.27 mg cm−3, and the crosslinked composite aerogels with desire shapes can be easily controlled via changing the different molds on demand. More importantly, the composite aerogels can be compressed up to 80% with a quite high compressive stress of 41 kPa and it can recover to its original state well. It is worth mentioning that the as‐prepared aerogels can be encapsulated to construct ultrasensitive (0.53 kPa−1) and rapidly responsive (315 ms) pressure sensors for encrypted information transmission. Such excellent crosslinked composite aerogels will open up numerous application opportunities for pressure sensors, thermal insulation, and sound absorption.

All-in-One flexible supercapacitor based on hydrogen bonds cross-linked organic gel electrolyte with anti-freezing and anti-pressure properties

Hydrogel electrolytes have gained significant attention in the field of flexible supercapacitors (SCs) for their intrinsic safety, high flexibility, and superior ionic conductivity. However, the water-rich structures of traditional hydrogel electrolytes inevitably cause them to freeze at subfreezing temperatures, which limits the application of flexible supercapacitors at extremely cold temperatures. Here, a compressible and low-temperature resistant supercapacitor is fabricated containing multiple hydrogen bonds cross-linked N-(2-Hydroxyethyl) acrylamide (NHEA), acrylic acid (AA), ethylene glycol/water (EG/H2O), and H2SO4 organic gel electrolyte (OGE). The fabricated OGE exhibits high compressive stress (200 kPa), excellent shape recovery property, and high proton conductivity (62 mS/cm) even at −40 °C. Meanwhile, a reasonable assembly method of All-in-One SCs greatly reduces the contact resistance between the electrode and the gel electrolyte, progressing great capacitance (114 F/g) and flexibility. Remarkably, the device retains high capacitance retention under strong compressive stress (nearly 100%) and long-term circle (90.73% capacitance retention rate after 10,000 cycles). Furthermore, it retains near 76% capacitance at −40 °C, demonstrating the potential for applications in cold climates and high-altitude regions.

Impaired bone quality in the superolateral femoral neck occurs independent of hip geometry and bone mineral density

Skeletal adaptation is substantially influenced by mechanical loads. Osteocytes and their lacuno-canalicular network have been identified as a key player in load sensation and bone quality regulation. In the femoral neck, one of the most common fracture sites, a complex loading pattern with lower habitual loading in the superolateral neck and higher compressive stresses in the inferomedial neck is present. Variations in the femoral neck-shaft angle (NSA), i.e., coxa vara or coxa valga, provide the opportunity to examine the influence of loading patterns on bone quality. We obtained femoral neck specimens of 28 osteoarthritic human subjects with coxa vara, coxa norma and coxa valga during total hip arthroplasty. Bone mineral density (BMD) was assessed preoperatively by dual energy X-ray absorptiometry (DXA). Cortical and trabecular microstructure and three-dimensional osteocyte lacunar characteristics were assessed in the superolateral and inferomedial neck using ex vivo high resolution micro-computed tomography. Additionally, BMD distribution and osteocyte lacunar characteristics were analyzed by quantitative backscattered electron imaging (qBEI). All groups presented thicker inferomedial than superolateral cortices. Furthermore, the superolateral site exhibited a lower osteocyte lacunar density along with lower lacunar sphericity than the inferomedial site, independent of NSA. Importantly, BMD and corresponding T-scores correlated with microstructural parameters at the inferomedial but not superolateral neck. In conclusion, we provide micromorphological evidence for fracture vulnerability of the superolateral neck, which is independent of NSA and BMD. The presented bone qualitative data provide an explanation why DXA may be insufficient to predict a substantial proportion of femoral neck fractures. Statement of significanceThe femoral neck, one of the most common fracture sites, is subject to a complex loading pattern. Site-specific differences (i.e., superolateral vs. inferomedial) in bone quality influence fracture risk, but it is unclear how this relates to hip geometry and bone mineral density (BMD) measurements in vivo. Here, we examine femoral neck specimens using a variety of high-resolution imaging techniques and demonstrate impaired bone quality in the superolateral compared to the inferomedial neck. Specifically, we found impaired cortical and trabecular microarchitecture, mineralization, and osteocyte properties, regardless of neck-shaft angle. Since BMD correlated with bone quality of the inferomedial but not the superolateral neck, our results illustrate why bone densitometry may not predict a substantial proportion of femoral neck fractures.

Determination of the through-thickness residual stress in thick duplex stainless steel welded plate by wavelength-dependent neutron diffraction method

In this study, a wavelength-dependent neutron diffraction method used to measure the residual stress in thick duplex stainless steel (DSS) welded plate was proposed, which was validated by contour method. By choosing appropriate wavelength, the penetration capability of neutron was improved. The neutron with appropriate wavelengths was then applied to investigate the through-thickness volume fraction, macroscopic and phase-specific residual stress in a 55 mm thick DSS welded plate. The results showed that a wavelength at 2.395 Å had more superiorities than the conventionally-used wavelength at 1.593 Å in the measurement of longitudinal and transverse stresses of a thick DSS plate. In general, high tensile stresses were generated in austenite while high compressive stresses were found in ferrite. For elastic mismatch residual stresses, their maximum values in austenite and minimum values in ferrite were located near the mid-thickness region. Reasons for the formation and characteristics of the phase-specific stresses were also discussed. Besides, large tensile macroscopic stresses were found near the surface whilst significant compressive stresses were found to generate in the mid-thickness of weld metal.