Differential Thermal Expansion Research Articles

A method of attaining optical fibre pre-compression for strain and temperature monitoring inside metal at extremely high temperatures

A metal-embedded fibre sensor's highest operational temperature is limited by strain due to differential thermal expansion between fibre material silica and the host metal. For a stainless steel 316 or nickel-embedded fibre sensor, it is approximately 500°C because, above this temperature, thermal strain from the host metal exceeds the tensile strength of the fibre. A novel method of attaining optical fibre sensor pre-compression inside metal for compensating the external thermal strain and achieving strain and temperature monitoring inside metal up to at least 800°C is demonstrated in this paper. The sensor shows good repeatability (error within 10°C) for the twelve temperature cycling experiments carried out after pre-compressing the fibre. Sensor response at different temperatures and external thermal strain shows good long-term stability. The highest operational temperature is limited by the fibre sensing structure (fibre Bragg grating) used in this study; using a distributed sensing interrogator can extend the operational temperature to the limits of optical fibre material with the method demonstrated in this paper.

Investigations on Microstructure, Mechanical, and Wear Properties, with Strengthening Mechanisms of Al6061-CuO Composites

Metal matrix composites (MMCs) reinforced with Copper Oxide (CuO) and Aluminum (Al) 6061 (Al6061) alloys are being studied to determine their mechanical, physical, and dry sliding wear properties. The liquid metallurgical stir casting method with ultrasonication was employed for fabricating Al6061-CuO microparticle-reinforced composite specimens by incorporating 2–6 weight percent (wt.%) CuO particles into the matrix. Physical, mechanical, and dry sliding wear properties were investigated in Al6061-CuO MMCs, adopting ASTM standards. The experimental results show that adding CuO to an Al6061 alloy increases its density by 7.54%, hardness by 45.78%, and tensile strength by 35.02%, reducing percentage elongation by 40.03%. Dry wear measurements on a pin-on-disc apparatus show that Al6061-CuO MMCs outperform the Al6061 alloy in wear resistance. Al6061-CuO MMCs’ strength has been predicted using many strengthening mechanism models and its elastic modulus through several models. The strengthening of Al6061-CuO MMCs is predominantly influenced by thermal mismatch, more so than by Hall–Petch, Orowan strengthening, and load transfer mechanisms. As the CuO content in the composite increases, the strengthening effects due to dislocation interactions between the matrix and reinforcement particles, the coefficient of thermal expansion (CTE) difference, grain refinement, and load transfer consistently improve. The Al6061-CuO MMCs were also examined using an optical microscope (OM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), and scanning electron microscopy (SEM) before and after fracture and wear tests. The investigation shows that an Al6061-CuO composite material with increased CuO reinforcement showed higher mechanical and tribological characteristics.

Realization of Joints of Aluminosilicate Glass and 6061 Aluminum Alloy via Picosecond Laser Welding without Optical Contact.

To achieve laser direct welding of glass and metal without optical contact is hard, owing to the large difference in thermal expansion and thermal conductivity between glass and metal and an insignificant melting area. In this study, the high-power picosecond pulsed laser was selected to successfully weld the aluminosilicate glass/6061 aluminum alloy with a gap of 35 ± 5 μm between glass and metal. The results show that the molten glass and metal diffuse and mix at the interface. No defects such as microcracks or holes are observed in the diffusion mixing zone. Due to the relatively large gap, the glass collapsed after melting and caulking, resulting in an approximately arc-shaped microcrack between modified glass and unmodified glass or weakly modified glass. The shape of the glass modification zone and thermal accumulation are influenced by the single-pulse energy and linear energy density of the picosecond laser during welding, resulting in variations in the number and size of defects and the shape of the glass modification zone. By reasonably tuning the two factors, the shear strength of the joint reaches 15.98 MPa. The diffusion and mixing at the interface and the mechanical interlocking effect of the glass modification zone are the main reasons for achieving a high shear strength of the joint. This study will provide reference and new ideas for the laser transmission welding of glass and metal in the non-optical contact conditions.

Effects of TiB2 contents on the microstructure and oxidation behavior of Mo-Si-B composite coatings

A novel Mo-Si-B-TiB2 composite coating was prepared on Nb-Si based ultrahigh temperature alloy by slurry sintering. The effects of TiB2 contents (1, 3, 5 and 10 wt%) on the microstructure and oxidation behavior of Mo-Si-B composite coatings were revealed. The results show that TiB2 modified Mo-Si-B composite coatings display a bilayer structure, in which the outer layer is composed of MoSi2, Mo5Si3 and TiB2 phases, and the inner layer is composed of (Ti,Nb)5Si4, (Nb,X)5Si3 and (Nb,Ti)B2 phases. The added TiB2 particles are evenly distributed in the outer layer of the coatings. By introducing TiB2 into the coating, the service life of Mo-Si-B composite coatings is extended from 50 h to 100 h at 1250 ℃, the oxidation rate of the coating is reduced from 1.62 to 0.02 mg2 cm−4 h−1. This indicates that the addition of appropriate TiB2 effectively slows down the oxidation rate and significantly improves the oxidation resistance of Mo-Si-B composite coatings. The Mo-Si-B composite coating with 3 wt% TiB2 had the lowest mass gain (3.9 mg/cm2) after oxidation at 1250 ℃ for 100 h, and it exhibited the best oxidation resistance. This is attributed to the formation of composite oxide scale with crack-free, good healing ability, suitable levels of differential thermal expansion and low oxygen permeability.

Cracking failure analysis of potash fertilizer drying drums: Calculations, modeling, experiment

Drying drums are widely used for drying materials in many industries. At the same time, the temperature of the drying gases can exceed 1000 °C, and the materials being dried or the evaporated media can be highly aggressive, which can lead to the destruction of the material of the drying drums. As a result of comprehensive studies, it has been established that the probable causes of cracking of drying drum linings under operating conditions of the drying-granulation department of a potassium ore processing plant are thermal stresses. The research results are confirmed by the results of the analysis of the composition and mechanical properties of the drum material, as well as the calculations performed and modeling results. It has been established that thermal stresses are caused by the difference in linear thermal expansion of the lining and the drum due to significantly different temperature coefficients of linear expansion. The drum and inner lining expand by 18.5 mm and 26 mm, respectively, and the calculated difference is approximately 8 mm. Contact force between the lining and the body of the drying drum reaches 54.44 MN. Maximum stresses experienced by the body of the drying drum do not exceed 6 MPa. The microhardness of austenite grains through which the crack directly passes was ≈150 kg/mm2, and that of unbroken grains was ≈180 kg/mm2. Additionally, cracking of the linings due to thermal stresses is associated with the design features of the drum dryer, expressed in the rigid structure of the lining and drum along the transverse axis. The further development of cracks occurs due to, cyclic thermal effects, and the chlorides enter the cracks.

Towards Implantable Artificial Muscles: Epoxy Based Bilayer Thermal Actuators with Ambient Activation Temperatures

AbstractThe development of soft and biocompatible actuators is a current challenge in the fast‐growing field of soft robotics. A variety of shape‐memory and thermal actuators are currently being explored for application in these areas, especially to produce actuators that can operate at biocompatible temperatures for in vivo applications. Here we detail the synthesis of epoxy based materials, a class of materials not fully explored for soft actuators. By careful tuning of polymer composition by variation of monomer feed ratios, we show tuneable glass transition temperatures (Tgs) of these materials. Ambient temperature (30–60 °C) thermal actuators were then realised by casting of bilayers of epoxy resins with varying Tgs. Differences in thermal expansion when the Tg was reached lead to actuation in a specific direction. With optimisation, actuation in both the external‐heated and joule‐heated NiChrome‐epoxy actuators were able to occur at physiological temperatures (36–40 °C), previously unreported in the literature. For the joule‐heated NiChrome–epoxy actuators surface temperatures remained under 40 °C during actuation at low operating voltages (<2 V). Higher force and power output could be achieved in a repeatable fashion at higher driving voltages without loss of displacement, but also leading to higher surface temperatures. These materials and the actuation approach present an exciting opportunity to develop future implantable actuators to solve significant challenges related to quality of life and an ageing population.

Stress Distribution along the Structural Sealant Joint Length of a Cylindrically Curved Glazing Panel

It has been identified that current standardised method for structural sealant joint dimensioning is applicable to flat rectangular panels only and no provisions are made for panels with curved surfaces. The purpose of this study is to investigate the stress distribution along the sealant joint of a cylindrically curved glass panel subjected to wind pressure and to establish if the panel curvature influences the stress distribution along the joint length. Using numerical method, several curved units were analysed and the results have shown that the out of plane wind action generate compression and shear forces within the joint, both occurring at the same time. This means that in the case of a structurally bonded curved panel, additionally to the shear caused by differential thermal expansion of elements or glass self-wight which is covered by ETAG 002 and EN 13022 the designer must also consider the shear stress induced due to the panel curvature. The magnitude and location of this additional shear stress and also of the tension/compression stress can be identified using Finite Element Analysis.

Changes in the Crystal Lattice Parameters of Bismuth Films on Substrates with Different Thermal Expansion

AbstractDue to the sensitivity of the electronic structure of semi‐metals to small distortions of the crystal lattice, the study of the electrical and galvanomagnetic properties of bismuth films requires taking into account the deformation that occurs in the film‐substrate system due to the difference in the thermal expansion of the film and substrate materials. The magnitude of these deformations plays an important role in analyzing the temperature dependencies of the transport properties of charge carriers. The paper presents an experimental study of the magnitude of deformation of bismuth films on various substrates at 300 and 77 K using X‐ray diffraction. Changes in the lattice constant of crystallites, the trigonal axis of which is perpendicular to the film plane, depending on the substrate material, are obtained. A comparison between the assessment of the deformation of these crystallites in the film plane based on Hooke's law and the difference in the coefficients thermal expansion of the film and substrate materials is made.

Temperature-dependent creep damage mechanism and prediction model of fiber-reinforced phenolic resin composites

Carbon fiber-reinforced phenolic resin (CF/PF) and glass fiber-reinforced phenolic resin (GF/PF) composites are crucial for thermal insulation and load-bearing capabilities in the aerospace industry. Understanding their creep behavior at various temperatures is essential. This study investigates the impact of temperature on the bending creep properties of CF/PF and GF/PF composites, focusing on deformation response, damage mechanisms, and prediction models. Results reveal that the decrease in creep properties at elevated temperatures is mainly attributed to the increased viscoplastic strain. At room temperature, CF/PF composite demonstrates exceptional creep properties. CF/PF composite exhibits heightened sensitivity to elevated temperatures, undergoing creep rupture at 210 °C and 240 °C with failure strains of 0.48 % and 0.49 %, respectively. High-temperature damage mechanisms have been analyzed in depth using a combination of thermal stress finite element simulation and microscopic characterization. Thermal stress is directly related to the difference in thermal expansion between the fibers and the resin. The influence of fiber distribution and geometry results in the interface being subjected to both normal and shear stresses. The accumulation of interfacial damage increases the plastic deformation and degrades creep performance. Additionally, an advanced temperature-dependent Burgers model has been developed and effectively predicted the creep curves under different temperatures and loads. This model demonstrated great potential as a general predictive model.

Research on technological parameters affecting the quality of adhesive joints in casting model assemblies and assessment of their operational properties in liquid and humid environments

Modern casting model kits, often created using adhesive technologies, can experience deformations leading to warping and even destruction. This can occur due to differences in thermal expansion and moisture absorption rates between the material and the adhesive. The study evaluated the behavior of the adhesive joint in model kit elements under operational conditions in liquid and humid environments, assessing the hardness and strength of the joint. The analysis revealed a correlation between the density of the plastic and the quality of the adhesive joint.

Effect of Misalignment at the Flat and Profiled Endwall of Nozzle Guide Vane on Heat Transfer

Misalignment of gas turbine engines is caused by the difference in thermal expansion from the design point when starting or stopping the engine, or when operating at partial load. This study evaluated the differences in heat transfer characteristics between a flat endwall and a profiled endwall with misalignment. To ensure consistency with the flow conditions, experiments were conducted at an outlet Reynolds number of 300,000 for both geometries. The experiment was performed under three different conditions: a case without step, a case with a forward-facing step (h/Cx= -0.1), and a case with a backward-facing step (h/Cx= 0.1). In the flat endwall, the thermal load of the upstream region increases significantly with both step circumstances compared to the case without a step. The misalignment causes a recirculation flow to occur between the interface of the combustor and turbine. This leads to the mainstream reattaching upstream of the endwall. Nevertheless, the heat transfer characteristics of the profiled endwall differ from those of the flat endwall under step conditions. Most locations do not experience significant changes, with only a slight increase observed in the upstream region. The recirculation flow is crucially reduced due to the intensity of the secondary vortex in the profiled shape. Hence, the increase in the thermal load on the profiled endwall with step is considerably lower than that on the flat endwall. As a result, the thermal load on the profiled endwall has decreased by 25 % for the forward-facing step and 20.7 % for the backward-facing step compared to the flat endwall.

Effect of Growth Temperature on Strain during Growth and Crack Suppression in AlGaN Templates on Sapphire Substrates for Deep Ultraviolet Light‐Emitting Diodes

The crack formations in AlGaN templates for deep ultraviolet (DUV) light‐emitting diodes (LEDs) are investigated and successfully suppressed. The strain values in AlGaN thick layers on sapphire substrates by in situ wafer curvature measurements and ex situ X‐ray diffraction measurements are evaluated. It is found that the tensile strain during the AlGaN thick layer growth comes from a thermal expansion difference between the AlGaN thick layer and the sapphire substrate as the temperature changes from the AlN nucleation layer growth to the AlGaN thick layer growth. When the temperature change is 100 °C and less, the tensile strain of 0.1% and less is observed during the AlGaN thick layer growth, resulting in no crack formations in the AlGaN thick layer. Furthermore, a DUV LED layer structure grown on such a crack‐free AlGaN template shows no crack formations. Thus, to suppress crack formation in templates fabricated for DUV LEDs, their growth temperature must be optimized by considering thermal expansions caused by the changes in the growth temperature from the nucleation layer to the thick layer.

Preflight and Postflight Thermal/Structural Analysis of BOLT II: The Holden Mission

BOLT-2: The Holden Mission, a follow-on to the BOLT experiment, was designed to measure the characteristics of turbulent flow in the hypersonic flight regime. This paper summarizes preflight transient thermal and structural analyses for the predicted flight trajectories that led to the selection of suitable materials for the flight experiment. Following the successful flight in March 2022, the preflight analysis methods, along with temperature measurements from the flight, were used to conduct a postflight thermal analysis based on the as-flown trajectory that attempted to match the flight data. Conservatism in the preflight design analysis was compared to the flight measurements. Databases of computed laminar and turbulent heating were generated as part of this effort that can aid in future analysis of the experimental data. The effects of modeling transitional heating during ascent were quantified when compared to a fully turbulent heating assumption. A set of estimated three-dimensional surface temperature distributions have been computed and were found to be a good match to the available flight data. Postflight structural modeling was used to estimate the differential thermal expansion at the nosetip/frustum joint interface.

Role of silicon carbide in enhancing microwave hybrid heating and reducing dewaxing time in investment casting

Mould cracking is a common problem in investment casting (IC) that occurs during the dewaxing process, which is caused by the difference in thermal expansion between the wax pattern and the ceramic mould. Therefore, appropriate modifications to the mould, waxes and hybrid heating of the materials are proposed to address this problem. This study aims to investigate the effects of silicon carbide (SiC) addition on dewaxing time and mould structural defect in two different waxes (HYFILL B289 MOD S and SIVUCH L1203) under microwave hybrid heating. For the mould fabrication, stucco (Al2O3-SiO3) was added with various amounts of SiC to improve microwave heat absorption capabilities. The modified stucco was applied on layers 3–6 to ensure that the mould was more durable and suited for the casting process. The thermal expansion of the waxes and the ceramic mould was evaluated to determine its thermal expansion mismatch. The density, porosity, thermal conductivity, and dielectric properties were characterized to evaluate the properties of modified green mould. The results showed that SIVUCH L1203 wax outperformed HYFILL B289 MOD S wax, in obtaining a crack-free ceramic investment mould with a clean internal surface. This superiority is attributed to the exceptional thermal and absorption properties of the SIVUCH L1203 wax. Furthermore, the incorporation of SiC played a pivotal role in enhancing the hybrid heating process while maintaining the density and porosity of the green moulds. This was evident by the remarkable reduction of dewaxing time by 62% with 7.5% of SiC addition, which also contributed toward improving energy savings and sustainability.

Exploring the role of surface roughness in concrete-based thermal energy storage systems: A computational study

This study computationally investigates the effect of thermal energy storage (TES) material surface roughness on heat transfer fluid (HTF) flow dynamics and heat transfer capabilities. The motivation is to further understand systems where concrete as the TES material directly interfaces with air as the HTF, based on previous research suggesting potential benefits of avoiding differential thermal expansion issues associated with metallic tubes. A k-ε turbulence model in COMSOL Multiphysics examined air flow over concrete surfaces with five levels of roughness from 0 to 3 mm peak height. Increasing surface roughness enhances turbulence and significantly improves heat transfer and thermal storage performance, with 7 % higher charging efficiency and energy storage capacity and 55.6 % greater heat transfer rate from 0.3 to 3 mm roughness, despite a 138 % increase in pressure drop. Applying artificial surface modifications like indentations or fins could further optimize efficiency by amplifying heat transfer advantages of increased roughness while moderating pressure losses. This indicates a promising direction for future research on enhancing thermal energy storage through concrete surface optimization and substantiates the potential of concrete as an inexpensive, scalable, high performance TES material.

Advancing additive manufacturing: 3D‐printing of hybrid natural fiber sandwich (Nona/Soy‐PLA) composites through filament extrusion and its effect on thermomechanical properties

AbstractThe additive manufacturing technique represents a technological advancement post the industrial revolution, enabling the development of intricate products with minimal waste. In the automotive sector, polymer extrusion‐based additive manufacturing is predominantly employed for part customization. Recently, reinforced polymer matrices have been used to enhance structural integrity, primarily utilizing synthetic materials. Due to environmental concerns, some recent studies have explored the incorporation of natural fiber reinforcement in polymer matrices for 3D‐printed products. Most research has focused on filler reinforcement, limiting investigations to a single type of reinforcement. To bridge this gap and enhance composite performance, our research introduces a novel method for 3D printing composites. This involves stacking sequences using two different natural fiber‐reinforced polylactic acid (PLA) filaments, namely Nona and Soy, respectively. Mechanical testing reveals that the stacking sequence significantly influences the mechanical properties of the 3D‐printed composites. The 3D‐printed composite with Soy/PLA skin stacks exhibits the highest tensile strength of 74.82 MPa. Thermal analysis shows minor changes in glass transition temperature (Tg) and a consistent degree of crystallinity (10.01%). Notable differences in thermal expansion are observed due to the stacking sequence. Fatigue analysis demonstrates the durability of hybrid composites, enduring over 42,000 cycles with minimal deformation compared with to pure fiber‐reinforced 3D‐printed composites. Morphological analysis reveals excellent fiber–matrix interaction and bonding between stacks. The observations confirm that the developed material can be potentially used for developing structurally enhanced composites for lightweight applications. Moreover, the proposed methodology can be adapted for different 3D printing matrices, including robotic printing with multiple axes, making it suitable for various industrial sectors.Highlights Utilization of 3D printing technology for the development of agro‐waste fiber products. Hybridizing the 3D‐printed composite enhanced the fatigue life. New additive manufacturing technique for developing structurally enhanced composites.

Analysis of the ceramic coatings' recrystallization produced on the surface of the Zr-25Ta-25Ti alloy

The objective of this study is to analyze the influence of the heat treatment temperature carried out at ultra-high vacuum on surfaces formed in the Zr-25Ta-25Ti alloy by the micro-arc oxidation (MAO) technique to produce a ceramic layer with high hardness and high wear resistance. The results of structural (XRD) and microstructural characterization (SEM, optical and confocal microscopy technique) show that the surfaces are mainly composed of zirconium dioxide (ZrO2), Ti2ZrO, and calcium oxide (CaO). The heat treatments at high temperatures (500–800 °C) altered the phases of the MAO coating, forming ZrC. Confocal images showed that increasing temperature increased the roughness of the coatings (0.65 → 1.06 μm). Consequently, the topography of the coatings, wettability, microhardness (Vickers), and wear resistance (obtained by the ball cratering technique) of the materials are also modified. The wear results show that the MAO coating has a low wear rate value due to the MAO surfaces’ high hardness, efficiently protecting the substrates of the Zr-25Ta-25Ti alloy against tribological phenomena. Finally, the increase in heat treatment temperature promoted the formation of cracks in the coatings due to the difference in thermal expansion of the MAO ceramic with the Zr-25Ta-25Ti alloy substrate, causing a decrease in the hardness value and reducing wear resistance.

Microstructural evaluation and mechanical properties of WC-6%Co/AISI 1045 steel joints brazed by copper, brass, and Ag-based filler metals: Selection of the filler material

Due to the higher production cost of the monolithic carbide tools as well as their brittle nature, cemented carbides such as WC-Co are frequently joined to tool steel. To overcome the joining complications that arise due to notable differences in thermal expansions between the components and the poor wettability, various investigators have used copper-based and silver-based filler metals to dissimilarly braze the cemented carbides to steels. However, researchers do not agree about the selection of filler material. This research investigates the use of pure copper, brass, and silver-based filler metals to join the WC-Co cemented carbide to AISI 1045 steel. In this regard, microstructural features and mechanical properties including microhardness and shear strength were studied. The results indicate the formation of Cu(Fe,Co) solid solution and η carbides at the joint interfaces as well as the development of various precipitated phases in the joint area comprising Fe-Zn and Co-Zn intermetallic compounds. The reaction layers at both sides of the joints accompanied by cobalt-depleted zone on the hard metal side were observed. While using the α−β brass interlayer, the increase in hardness of the joint area through the presence of (Cu,Zn) solid solution compared to pure copper, the joint shear strength was enhanced from 161 to 173 MPa. On the other hand, the utilization of silver-based filler alloy with a distribution of hard copper-rich solid solution phase (182 HV) embedded in a silver-rich ductile matrix (88 HV), presenting a dispersion hardening effect, improved the shear strength of the joint to 203 MPa.

Development of Printed Circuit Boards with High Thermal Conductivity and Low Thermal Expansion by Applying Cu-Mo Composite Materials

In recent years, electronic devices are strongly required to be smaller, lighter, and more powerful. As a result, mounted components have become smaller, more powerful, and denser, and the heat generation density on printed circuit boards (PCBs) has increased. Since rising component temperatures can lead to component failure, efficient heat removal from the generated heat has become an urgent issue. Since general PCBs have low thermal conductivity, when high heat dissipation is required, methods to increase the thermal conductivity of PCBs have been employed by increasing the copper (Cu) content in the PCB or by placing an aluminum (Al) alloy in the inner layer. However, while Cu and Al have high thermal conductivity, they also have high coefficients of thermal expansion (CTE) and young’s modulus, and the CTE of a PCB with increased thermal conductivity using these materials is high. If the thermal expansion difference between the PCB and mounted components is large, reliability against heat cycles cannot be obtained. Therefore, we have focused on copper-molybdenum (CuMo) composite materials with high thermal conductivity, high elastic modulus, and low thermal expansion. We have been utilizing Cu-Mo for the development of our PCBs and fabricated multilayered CuMo composite PCBs; therefore, this report will focus on the results regarding thermal characterization of prototype PCBs.

Strain modulation of epitaxial h-BN on sapphire: the role of wrinkle formation for large-area two-dimensional materials.

Strain built-in electronic and optoelectronic devices can influence their properties and lifetime. This effect is particularly significant at the interface between two-dimensional materials and substrates. One such material is epitaxial hexagonal boron nitride (h-BN), which is grown at temperatures often exceeding 1000 °C. Due to the high growth temperature, h-BN based devices operating at room temperature can be strongly affected by strain generated during cooling due to the differences in lattice thermal expansion of h-BN and the substrate. Here, we present results of temperature-dependent Raman studies of the in-plane E2ghighphonon mode in the temperature range of 300-1100 K measured for h-BN grown by metalorganic vapor phase epitaxy. We observe a change, by an order of magnitude, in the rate of the temperature-induced frequency shift for temperatures below 900 K, indicating a strong reduction of the effective h-BN/substrate interaction. We attribute this behavior to the creation of h-BN wrinkles which results in strain relaxation. This interpretation is supported by the observation that no change of layer/substrate interaction and no wrinkles are observed for delaminated h-BN films transferred onto silicon. Our findings demonstrate that wrinkle formation is an inherent process for two-dimensional materials on foreign substrates that has to be understood to allow for the successful engineering of devices based on epitaxially grown van der Waals heterostructures.