Thermal Expansion Tests Research Articles

Characterization of mechanical and temperature effects on delamination and basic strength behaviors of PVC coated PUR foam substrate used in bus dashboard

This study focuses on the delamination and characterization of different loadings and temperature conditions of polyvinyl chloride (PVC)-coated polyurethane (PUR) foam component layers commonly used in bus dashboards. The method was developed through mechanical and thermal tests.The study involves the examination of primer and no primer PVC-coated PUR components using SEM (Scanning Electron Microscope), tensile-compression, three-point bending, primer characterization, peel, PUR material thermal expansion, and thermal tests. Physical and material tests were conducted to determine the mechanical properties of PVC and PUR foam and the material properties of the primer. Fourier transform infrared spectroscopy (FTIR) analysis was also conducted to identify the functional groups present in the PVC, PUR, and primer materials, helping to understand the material interactions.Some tests produced the expected results, while others did not. The primer characterization and three-point bending tests were unsuccessful due to sample foam breakage. However, tensile-compression tests, peel tests, thermal expansion tests, and thermal tests yielded the desired outcomes. During thermal testing of primed samples, it was observed that the samples shortened and bent as the primer material melted and began to separate from the PVC and PUR layers. This bending and swelling were attributed to the difference in thermal expansion coefficients between the melting primer material and the PVC and PUR layers. The results demonstrate that PVC-coated PUR components can be effectively separated, and they also highlight opportunities for design modifications to improve the durability of bus dashboards.

Effect of stannous oxide on the structure and properties of iron phosphate glass

A novel phosphate glass of the P2O5-SnCl2-Fe2O3 system was synthesized using the melt-cooling technique. The effect of substituting SnO for SnCl2 on the properties of the glass was systematically explored. The material was analyzed using X-ray diffraction (XRD), differential scanning calorimetry (DSC), Fourier-transform infrared spectroscopy (FTIR), and a thermal expansion test. The thermal expansion coefficient (TEC) analysis revealed that the glass transition temperature initially rises and subsequently falls with increasing SnO content. The incorporation of Sn and Fe ions not only reduces the characteristic temperature of the glass but also enhances its chemical stability, presenting significant potential for applications in low-temperature sealing technologies.

Analysis of the destruction of a die insert used in the industrial process of hot die forging to produce a yoke forging

The article performs an analysis of the destruction of forging dies (with two impressions for a double system) used in the industrial process of forging on a hydraulic hammer to produce a yoke forging with a complex geometry. A detailed analysis was performer on one of the lower dies made of non-standard hot chromium-molybdenum-vanadium tool steel, selected for the tests due to its premature damage (a crack) and relatively low durability equalling only 1200 forgings, that is 600 forged elements. Based on the performed complex studies (surface scanning, microhardness tests, microscopic tests, numerical modelling, impact strength trials) it was demonstrated that the most dangerous destruction mechanism for the analyzed process is mechanical cracking and thermo-mechanical fatigue. As a result of the tool working under extreme conditions (high cyclic mechanical impact loads as well as thermal loads), the most intensive damage of the roughing pass, caused by thermal fatigue and abrasive wear, takes place in the areas of complex geometry as well as intensive flow of the forging material on the radii of the roundings. In turn, in the case of the finishing pass, we observe mechanical fatigue cracking of the tool in the areas of stress and high pressure concentration. The results of FEM modelling combined with the results of a microstructural analysis made it possible to determine the causes of the formation of cracks in the working area of the die, which included cyclic high thermal and mechanical loads as well as abrasive wear as a result of intensive flow of the forging material. Within the conducted studies, directions of further investigations were also proposed in order to improve the durability of the examined tool. Additionally, the observed high tendency of the tool material to crack, based on thermal expansion and impact tests and the determination of the crack resistance coefficient K1C, led to the proposal of an alternative material with higher impact strength.

Effect of Annealing Temperature on Microstructure and Properties of DH Steel and Optimization of Hole Expansion Property

In this article, DH steel containing Nb and Nb-Cu above 1000 MPa was designed, and its phase transformation law was analyzed through thermal expansion tests. The influence of annealing temperature on the microstructure and properties of DH steel was studied using a continuous annealing simulation testing machine, SEM, and tensile testing machine. The results showed that under a continuous annealing process, the test steel is composed of ferrite, martensite, a small amount of bainite, and residual austenite. The tensile strength decreases with the increase in annealing temperature, Cu element is dissolved in the matrix which produces solid solution strengthening and results in an increase in the strength of Cu-bearing test steel. Finally, 1180 MPa grade DH steel with excellent comprehensive properties was obtained at an annealing temperature of 840 °C and an overaging temperature of 340 °C. The expansion performance of the experimental steel was studied and optimized. Under the step heating annealing process, the experimental steel is composed of tempered martensite, ferrite, and residual austenite, with smaller differences in hardness between different phases, lower average dislocation density, and better expansion performance. Cu-bearing DH steel achieved an excellent match of strength and plasticity of 1289 MPa × 19.8%, with the hole expansion rate of 21.9% and the loss rate of hole expansion rate of 10%.

Physicomechanical, Wettability, Corrosion, Thermal, and Microstructural Morphology Characteristics of Carbonized and Uncarbonized Bagasse Ash Waste-Reinforced Al-0.45Mg-0.35Fe-0.25Si-Based Composites: Fabrications and Characterizations.

An effort was being made to incorporate waste bagasse ash (WBA) both in carbonized and uncarbonized form into the formulation of Al6063 matrix-based metal matrix composites (MMC's) by partially substituting ceramic particles for them. In the process of developing composites, comparative research on carbonized WBA and uncarbonized bagasse powder was carried out in the role of reinforcement. Microstructure investigations revealed that carbonized WBA particles were properly distributed throughout the aluminum-base metal matrix alloy. They also had the appropriate level of wettability. The reinforcement of carbonized WBA particles in AA6063-based matrix material had a maximum tensile strength of 110 MPa and a maximal hardness of 39 BHN when 3.75 wt % of the particles were used. The deterioration in tensile strength (6.25 wt % of WBA) and the appearance of porosity and blowholes can be enumerated by tensile fractography-based scanning electron microscopy (SEM) analysis. The reinforcement of carbonized WBA particles in AA6063-based matrix material was found to have a maximal percent elongation of 14.42% and the highest fracture toughness of 15 Joules when 1.25 wt % of the particles were employed. For AA6063/3.75 wt % carbonized WBA-based MMC's, the minimum percent porosity was determined to be 5.83, and the minimum thermal expansion was found to be 45 mm3. As the percentage of reinforcement in bagasse-reinforced composites increases, the density of the material, the amount of corrosion loss, and the cost all decrease gradually. The AA6063 matrix, with a composition of 3.75 wt % carbonized WBA-based MMC's, had satisfactory specific strength and corrosion loss. The AA6063 alloy composite's microstructure analysis revealed that carbonized WBA enhanced the material's mechanical characteristics, contributing to its excellent mechanical capabilities. The results of the corrosion test showed that carbonized WBA-reinforced composites exhibited reduced weight loss due to corrosion, whereas uncarbonized bagasse powder was an inappropriate reinforcement. The SEM analysis of AA6063 alloy/3.75 wt % carbonized WBA ash reinforcement-based MMC's exposed to a 3.5 wt % NaCl solution has exhibited the development of corrosion pits as a result of localized attack by the corrosive environment. The thermal expansion test showed that the composite with uncarbonized bagasse powder as reinforcement have a high shrinkage rate in comparison with the composite with 3.75 wt %. The composite's mechanical characteristics and thermal stability were enhanced by the presence of hard phases like SiO2, Al2O3, Fe2O3, CaO, and MgO, as revealed by X-ray diffraction analysis. This made it suitable for use in a variety of applications.

Effect of Starch Content on Morphology, Mechanical Properties, and Thermal Properties of Mullite-Based Porous Ceramic as a Candidate Filter in Aluminum Casting

Research on ceramic filters, needed in the aluminum casting industry because of their ability to filter inclusions, has been done. This study's primary material to make ceramic or local filters is kaolin. The manufacture of local filters in this study uses the dry press method. In this study, potato starch with a composition of 5%, 10%, and 15% acted as a pore-former in the local filter. The local filter burned to a temperature of about 1200°C to obtain the mullite phase. Local filter characterization used SEM, XRD, XRF, and DTA. Several tests were carried out in this study, including Permanent Linear Change (PLC) test, thermal expansion test, flexural strength test, and porosity test. The results obtained in this study show that pores on the local filter are not open, have a prolate shape, and have an average pore size of 10 to 55 m. Burning kaolin up to 1200°C proved successful in obtaining the mullite phase. Another result of this study, the more starch content added to the material, the greater the shrinkage and expansion of the material; the highest shrinkage value on the material is 0.17%, and the highest expansion value of the material is 0,29%, the 15% values owned by potato starch. It is different in the flexural strength value, which has the highest value with 0% potato starch at 14.14 MPa and the lowest value with 15% potato starch at 5.39 MPa.

The characterization of low-k thin films and their fracture analysis in a WLCSP device

The IC industry implements low dielectric constant (low-k) materials in copper/low-k interconnects to reduce the RC delay and crosstalk noises. As low-k dielectrics are weaker than traditional SiO2, measuring their mechanical properties is important for numerical simulations to evaluate the structural integrity of a package with low-k materials. In this study, we fabricated freestanding samples of low-k thin film with/without pre-cracks on both sides using lithography and exfoliation for uniaxial tension and coefficient of thermal expansion tests. The tension tests revealed that the average fracture toughness and Young's modulus of the low-k film are 1.41 MPa·m1/2 and ∼2.5 GPa, respectively. Using the measured mechanical properties, we performed a fracture analysis by a 2D finite element model for the low-k material in a wafer-level chip-size package under thermal loading. The computational results showed that the critical microcrack in the low-k layer occurs near the solder balls, where the KI increases rapidly with crack length and exceeds KIC. The results are consistent with the experimental findings in literature. The present methods can help evaluate the integrity of low-k material in a package and improve reliability.

Regulating the binder phase of polycrystalline diamond compact by adding tantalum to enhance the mechanical properties

In this study, PDC added with tantalum was successfully prepared via high pressure and high temperature (HPHT, 7.7GPa and 1650 °C) with the Cubic-Anvil Press. The effect of tantalum on the mechanical properties and thermal stability was systematically investigated by hardness, abrasion resistance, impact resistance and coefficient of thermal expansion (CTE) tests. The results showed that the hardness, wear ratio, total impact energy and initial expansion temperature increased by 21.7%, 45.5%, 55.2% and 20 °C with the addition of tantalum, respectively. The Ta-PDC material binder phase consisted of Ta-phases (TaC, (Ta,W)CX) and cobalt phase after sintering. In elemental quantification observe that the addition of Ta facilitated cobalt infiltration which was benefit to diamond-diamond bonding. The improvement of mechanical properties and thermal stability can be attributed to the reinforced binder, refined and deagglomerated WC grains at the interface between PCD layer and substrate, and better sintering quality. Further optimization of the Ta additive phase content, mixing methodology, or sintering conditions could be explored to further improve the mechanical properties and thermal stability of this novel PDC material.

Thermal Expansion and Adsorption Characteristics of Coal Based on Temperature Change and Its Influence on the Slippage Effect

The slippage effect is an important phenomenon of coalbed methane (CBM) migration. As the exploitation of CBM, the slippage effect becomes more and more obvious. For exploring the evolution of the slippage effect as CBM extraction by heat injection, the thermal expansion test and the temperature increasing desorption test under different stress states, as well as the seepage test under variable temperature conditions, were conducted by operating the high-temperature multifunctional triaxial test system. The effect rules for temperature and pore pressure on the slippage effect were analyzed, and then the evolution mechanism of the slippage factor at the united action of pore pressure and temperature was comprehensively analyzed based on thermal expansion deformation and adsorption characteristics. The results showed that: first, the influence of pore pressure on the slippage effect is mainly caused by the molecular mean free path and effective stress when pore pressure is greater than 0.8 MPa in the range of 30–150 °C. With the pore pressure increase, the slippage effect decreases. Second, the temperature influence on the slippage effect is mostly induced by the variation of cracks in coal due to thermal expansion deformation created by temperature. With the increase in temperature, the slippage factor average increases first from 30 to 60 °C is 19 times and then decreases from 60 to 90 °C is 36%. Finally, at the combined influence of temperature and pore pressure, the slippage effect is mainly influenced by thermal expansion deformation, desorption deformation, and effective stress. At 30–60 °C, the slippage factor is principally affected by thermal expansion deformation. At 60–90 °C, the slippage factor is mostly influenced by desorption deformation and effective stress. The research results provide a foundation for the technology of CBM exploitation by heat injection.

Effect of CaF2 and Na2SiF6 nucleating agents on the crystallization behavior and properties of MgO-Al2O3-SiO2 glass-ceramics

MgO-Al2O3-SiO2 (MAS) glass-ceramics were prepared by melt and sintering method, and the effects of two kinds of nucleating agents CaF2 (labeled as C-group) and Na2SiF6 (labeled as N-group) on the crystallization kinetics mechanism, crystallization behavior, physical and chemical properties of MAS glass-ceramics were investigated. Herein, differential scanning calorimetry (DSC), X-ray diffraction (XRD), Field-emission scanning electron microscopy (FESEM), density, corrosion resistance, dielectric properties, coefficient of thermal expansion (CTE) and other tests were carried out to evaluate the performance of both parent glass and glass-ceramics samples. The results show that the nucleating agent of CaF2 and Na2SiF6 exhibit a significant influence on the characteristic temperatures of Tg and Tp, and crystallization kinetics of MAS parent glass. The Tg of C-group parent glass are slightly higher than that of N-group parent glass. The Avrami parameter n value for N-group and C-group parent glass are 3.8 and 2.5, which suggesting the main crystal phase in N-group and C-group parent glass present three-dimensional and two-dimensional growth, respectively. However, the nucleating agent of CaF2 and Na2SiF6 present a negligible influence on the crystallization behavior, bulk density, acid resistance, CTE, dielectric constant and dielectric loss of MAS glass-ceramics. When the crystallization temperature increased from 900 to 1000 °C, the main crystal phase precipitated from the all these MAS glass-ceramics kept unchanged with α-cordierite phase (Mg2Al4Si5O18), and the grain size of these rod-like α-cordierite phase around 300–500 nm. All these two groups MAS glass-ceramics present low relative dielectric constant (εr), which is ranges from 1.32 to 2.40, and the εr of C-group glass-ceramics increases with increasing of the crystallization temperature. The MAS glass-ceramics samples also display low dielectric loss (tan δ), which is ranges from 0.42 × 10−2 to 4.93 × 10−2. This finding suggests the MAS glass-ceramics would be used as a potential candidate of dielectric materials for electronic devices, especially for high frequency applications.

Effects of post-treatment on metal-ceramic bond properties of selective laser melted Co-Cr dental alloy. Part 1: Annealing temperature

Statement of problemDental cobalt-chromium (Co-Cr) alloy manufactured by selective laser melting (SLM) is not recommended for clinical applications before annealing because of excessive residual stress. However, limited information is available regarding the relationship between annealing temperature and the metal-ceramic bond properties of SLM Co-Cr alloys. PurposeThe purpose of this in vitro study was to investigate the effects of annealing temperature on the metal-ceramic bond properties of SLM Co-Cr alloys. Material and methodsFour groups with different annealing temperatures (850 °C; 950 °C; 1050 °C; 1150 °C) were prepared by using SLM techniques. Bond strengths were measured by using a 3-point bend test; subsequently, debonded surface morphologies and elements were assessed by using a scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS). The area fraction of adherence porcelain (AFAP) value was introduced to analyze fracture characteristics. Microstructural and interfacial characteristics were characterized by SEM/EDS and X-ray diffraction analysis. The coefficient of thermal expansion (CTE) test was used to analyze thermal matching. A 1-way ANOVA and the Tukey honestly significant difference tests were used to analyze bond strengths and AFAP values statistically (α=.05). ResultsThe mean ±standard deviation values of the metal-ceramic bond strengths were 40.68 ±4.34 MPa for the 850 °C group, 37.54 ±5.34 MPa for the 950 °C group, 45.97 ±2.18 MPa for the 1050 °C group, and 50.79 ±1.79 MPa for the 1150 °C group. Significant differences (P<.05) were observed among all groups. Debonded surfaces and AFAP analysis displayed a mixed fracture mode of adhesive and cohesive fracture, and 1150 °C-annealing specimens exhibited better fracture characteristics close to cohesive fractures. As the temperature increased, native oxide film thicknesses remained unchanged; the 850 °C group had the thinnest diffusion layer, while the other 3 groups had similar thicknesses. Although the 1050 °C and 1150 °C groups displayed higher CTE values, their microstructures were more conducive to atomic diffusion and improved chemical bonding. Microstructure analysis found that ε phase and second-phase precipitates jointly affected metal-ceramic bond strength. ConclusionsAnnealing temperatures affected the metal-ceramic bond strengths of SLM Co-Cr porcelain specimens. 1150 °C annealing SLM Co-Cr specimens displayed higher bond strengths and improved fracture and interface characteristics among the 4 groups.

Embedded-based Thermal Expansion Meter Test System Design

In order to realize the intelligent test of thermal expansion, the overall design scheme of the thermal expansion test system is given, the test platform of the thermal expansion test system is constructed, and the single-neuron PID control algorithm is used to control the heating rate of the electric furnace by using the microcontroller, the upper computer software is written by using Python, the data transmission between the upper computer and the microcontroller is made through the software, and the real-time acquisition of temperature and displacement signals is realized. The software enables data transfer between the upper computer and the microcontroller, real-time acquisition, storage, and analysis of temperature and displacement signals, and it is able to meet the requirements of practical engineering tests.

Preparation and Electrochemical Properties of Cathode Materials Ln2-x Y x CuO4+δ for Solid Oxide Fuel Cell.

Ln2-x Y x CuO4+δ (Ln = Pr, Nd, Sm; x = 0, 0.025, 0.05, 0.1) cathode materials were synthesized using a sol-gel method and calcination at 1000 °C for 24 h. The phase structure, coefficient of thermal expansion (CTE), electrical conductivity, and electrochemical impedance of cathode materials were characterized. X-ray diffraction (XRD) patterns show that the cell volume of each cathode material decreases with the increase in the Y3+ doping amount and has good chemical compatibility with the Sm0.2Ce0.8O1.9 electrolyte. The thermal expansion test shows that the increase in Y3+ doping reduces the average CTE of Ln2CuO4+δ. The conductivity test shows that Y3+ doping increases the conductivity of Ln2CuO4+δ, and Pr1.975Y0.025CuO4+δ has the highest conductivity of 256 S·cm-1 at 800 °C. The AC impedance test shows that Y3+ doping reduces the polarization impedance of Ln2CuO4+δ, and Pr1.9Y0.1CuO4+δ has a minimum area-specific resistance (ASR) of 0.204 Ω·cm2 at 800 °C. In conclusion, Pr1.975Y0.025CuO4+δ has the best performance and is more suitable as a cathode material for a solid oxide fuel cell (SOFC).

High speed ultraviolet digital image correlation (UV-DIC) for dynamic strains at extreme temperatures.

Digital Image Correlation (DIC) is a camera-based method of measuring full-field displacements and strains from the surface of a deforming object. It can be applied at any length scale (determined by the lenses) and any time scale (determined by the camera), and because it is non-contacting, it can also be used at temperatures much higher than can be withstood by bonded strain gauges. At extreme temperatures, materials emit light in the form of blackbody radiation, which can saturate the camera sensor. It has previously been shown that the emitted light can be effectively screened by using ultraviolet (UV) cameras, lenses, and filters; however, commercially available UV cameras are relatively slow, which limits the speed of combined UV-DIC measurements. In this study, a UV intensifier was paired with a high-speed camera, and its ability to perform UV-DIC at high temperature and high speed was investigated. The system was compared over three different experiments: (A) a quasi-static thermal expansion test at high temperature, (B) a vibration test at room temperature, and (C) the same vibration test repeated at high temperature. The system successfully performed DIC up to at least 1600 °C at frame rates of 5000fps, which is more than 100 times faster than other examples of UV-DIC in the literature. In all cases, measurements made using the UV intensifier were much noisier than those made without the intensifier, but the intensifier enabled measurements at temperatures well above those which an unfiltered high-speed camera otherwise saturates.

The investigation of SrCoO3-δ perovskite doping cobalt oxide thermochemical energy storage system

BackgroundThe current research of doping for metal oxide thermochemical energy storage (TCES) systems mainly focuses on the mutual doping among traditional metal oxides. However, it is too one-sided to solve the problem. In this work, SrCoO3-δ perovskite material is novelly doped into the cobalt oxide material system to solve the dehiscent problem of honeycombs, while compensating the energy storage density of materials system. MethodsSimultaneous thermal analysis (STA) is used to assess energy storage density, reaction kinetics, stability of materials. Thermo-mechanical stability assessment and thermal expansion tests are conducted to analyze the anti-crack performance of honeycombs. XRD, SEM, and XPS methods are used to analyze the characteristics of materials. Significant findingsThe mass ratio of doping of 30% exhibits the best comprehensive performance. Based on this, the attenuation of energy storage density of SrCoO3-δ doping is narrowed from 27.1% to 22.9% at least compared with Al2O3 doping for anti-crack, and SrCoO3-δ doping has no negative effects on reaction kinetics of original cobalt oxide and a better stability. Beyond that, the SrCoO3-δ doping method of this work exhibits a better balance among various performance indicators of TCES than traditional doping methods based on improving TCES performance.

Numerical and Experimental Investigation of the Effects of Thermal Expansion and Pressure Loss in Air Hoses made from Different Materials

This study was carried out to numerically and experimentally examine the thermal expansion of four different air hoses with the same geometric shape and dimensions, produced from rubber types with different raw materials, and to examine its effects on pressure loss. Hoses are manufactured from EPDM, ECO, AEM and NBR/CSM rubber compounds. The thermal expansion test was performed at 100°C and 140°C. Thermal and flow analyses and solid-fluid interaction (FSI) analyzes were performed with ANSYS 19.2 commercial finite volumes software. In the study, independence from mesh number was studied. k- Ɛ was chosen as the turbulence model. As a result of the study, the maximum expansion was observed in ECO material and in AEM, EPDM and NBR/CS materials, respectively. It has been determined by tests and analyses that air hoses made of AEM and ECO materials with a low modulus of elasticity have the highest values in diameter expansion. These deformation values caused the pressure value of 300 kPa to decrease to 298.5 kPa at 100 oC and to 298.41 kPa at 140 oC for AEM and decreased the 300 kPa pressure value to 298.1 kPa for ECO. It has been determined that the importance of material selection in air hose designs and the deformation due to the material will affect the pressure loss

Thermal stress analysis and structural optimization of ladle nozzle based on finite element simulation

The ladle nozzle is one of the most important components in metal smelting. The cracking phenomenon occurs due to excessive thermal stress, which seriously affects the performance and life of the ladle nozzle. In this paper, a new composite structure of ladle nozzle is proposed, which consists of two materials with different properties and costs. The thermal physical parameters of the material are measured by high temperature dynamic Young’s modulus test method, thermal expansion test and flashing method. Based on the new structural model of the composite ladle nozzle, finite element simulation is used to combine the material ontology model, contact mechanics model and heat transfer model to study the temperature and thermal stress distribution inside the composite structure of the ladle nozzle during the casting process by taking representative key points inside the ladle nozzle. There is a large temperature gradient in the area near the casting hole, and the farther away from the casting hole, the smaller the temperature change. The ladle nozzle structure was optimized and compared with the existing ladle nozzle structure. The results show that the optimized composite structure of the ladle nozzle has significantly lowered thermal stress extremes under thermal shock, while the thermal stress distribution tends to be more uniform, which can largely reduce the chance of crack generation. This study is of great significance for improving the reliability and service life of the ladle nozzle and reducing its production cost.

Phase transformation and microstructure evolution of Ti6Al4V-0.55Fe alloy with different initial microstructure during continuous heating

The phase transformation during continuous heating of Ti6Al4V-0.55Fe alloy with various initial microstructure including equiaxed, duplex and lamellar microstructures was investigated by thermal expansion test. The results illuminate that the β→α phase transition curves of the three samples all present the sigmoidal “S" shape, which proves that this process is controlled by nucleation and growth. The activation energies and Avrami indexes of phase transformation were obtained by Kissinger-Achaia-Sunose (KAS) method and Kolmogorov-Johnson-Mehl-Avrami (KJMA) model. The average activation energies of the phase transitions in the three samples with initial equiaxed, duplex and lamellar microstructures are 163.9, 194.4 and 231.5 kJ/mol, respectively. The result implies that the phase transition is more likely to occur in equiaxed microstructure, which is consistent with the results of sigmoidal “S" shaped curves. Besides, the phase transition mechanism of samples with different initial microstructures presents three different stages, including nucleation and diffusion of crystals, diffusion phase transition, and meaningless numerical interval. Furthermore, the microstructure evolutions of the three samples were analyzed by thermal expansion method at a heating rate of 5 K·min−1. The phase transformation is divided into three stages: lamellar α mainly merges into thicker α phase, thick α transforms into β phase and finally equiaxed α transforms into β phase. The layered α occurs obvious coarsening first and then redissolution phenomena during the α phase transition. The difference in the morphology, size and composition of layered α and primary equiaxed α can affect the phase transformation behavior of the alloy during the heating process.

Thermal properties of amino-functionalized multi-walled carbon nanotubes reinforced epoxy-based transducers embedded in concrete

Aiming to improve the thermal properties of ultrasonic transducers used in concrete structure, a novel amino-functionalized multi-walled carbon nanotubes (MWCNTs) reinforced epoxy/cement composite was designed to prepare the packaging layer of ultrasonic transducers. Thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), thermal conductivity test, and thermal expansion test were conducted to investigate the effects of different amounts of amino-functionalized MWCNTs (amino-MWCNTs) on the thermal properties of the transducer packaging materials. The results showed that, the optimal thermal properties of the ternary composite are achieved when the amino-MWCNT content of epoxy matrix is 1.25 wt%. Compared with the epoxy/cement binary composite, the thermal conductivity of the ternary composite with the optimal content of amino-MWCNTs at 25 °C increased by 116.3%, and the expansion ratio at 60 °C reduced by 51.6%. The improvement of thermal properties of the ternary composite is benefit from the homogeneous dispersion of amino-MWCNTs in the matrix. The addition of amino-MWCNTs in the transducer is proved to improve the thermal properties of the embedded transducer packaging layer in concrete structure under the action of alternate wetting and drying thermal cycles.

Fracture forms and multiple undulated morphology of polycarbonate LTW by introducing carbon black coated copper film

In the process of laser transmission welding (LTW) polymer with metal film as the laser absorber, few research reports related to the welding interface morphology and the causes have been published. In this study, carbon black coated copper film was selected as the laser absorber for polycarbonate (PC) laser transmission welding. Three typical fracture forms were analyzed and the relevant welding strength and width were also listed. In order to research the welding interface morphology and chemical bond distribution, the morphology of welding interface on the longitudinal section was observed by optical microscope and the tests of scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) on the cross section were performed. Dispersive bubbles and undulated copper film were found around the welding interface. To prove the causes of multiple undulating features, a thermal expansion test and thermal stress simulation analysis were done. The results indicated the expansion of PC has a more significant impact on the form of thermal stresses and the thermal stresses around the laser spot lead to the formation of multiple undulations at the weld.