Difference In Thermal Expansion Coefficients Research Articles

Employment of 3D-Printed Bilayer Structures with Embedded Continuous Fibers for Thermal Management Applications: An Axial Cooling 4D-Printed Fan Application Case Study.

Bi-material composite structures with continuous fibers embedded on polymer substrates exhibit self-morphing under thermal stimulus induced by the different coefficients of thermal expansion (CTE) between the two constituent materials. In this study, a series of such structures are investigated in terms of fiber patterns and materials to achieve programmable and reversible transformations that can be exploited for thermal management applications. Stemming from this investigation’s results, an axial cooling fan prototype is designed and fabricated with composite blades that passively alter their shape, specifically their curvature and twist angle, under different operating temperatures. A series of computational fluid dynamics (CFD) simulations are performed, subjecting the fan’s geometry to different flow temperatures to measure differences in airflow deriving from the induced shape transformations. Corresponding experimental trials are additionally performed, aiming to validate the simulation results. The results indicate the potential of utilizing bilayer self-morphing configurations for the fabrication of smart components for cooling purposes.

Non-thermal and thermal effects on mechanical strain in substrate-transferred wafer-scale hBN films

Wafer-scale thin films of hexagonal boron nitride have exceptional thermal and mechanical properties, which harness the potential use of these materials in two-dimensional electronic, device applications. Along with unavoidable defects, grains, and wrinkles, which develop during the growth process, underlying substrates influence the physical and mechanical properties of these films. Understanding the interactions of these large-scale films with different substrates is, thus, important for the implementation of this 2D system in device fabrication. MOVPE-grown 2 and 30 nm hBN/sapphire films of size 2 in. diameter are delaminated chemically and transferred on quartz, SiO2/Si, and sapphire substrates. The structural characteristics of these films are investigated by employing Raman spectroscopy. Our results suggest that not only the roughness but also the height modulation at the surface of the substrates play a pivotal role in determining substrate-mediated mechanical strain inhomogeneity in these films. The statistical analysis of the spectral parameters provides us with the overall characteristics of the films. Furthermore, a Stark difference in the thermal evolution of strain in these films depending on substrate materials is observed. It has been demonstrated that not only the differential thermal expansion coefficient of the substrates and the films, but also slippage of the latter during the thermal treatment determines the net strain in the films. The role of the slippage is significantly higher in 2 nm films than in 30 nm films. We believe that the observations provide crucial information on the structural characteristics of the substrate-coupled wafer-scale hBN films for their future use in technology.

Discussion on the Causes of Cracking and Failure of Anticorrosion Layer of a Pipeline

The cause of a rare cracking failure accident of the polyethylene (PE) anti-corrosion layers of a pipeline is analyzed and determined. The properties of the PE raw materials and the anti-corrosion layers were detected and analyzed according to the standard, and the micro-morphology of the anti-corrosion layers was characterized by the scanning electron microscope (SEM). The storage modulus and loss of the anti-corrosion layers at the range of -100~40 °C were tested by the dynamic mechanical analysis (DMA), and the stress of the anti-corrosion layers at low temperature (-40 °C) was calculated. The average thermal expansion coefficient of the anti-corrosion layers in the range of -40~60 °C was tested by the thermomechanical analysis (TMA), and the value at room temperature was obtained, which was compared with the value of the steel materials. The failure accidents caused by raw materials and anti-corrosion layers due to the quality problems, as well as aging and damage of anti-corrosion layers are excluded. The SEM results confirmed that the anti-corrosion layers with no obvious large-scale defects, there were microscopic defects less than 1 μm. At the low temperature (-40 °C), the storage modulus of the anti-corrosion layers is 2.58 GPa, and the corresponding stress is 23.99 MPa, which is higher than the tensile strength test value (22.21 MPa). The average thermal expansion coefficient of the anti-corrosion layers is 14.3×10-5/°C, which is higher than that of the steel material (1.2×10-5/°C). The high stress at low temperature (-40 °C) is one of the reasons for induced defects to cause cracks, and the huge difference in thermal expansion coefficient between the anti-corrosion layers and the steel material is another reason for that.

Biaxial stress in La2Ce2O7/YSZ thermal barrier coatings for oxidation evolution

High temperature oxidation could cause the spalling and failure of thermal barrier coatings (TBCs). La2Ce2O7(LCO)/YSZ double-layer TBCs were investigated with high temperature oxidation at 1100 °C, 1150 °C and 1200 °C, respectively. Interfacial crack propagation and TGO growth behavior were comparatively investigated, and the failure of double-layer TBCs is the result of the joint action of interface transverse crack propagation and TGO growth. Due to the difference in thermal expansion coefficients, the YSZ layer is subjected to biaxial stress, which contains the TGO growth stress and the thermal mismatch stress during the oxidation process. The transverse crack propagation was developed at the LCO/YSZ interface and the YSZ/BC interface, eventually. The thermal barrier coatings TGO thickened abnormally at 1000 °C and 1150 °C, while delamination at the LCO/YSZ interface resulted in coating failure at 1200°C. The thermal mismatch stress at the LCO/YSZ interface increased mainly due to the thermal expansion coefficient between LCO and YSZ. Transverse microcracks at the LCO/YSZ interface gradually propagated, resulting in delamination failure to LCO/YSZ. Therefore, the failure mechanism of biaxial internal stress has important guiding significance for the application of double-layer TBCs.

Corrosion Behavior of Spherical Chromium Carbide Reinforced NiCrBSi Hardmetal Coatings in Sulphuric Acid Solution

In the present work, four groups of spherical chromium carbide reinforced NiCrBSi hardmetal coatings were prepared on AISI 4145 steel by plasma transferred arc (PTA) technique. The corrosion behavior of the four as-received hardmetal coatings in 0.5 mol/L H2SO4 solution was investigated by polarization curve and electrochemical impedance spectroscopy (EIS). The results revealed that more Cr-rich carbides (Cr3C2, Cr7C3 and M23(C, B)6) are formed in the chromium carbide reinforced coatings, while for the NiCrBSi hardmetal coating only Cr7C3 carbide was detected by XRD. The polarization results show that the chromium carbide reinforced NiCrBSi hardmetal coatings have positive corrosion potential and lower corrosion current, providing a better protective effect to the substrate metal. The combined effects of Cr-rich carbide ceramic phases and a more stable passive film of Cr2O3 greatly improved the corrosion resistances of the chromium carbide reinforced NiCrBSi hardmetal coatings. The coating with the highest spherical chromium carbide addition has more pores because of the thermal stress due to the difference of thermal expansion coefficient between the NiCrBSi bonding phase and chromium carbide reinforced phase. The negative effects of the pores weaken the corrosion resistance, and the coating with the 30% chromium carbide content shows the best corrosion resistance. For NiCrBSi hardmetal coatings with higher reinforced chromium carbide content, the repeatability of the corrosion current obtained by polarization fitting is not as good as that of coatings with lower chromium carbide content. The repeatability of polarization results becomes worse when the specimens keep in a more stable passive state.

Electro-thermally driven biaxial bending artificial muscle based on oriented graphite nanoplate nanocomposite/polyimide complex structure

In recent years, artificial muscle is of great research interest due to its promising application. However, low deformation, complicated fabrication process, and high cost hinder their development. Herein, electro-thermally driven biaxial bending artificial muscle based on oriented graphite nanoplate nanocomposite (GN)/polyimide (PI) complex structure is successfully fabricated by cost-effective process utilizing coefficient of thermal expansion difference between them. GN/PI bi-layer films were further assembled and packaged into multi-unit biaxial bending actuator, which could extend and contract like artificial muscle. The unique characteristics of large deformation, easy control, low cost and simple fabrication process distinguish the GN/PI bi-layer based artificial muscle from others. Driven by the voltage of 10 V, the artificial muscle could reversibly reach a shrinkage rate of 11% and a maximum lifting height of 2.5 cm with the object weight of 5.0 g. Moreover, a walking robot has also been designed to achieve a large displacement.

Characterization of residual stresses in fiber metal laminate interfaces – A combined approach applying hole-drilling method and energy-dispersive X-ray diffraction

Fiber metal laminates (FMLs) can be manufactured by direct bonding of fiber reinforced plastics (FRP) and metals using advanced manufacturing approaches, e.g., the prepreg-press-technology. Such materials gain high interest in lightweight applications as they benefit from the superior characteristics of both materials. However, residual stresses are induced in the manufacturing process mainly due to the difference in thermal expansion coefficients between FRP and metal. These residual stresses can lead to the delamination at the transition zone/ interface between FRP and metal and, thus, detrimentally affect the structural integrity and the durability of the FML structure.The objective of the present work is to introduce reliable experimental approaches to accurately measure the distribution of residual stresses across the thickness of the FML, with a special focus on the interface between metal and FRP. Symmetric FMLs with a specific stacking sequence of FRP/steel/FRP are designed and fabricated for residual stress analysis using different approaches, i.e., relaxation and diffraction methods, as well as for results comparison and validation purposes. The incremental hole drilling method (IHD) is used to determine the residual stresses across the thickness of the FMLs. By choosing FRPs with a relatively small thickness, a reliable measurement using IHD can even be achieved across the transition zone between FRP and metal. The energy-dispersive X-ray diffraction method (ED-XRD), as an advanced non-destructive approach, is employed for in-depth residual stress measurement in the metallic part of the FMLs. Each measurement method is characterized by its own advantages, intrinsic limitations as well as uncertainty sources. The obtained results give confidence that both methods are able to assess the qualitative distribution as well as the absolute magnitudes of residual stresses in the FMLs. Based on the approach detailed the reliability of the two measurement methods is cross-validated.

Dependence of surface residual stress on the coefficient of thermal expansion for materials subjected to laser peening without coating

We applied single laser pulse irradiation and laser peening without coating (LPwC) to materials that had different coefficients of thermal expansion (CTEs) to confirm the thermal effects on the surface residual stress (SRS) of the materials. First, 1000 MPa-grade high-strength steel (HT1000) and silicon nitride ceramics (Si3N4) were irradiated underwater with one pulse of a frequency-doubled Q-switched Nd:YAG laser. Si3N4 was also subjected to multiple-pulse laser irradiation of 2, 4, and 10 pulses on the same spot. The SRS within the laser-irradiated spots was measured by X-ray diffraction (XRD); the results showed that the SRS on HT1000 ranged from 600 to 700 MPa in tension, whereas the SRS on Si3N4 with a lower CTE was approximately 300 MPa in compression. Next, Fe-Ni low-expansion alloys with different CTEs were fabricated and subjected to LPwC followed by XRD; their characteristics were compared with SUS304, Alloy600, and Si3N4. The results showed that the SRS was closely correlated with the CTE of the materials. The SRS of Fe-Ni low-expansion alloys tended to be compressive, even under LPwC conditions where the SRS would not be sufficiently compressive for materials that had a high CTE, such as SUS304 and Alloy600, suggesting that CTE is an important index that is closely related to SRS status after LPwC. The SRS of Si3N4 with a low CTE was always approximately 300 MPa in compression, regardless of the pulse density, including single- and multiple-pulse laser irradiation. These results indicated that the SRS of Si3N4 became saturated in a compressive state after single pulse irradiation.

Control of multi-scale cracking for improvement of the reliability of carbon/carbon composites via design of interlaminar stress

Controlled cracking at micro/mesoscale is crucial for decreasing the strength scatter and improving the reliability of carbon/carbon composites (C/Cs). In this work, the controlled cracking is realized by a designed interlaminar residual thermal stress (RTS), which is introduced inside the C/Cs by the alternate stacking of two types of C/C plies with different coefficients of thermal expansion. Firstly, multiscale finite element (FE) modeling is performed to capture the interlaminar RTS induced by the alternate stacking and evaluate the risk of delamination due to the free edge effect. Secondly, mechanisms responsible for the controlled cracking are elaborated with the aid of the FE modeling and experimental characterizations, and the controlled deflections and bifurcations of the crack strongly shield the influence of multiscale flaws. Finally, by adopting this strategy, the flexural strength of the C/Cs increases by 66% while the statistical Weibull modulus also increases from 4.9 to 8.3, verifying the simultaneously improved strength and reliability of the C/Cs.

Microstructures and mechanical properties of YG18 cemented carbide/40Cr steel joints vacuum brazed using Ag–Cu–Ti filler metal

YG18 cemented carbide and 40Cr steel were brazed using Ag–Cu–Ti filler metal under vacuum, and the microstructural evolution of the YG18/Ag–Cu–Ti filler metal/40Cr steel brazed-joint interface was investigated to determine how brazing temperature affected the brazed-joint microstructure, bonding strength, and fracture behavior. At the YG18 cemented carbide/filler metal interface, Ti atoms in the filler metal and C atoms in the YG18 cemented carbide formed a continuous TiC layer, reducing the difference in thermal expansion coefficients between the YG18 cemented carbide and filler metal. At the 40Cr steel/filler metal interface, Ti atoms in the filler metal and C atoms in the 40Cr steel formed a continuous TiC layer, preventing the diffusion of Fe atoms to the cemented carbide side and formation of a hard, brittle phase. YG18 cemented carbide/TiC/Cu2Ti/Ag–Cu eutectic + TiCu granules/TiC/40Cr steel-brazed joints were obtained. With increasing brazing temperature from 860 to 920 °C, the bonding strength of the YG18 cemented carbide/40Cr steel joint initially increased and then decreased. The joint brazed at 900 °C for 10 min failed in the middle of the brazing seam, and its average bonding strength was 235 MPa.

Development of Reversible Ni-Fe Metal Supported Solid Oxide Cells

Reversible Solid Oxide Cells (RSOCs) are bi-functional energy conversion devices for generating electricity and producing fuels (H2 and CO) with high efficiency and fuel flexibility. Conventional ceramic supported RSOCs have limitations in commercialization due to mechanical issue, so a metal support with thermomechanical stability has been proposed. Thermal expansion coefficient (TEC), conductivity and diffusion behavior of metal support can be simply adjusted by composition control. Herein, we maximized the electrical, chemical and contact properties of the Ni-Fe metal support by controlling the Fe2O3 contents to 10-90 wt% (10 NiFe, 50 NiFe, and 90 NiFe). 50NiFe showed high electrical conductivity and low Fe diffusion into the functional layer based on high alloy content. In addition, good contact was obtained without structural defects due to the appropriate TEC difference with the other components. 50 NiFe | Ni-YSZ | ScSZ | LSM-ScSZ single cell showed excellent performance with maximum power density of 2.4 W cm-2 in 3%H2O/H2 in fuel cell mode and a current density of 2 A cm-2 at 1.4 V in 50%H2O/H2 in electrolysis cell mode at 800oC. The electrochemical performance of the cell shows stable operation during 30 cycles electrolysis cell/fuel cell for 5 hours. The results demonstrate the potential for commercialization of long-lasting high performance and cost-efficient RSOCs in a broad range of fields.

A high-temperature adhesive for stainless steel 304: Effect of Cr growth at the interface of alkali silicate adhesive

With the recent advancements in the aerospace industry, the demand for adhesive materials with resistance to high temperatures has increased. Although the existing organic adhesive materials have a high adhesion strength, their heat resistance and pyrolysis temperature are low, thus limiting their application under high-temperature conditions. Therefore, we attempted to bond stainless steel 304 using an alkali silicate, an inorganic material-based adhesive with high heat resistance but low adhesive strength and analyzed the effects of surface oxidation of stainless steel 304 on its adhesion strength. The surface treatment of SUS304 was performed using mechanical polishing (MP) and electropolishing (EP). A Cr 2 O 3 dominant layer (CODL) and a Fe 2 O 3 dominant layer (FODL) were formed by heat treatment. The adhesion failed in MP, EP, and CODL specimens, when bonding was performed using mixed silicate (MS) because of the differences in thermal expansion coefficients between the metal and glass. FODL and CODL + FODL specimens displayed MS and adhesion strengths of 8.45 MPa and 11.36 MPa, respectively. Each surface and adhesion interface was analyzed through X-ray diffraction (XRD), cross-section scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS), before and after adhesion. When CODL and FODL specimens were placed on both sides to bond with the MS, a needle-like Cr structure appeared on the MS layer from the Cr 2 O 3 layer that enhanced the mechanical adhesion with the MS and the overall adhesive strength. Based on these findings, we conclude that the adhesion strength can be improved by combining a CODL specimen and a FODL specimen and bonding with glass.

Theoretical Study on the Structural, Elastic, Electronic and Thermodynamic Properties of Long-Period Superstructures h- and r-Al2Ti under High Pressure.

The formations of long-period superstructures strongly influence the properties of Al-rich L1-TiAl intermetallic alloys. To soundly understand the role of the superstructures in the alloys, fundamentals about them have to be known. In the present work, the structural, elastic, electronic and thermodynamic properties of h- and r-AlTi long-period superstructures under pressure up to 30 GPa were systematically investigated using first-principles calculations based on density functional theory. The pressure dependence of structural parameters, single-crystal elastic constants, polycrystalline elastic modulus, Cauchy pressures and elastic anisotropy were successfully calculated and discussed. The total and partial densities of states at different pressures were also successfully calculated and discussed. Furthermore, combining with quasi-harmonic approximation, the effects of the pressure on the temperature dependent volume, isothermal bulk modulus, thermal expansion coefficient, heat capacity and Gibbs free energy difference were successfully obtained and discussed. Our results were consistent with the available experimental and theoretical values.

Fabrication of Cu-adhered silicon carbide particles and its effect on properties of Fe-based matrix composites

In present study, copper powders (Cu) and silicon carbide (SiC) particles were used to produce Cu-adhered SiC particles (Cu/SiC), which were used to reinforce Fe-based matrix materials to modify properties. The orthogonal experimental design was used to investigate the relationship between ball mill parameters and particle size. Next, the mixed powders were pressed at 500 MPa using a hydraulic press. Then, the green compacts were wrapped in graphite powders, and sintered using a resistance furnace. Metallurgical microscopy, scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDS) and x-ray diffraction were employed to investigate the microstructures, element distribution, and phase of SiC-reinforced Fe-based matrix composites. The properties of the SiC-reinforced metal matrix composites were determined using the Microhardness test and Charpy pendulum impact test. The orthogonal experimental results indicated that the influence degree of milling parameters on particle size was the powder to ball ratio>milling time>milling speed. The milling parameters to obtain the smallest Cu/SiC particle were powder to ball ratio of 20:1, milling time of 15 h, and milling speed of 300 r min−1. However, the adhesive effect was bad. The properties test results indicated that Cu/SiC particles reinforced with Fe matrix composites had better properties. Furthermore, the hardness and impact toughness improved up to 239.97 HV0.5 and 12.1 KJ·m−2, respectively. Moreover, compared to raw SiC particles, the hardness and impact toughness increased by 12% and 15%, respectively. The improvement in properties was attributed to the Cu adhesion to the SiC surface, which effectively alleviated the difference in thermal expansion coefficient between SiC and Fe, and formed a chemical bond at the interface to improve the interfacial binding

Dual-mode biomimetic soft actuator with electrothermal and magneto-responsive performance

Soft actuators with large deformation and high stability in response to multi-stimuli are highly demanded in biomimetic applications. However, most of the present actuators driven by a single stimulus often exhibit low performance and high energy consumption. In this work, a sandwich structural soft actuator (MPDMS/MXene/PTFE) which possesses electrothermal/magnetic coupling actuation is fabricated by combining magnetic NdFeB/Polydimethylsiloxane (MPDMS) composite layer, MXene film, and PTFE tape together. Due to the large difference of thermal expansion coefficient between MPDMS film and PTFE tape, the soft actuator shows a wonderful electrothermal actuation and the bending deformation can reach to as high as 353° under a 3 V power supply. The excellent electrical conductivity of MXene component endows the sandwich film with good thermal management performance, thus the soft MPDMS/MXene/PTFE sandwich films can be applied in the thermal treatment of body and thermal imaging. Most importantly, the soft actuator also exhibits a typical magnetic biomimetic actuation and the programmable actuation performance of the dragonfly actuator can be demonstrated by both experiments and finite element simulations. Eventually, the electrothermal/magnetic coupling actuation is successfully applied in an intelligent crawling robot to overcome the traditional inchworm movement simulation.

Effect of temperature variation on the plate-end debonding of FRP-strengthened steel beams: Coupled mixed-mode cohesive zone modeling

Fiber-reinforced polymer (FRP) strengthened steel beams may experience significant temperature variation during their service life. Because of the different coefficients of thermal expansion (CTEs) of FRP and steel materials, thermal stresses can be generated by temperature variation at the FRP-to-steel interface and consequently influence the plate-end debonding mechanism. Therefore, an accurate prediction of the debonding failure of FRP-strengthened steel beams under combined mechanical and thermal loading is of great importance for the strengthening design. This paper proposes a closed-form analytical solution based on a coupled mixed-mode cohesive zone model (CZM) (i.e., with the consideration of Mode-I and Mode-II mixity), to analyze the effect of thermal stress on the debonding failure of FRP-strengthened steel beams. An excellent agreement has been achieved between the analytical solution and the finite element (FE) modeling in terms of interfacial full-range debonding behavior. Further parametric studies were conducted and indicated that the thermal stresses induced by elevated temperatures tend to reduce the plate-end debonding load and such effect becomes more significant when a thicker FRP plate is adopted.

ZnO Piezoelectric Films for Acoustoelectronic and Microenergetic Applications

Zinc oxide is one of the most popular materials for acoustoelectronic sensors and vibro-piezo-transducers used in nano-piezo-generators. In the present paper, thick piezoelectric ZnO films are fabricated on both sides of various substrates using magnetron sputtering technique. It is shown that the main problem for double film deposition is the difference in thermal expansion coefficients of the ZnO films and the substrate materials. The problem is solved by decreasing the plate temperature up to 140 °C, reducing the growing rate up to 0.8 ± 0.05 μm/h, and diminishing the oxygen content in Ar mixture up to 40%. Using the modified sputtering conditions, the ZnO films with thickness up to 15 μm, grain size 0.3 μm, and piezoelectric module as large as 7.5 × 10−12 C/N are fabricated on both faces of quartz and lithium niobate plates as well as on flexible polyimide flexible film known as Kapton. The films are characterized by chemical composition, crystallographic orientation, piezoelectric effect, and acoustic wave generation. They are applied for vibro-piezo-transducer based on flexible ZnO/Kapton/Al/ZnO/Al structure. When the structure is mechanical excited, the variable electric voltage of about 35 mV is generated. The value of the voltage is sufficient for an unstable energy source used in autonomic micro-energetic energy-store systems.

Simultaneous transverse loading and axial strain for REBCO cable tests in the SULTAN facility

We present the design and first results of an assembly that enables rare earth barium copper oxide (REBCO) superconducting cables—the VIPER cable in this work—to be tested in the SULTAN facility under the simultaneous application of transverse electromechanical loading and axial mechanical strain. The objective is to emulate the loads that a REBCO cable would experience in a three-dimensional coil but in shorter and simpler straight cables, reducing the cost, schedule, and complexity of high-fidelity conductor qualification. The assembly uses two methods for inducing axial strain in the cables. First, hydraulic jacks stretch the assembly and inserted Invar shims lock in up to ∼0.3% axial cable strain on the benchtop at room temperature. Second, the different coefficients of thermal expansion between Invar clamps and the copper cable are exploited to induce an additional ∼0.3% axial strain on the cable when the sample is cooled in the SULTAN test well from room temperature to below 50 K. Finite element analysis modeling shows that the soldered matrix of the VIPER cable transfers approximately 50%–60% of the external cable strain into the REBCO stack. The assembly was successfully employed at SULTAN, enabling two VIPER cables to be cycled 500 times at 382 kN m−1 transverse electromechanical loads with ∼0.5% mechanical strain on the cable (corresponding to ∼0.3% mechanical strain in the REBCO stacks) demonstrating critical current degradation stabilizing after 30 cycles at less than 5% and providing confidence in VIPER cables under realistic high-field magnet conditions.

Bio-inspired soft actuator with contact feedback based on photothermal effect and triboelectric nanogenerator

The development of film soft actuators with contact feedback and outstanding environmental robustness is desirable. In this work, a film-based soft actuator laminated by polyethylene glycol terephthalate (PET), carbon black ink, and polydimethylsiloxane (PDMS) is proposed. Due to the enormous difference in thermal expansion coefficients between these materials, the actuator achieves a large bending deformation angle and a high response speed. Without the shape-memory materials, the actuator can return to its original shape under light-induced after being subjected to mechanical stress. Meanwhile, the actuator maintains its shape after being exposed to extreme temperatures of up to 200 °C and immersion in a variety of solvents. Furthermore, based on the triboelectric effect, the actuator can generate remarkable real-time electrical signals when it mimics the tongue of frogs, bends deformation, and simulates mechanical grippers. This work demonstrates a simple method for building various intelligent and flexible electronic devices and provides promising applications for soft robots.

Evolution Behaviors and Reduction Mechanism of Curing Residual Stresses in GLARE Laminates under a Hot-Pressing Condition.

Nowadays, variable preparation, forming and processing methods of fiber metal laminates are constantly developing to meet the requirements of different application fields, hence the characteristics and evolution of residual stresses under different manufacturing conditions deserve more attention. In this work, the evolution behaviors of curing residual stresses in GLARE under a hot-pressing condition were studied, and the residual stress reduction mechanism was also explained. Results suggested the FE prediction models of the entire cure process, verified by the fiber Bragg grating (FBG) sensors, were more precise than the traditional elastic model. Moreover, the stress evolution during the cure process mainly occurred in the cooling stage, in which the different coefficient of thermal expansion (CTE) of aluminum and GFRP played a major role. Meanwhile, curing shrinkage stress in the GFRP layer during the holding stage at curing temperature obviously influenced the final stress level. The residual stresses in GFRP layers differed by 9.6 MPa under a hot-pressing and autoclave condition, in which the convection heat transfer condition played a major role as it caused lower thermal stress in the holding stage and a smaller temperature gradient in the cooling stage. Considering this, a lower cooling rate could be a feasible way to obtain GLARE with lower residual stress under a hot-pressing condition.