Thermal Cycling Environments Research Articles

Low-velocity impact behaviors of TFMLs in hydrothermal and thermal-cycling environments

Thermoplastic fiber metal laminates (TFMLs) have garnered significant attention due to their excellent impact resistance. However, the influence of practical environmental factors on the impact resistance of TFMLs remains inadequately explored. This study endeavor to investigate the impact behaviors and damage tolerance of TFMLs, employing a novel thermoplastic resin, Elium®188, under two simulated marine environments: a thermal-cycling condition (involving 90 days of exposure to 70℃ for 6 h followed by 18 h at room temperature daily) and a hydrothermal environment (consisting of 90 days of immersion in distilled water at 70℃). The impact response and damage characteristics were analyzed through low-velocity impact (LVI) and compression-after-impact (CAI) tests. The findings indicated that under thermal-cycling, the LVI resistance decreased as a result of resin aging, but the resin hardened during aging led to a 48 % increase in CAI strength over the 90-day period. In the hydrothermal environment, the absorbed energy decreased by 5.6 % and CAI strength decreased by 13.7 % after 90 days, primarily due to resin hydrolysis and erosion of the TFMLs’ internal structure by water molecules. This research offers valuable insights into the impact resistance and damage tolerance of TFMLs, serving as a vital reference for practical applications in marine settings.

On the mechanical behavior of carbon fiber/epoxy laminates exposed in thermal cycling environments

Carbon fiber reinforced polymer (CFRP) composites are commonly used for reflectors of artificial satellites operating in low earth orbit (LEO). The decay of the modulus of the CFRP composite varies under different thermal cycling environments, which can lead to a reduction in the accuracy of the reflector panels, affecting the transmission of signals. This paper investigates the impact of different thermal cycling conditions on the mechanical behavior of carbon fiber/epoxy laminated composites experimentally. Three kinds of thermal cycling conditions involving continuous temperature changes are employed to explore the influence of temperature range on the residual tensile and in-plane shear moduli of the laminates. Test results indicate that the upper temperature limit and the temperature span of the thermal cycling conditions jointly affect the mechanical properties of CFRP composite laminates, but the responses of the residual tensile and in-plane shear moduli are different under the variation of each temperature parameter alone. The residual tensile and in-plane shear moduli of the laminates under thermal cycling decrease with an expansion of the temperature span having the same upper limit. If the temperature span remains constant, an increase in the upper temperature limit leads to an increase in the residual tensile modulus, but a decrease in the residual in-plane shear modulus. The main damages causing the decay of residual tensile and in-plane shear moduli of unidirectional laminates were investigated by scanning electron microscopy (SEM) technology. Observations of the microscopic fracture of the material show that the post-curing reaction factor predominantly influences the residual tensile modulus of unidirectional laminates, while the fiber/matrix interface damage factor dominates the residual in-plane shear modulus of the unidirectional laminates. Furthermore, an increase in the fiber tensile modulus decreases both residual tensile and residual in-plane shear moduli. Notably, the residual in-plane shear modulus exhibits greater sensitivity to thermal cycling compared to the residual tensile modulus. The findings reported in this paper would provide valuable insights and guidance for the design and application of carbon fiber/epoxy composites subjected to thermal cycling conditions.

Characterization on fatigue behavior and damage mechanism of C/BMI composites experienced thermal cycling

The multi-directional laminate CCF800H/AC631 bismaleimide composite material was exposed for a long time under the thermal-cycling environment (−60°C ∼+180°C), and the mass loss rate, FTIR spectra, DMA, tensile strength were tested. The fatigue stress level was determined according to the tensile strength and the fatigue performance of the before and after the thermal-cycling environment was tested. Macroscopic visual inspection and ultrasonic C-scan were used to characterize and analyze the fatigue damage of composite materials. The results show that with the increase in the number of thermal cycles, the mass loss of the composite material started with increased rapidly and then basically flat. The C/BMI composites underwent obvious thermal oxygen aging. After thermal-cycling, it would lead to changes in dynamic mechanical properties by a certain degree of post-curing, physical aging, and local interface debonding in composite materials. With the thermal cycles increased the composite material tensile strength first increased slightly and then decreased rapidly. After 300 thermal cycles, the composite materials occurred slightly damaged, and the fatigue life was apparently reduced compared with the original state. The fatigue failure modes of composite materials are mainly fiber fracture and multi-directional laminate delamination. At high stress levels, the stiffness of the specimen after thermal-cycling are lower decrease compared with original specimens, more stress levels would lead to more II stage rate of stiffness decline, and stiffness degradation curve and hysteretic energy recovery curve had enough effect to characterize damage effect of material environment induced by thermal-cycling environment factors.

The Effect of Thermal Cycling on the Tensile and Shear Behaviors of the Carbon Nanotube-Reinforced Epoxy

The aim of this research is to study the tensile and shear properties and mechanical behavior of carbon nanotube- (CNT-) reinforced epoxy after the resulting composites have been exposed to different thermal cycling environments. Single-walled carbon nanotubes (SWCNTs) are cylindrical molecules that consist of rolled-up sheet of single-layer carbon atoms (graphene) with a diameter of less than 1 nanometer (nm). Thermal cycling environments can exist in many conditions, such as in-earth orbit for satellites which rotate around the earth and pass through the sun illumination and earth’s shadow, and for airplanes which fly in different altitudes with different temperatures. Carbon nanotube-reinforced epoxy is one of the nanocomposite materials which have been broadly used in many applications such as aerospace, automotive, electronics, and other industries. The goal of this study is to fabricate this nanocomposite with different multiwall and single-wall CNT concentrations and expose it to different thermal cycle numbers and determine the changes in tensile and shear properties and failure characteristics. For this purpose, tension and short-beam tests have been used in this research. The addition of multiwall CNT produces better mechanical properties compared to the use of SWCNT reinforcement. However, unreinforced epoxy showed the highest mechanical properties.

Operation Performance Test of Aerospace Mechanical Pumps and Verification of Their Environmental Adaptation

In this paper, one aerospace centrifugal pump with flowrates of 1~2g/s was developed which was applicable to the mechanically pumed two phase loop (MPTL) system. Moreover, an experimental test platform was built to test and verify the performances of pump. Besides, the environmental adaptation tests of the designed pump were verified. Results show that: 1) the flow rate and lift of the pump at the rated working point are 2.043g/s and 0.0517MPa, while the input power is only 9.92W. These can meet requirements of the design indexes. 2) The input power is only 4.71W under the two-phase operation state and this pump can transfer the heat of 240W, and the pump shows a very high energy efficiency ratio (EER). 3) The lift of designed pump is constant at specified rotation speed and it can assure the temperature stability of MPTL system. 4) This pump can meet the requirements of services in vibration, vacuum and thermal cycling environments.

Effect of different thermal change tests of micro tensile strength behavior bio-composite materials; In vitro study

Background: The thermal changes in environments that composite materials are exposed to has a great effect on fatigue and wear behavior. Aim: Micro-cracks and interfacial deformations occur in the composite material structure because of heating and cooling environments occurring on material surfaces. Considering the environment to which bio-composite materials used in the human body are exposed, it is inevitable that they are exposed to a thermal change cycle environment. Material and Method: In this study, the mechanical behaviors of Silorane, X-Trafil and Valux-Plus bio-composite materials were examined after being exposed to thermal cycles in an artificial mouth environment in the temperature range of minimum 5 °C and maximum 65 °C. Micro-tensile strengths of bio-composite materials after thermal cycle test procedures were determined using a universal micro tensile tester device. In addition, microstructural analyzes of bio-composite materials were evaluated using scanning electron microscopy (SEM). Results: Within the scope of the data obtained as a result of this study, it was concluded that the thermal changes in environments significantly affects the micro-shrinkage behavior of bio-composite materials. Conclusion: The behavior of the matrix structure of the composite material significantly affected the formation of micro cracks.

Degradation prediction of encapsulant-glass adhesion in the photovoltaic module under outdoor and accelerated exposures

Maintaining good encapsulant-glass adhesion is important to ensure the long-term durability of photovoltaic (PV) modules. An exposure dose based model was used in this study to predict the temporal and spatial degradation of encapsulant-glass adhesion inside the PV module under hygrothermal exposure. The exposure dose is a single parameter that combines the exposure temperature, humidity and time using an exponential relation that is governed by a degradation activation energy. Peel tests were used to measure degradation in ethylene–vinyl acetate (EVA)-glass adhesion in PV module laminates that are aged under various constant temperature and humidity environments. An optimization technique applied to fit an exponential relation between the degraded adhesion strength and exposure dose gave the degradation activation energy as 59.4 kJ/mol.The model was used to study EVA-glass adhesion degradation for glass-glass and glass-backsheet based PV modules exposed to 5 year outdoor (Delhi, India), damp heat, humidity freeze and thermal cycling environments. The spatial and temporal distribution of relative humidity at the EVA-glass interface inside the PV module was predicted considering Fickian diffusion in the backsheet and EVA. The predicted humidity is used to estimate the exposure dose, which is further used to predict adhesion degradation. The highest degradation in all exposures occurs at the edge for the glass-glass module, whereas near the gap between cells for the glass-backsheet module. The integrity of the interface near the exposed boundary can be assessed by the damp heat exposure, but the integrity away from the boundary cannot be assessed by the accelerated exposures.

Review on adaptive control of laser-directed energy deposition

Laser directed energy deposition (LDED) is one of the most important parts of metal additive manufacturing, which can provide fast building speed, allows for large building volumes, and is suitable for part repair. LDED can manufacture components layer by layer through processes of rapid heating, melting, solidification, and cooling with the laser beam as a heat source. However, deposition quality and repeatability of components produced by LDED are poor because of the complex thermal cycle and processing environment, hindering the spread of this technique. Adaptive control technology (ACT) is consistently considered an effective and potential way to solve the problem. Many studies have focused on LDED and established the relations of process parameters, process signatures, and product qualities, which promote the rapid development of ACT, with the development of monitoring devices and data processing technology. We review and discuss the problems existing in the ACT of LDED.

A Method of HCN Gas Spectrum Denoising and Baseline Removal Used for FBG Interrogation

Hydrogen cyanide (HCN) gas based fiber Bragg grating (FBG) interrogation is a promising approach in thermal cycling environment. However, the HCN spectrum suffers from strong noise and baseline wander induced by the interrogation system, which limits the measurement stability and reliability. In this paper, we propose an integrated method for spectral denoising and baseline removal to improve the interrogation performance. The method combines the classical empirical mode decomposition (EMD) with the recently developed convolution window (CW) filtering. After the HCN spectrum is decomposed by EMD, the noise and baseline components are extracted from the intrinsic mode functions via a “multiband” filtering approach. Verification experiments are performed using HCN gas cells with different absorption spectra. The results show that the proposed method is able to remove both noise and baseline with minimum signal distortion. Compared with other methods, the optimal interrogation stability with 25 Torr HCN gas cell is improved from ±1.43 pm to ±0.87 pm. For the 100 Torr HCN gas cell, the optimal interrogation stability is improved from ±1.75 pm to ±0.99 pm. In addition, the proposed method also improves the reliability of the interrogation system in the case of large light attenuation.

Effect of Thermal Cycling on Operational Characteristics and Lifetime Prediction of Space Pulse Tube Refrigerator

This paper presents the operation status and results of ground thermal cycling test of pulse tube refrigerators (PTRs) for space application. Firstly, a thermal cycling degradation model was proposed by considering two physical mechanisms: contamination and fatigue damage. Then, a thermal cycling test scheme of two types of PTRs was designed and performed to demonstrate their long lifetime and high thermal stability. Two type A PTRs with cooling capacity of 1W@60 K and two type B PTRs with cooling capacity of 5W@80 K were continuously operated for about two years in a simulated vacuum thermal cycling environment. Effects of heat rejection temperature variation on thermal stability and dynamic performance of the PTRs were investigated. Furthermore, the thermal cycling degradation model was validated with the actual thermal cycling test data. Finally, the predicted pseudo-failure lifetime was acquired via experimental data and degradation model. Moreover, the estimated reliability of PTRs was obtained through using the Weibull distribution. The proposed thermal cycling test scheme and innovative lifetime prediction and reliability estimation method provide a quick and accurate approach for the cooler manufacturer to assess the lifetime and reliability of the space PTRs.

Study of low earth orbit ultraviolet radiation and vacuum thermal cycling environment effects on epoxy-based shape memory polymer

Shape memory polymers have been studied as the matrix of lightweight self-deployable space structures for decades. The epoxy-based shape memory polymer, which is a potential material for aerospace application, has been tested about their resistance abilities to the ultraviolet radiation and vacuum thermal cycling by using ground-based simulation facilities. The wavelength of ultraviolet radiation is 250–400 nm with not less than five times the solar constant, and the irradiation times are 80, 160, and 240 h, respectively. The vacuum level, temperature range, and cycling times of vacuum thermal cycling are 10−5 Pa; −100°C to +100°C; and 0 cycle and 15, 30, and 45 cycles, respectively. The shape memory polymer specimens are compared for mass loss ratio, chemical compositions, surface morphology, and mechanical properties before and after the ultraviolet radiation and thermal cycling. The experimental results indicate that the glass transition temperature (Tg), mass loss ratio, modulus, and yield and break strength increase after experiencing 240h ultraviolet radiation or 45 thermal cycles, which shows great potential of epoxy-based shape memory polymer in aerospace structures and device applications.

Large angle flexure pivot development for future science payloads for space applications

An innovative design of a Large Angle Flexure Pivot (LAFP) is described. It combines the advantages of flexure mechanisms while surpassing one of their few flaws, small displacement strokes. The LAFP design exceeds these angular limitations to reach a deflection of 180° (±90°). The centre shifts laterally by less than ±35 μm throughout the full rotation range. The LAFP is meant to be mounted in pairs, coaxially and with the payload between them. The intended application of the LAFP is to angularly guide an optical component in a space environment for future science missions operating in a cryogenic environment. A dedicated performance test bench was developed and manufactured to test the pivot characteristics notably the lateral shift using Eddy current sensors. The test bench incorporates a representative dummy payload for mass and inertia. Extensive FEM analysis has been performed to validate the design at component level and further analysis with the pivots mounted with a representative payload on a test bench for random vibration, shock and thermal cycling environment. The second test bench for the vibration and shock tests has been manufactured incorporating a simplified launch locking device. The performance tests have confirmed a lateral shift of less than ±35 μm over an angular range of ±90°. The pivots have been successfully tested and survived vibration loads for high level sine at 24 g and random vibration at 12 grms in all three directions.

A novel low colored and transparent shape memory copolyimide and its durability in space thermal cycling environments

Recently, shape memory polymers (SMPs) with high optical transmittance have been paid great attentions to endow the flexible optoelectronics with shape memory functions. Herein, a low colored and transparent shape memory copolyimide (SMcoPI) is obtained by suppressing the charge transfer complex interactions. The optical transmittance of the synthesized SMcoPI film could reach at ∼86% at the wavelength of 450 nm, far higher than the nearly zero optical transmittance of yellow and brown Kapton H. The better optical transparency could be attributed to the loose molecular chain arrangements induced by the meta-substituted groups and flexible ether linkages. The glass transition temperature (Tg) range of the synthesized SMcoPI films is from 179 °C to 220 °C, which is higher than that of reported optically transparent SMPs. The effective decomposition temperature at the weight loss of 5 wt% is 517 °C, showing excellent thermal stability. The SMcoPI also demonstrated good shape memory behaviors with high shape recovery ratio (Rr, >96%) and shape fixity ratio (Rf, >97%). In addition, the SMcoPI could maintain high optical transmittance, good thermostability and excellent shape memory behaviors after the ground-stimulated space thermal cycling test for 250 h. The synthesized SMcoPI has application potentials in high temperature areas or optoelectronic devices.

Assessment of the Performance of Sn–3.5Ag/Cu Solder Joint Under Multiple Reflows, Thermal Cycling and Corrosive Environment

The solder joint performance of Sn–3.5Ag/Cu combination was studied under multiple reflows, thermal cycling and exposure to the corrosive environment. Factorial experiment was carried out to assess the effect of individual parameters and the interaction of parameters on the shear strength of the solder joint. The results showed that the combination of thermal cycling and immersion in corrosive media resulted in the maximum decrease in the shear strength followed by the combination of multiple reflows and corrosive media. The shear strength reduced with the increase in immersion duration in corrosion medium. Factorial experiment was analyzed using analyis of variance (ANOVA). The results indicated that the individual parameters had a significant effect, whereas the effect of interaction of these parameters was less significant on the performance of the solder joint. Fracture surface indicated mixed mode of failure and the occurrence of fracture predominantly in the bulk solder.

Self-marked HCN gas based FBG demodulation in thermal cycling process for aerospace environment.

The thermal cycling process experienced by spacecraft during orbital operation would lead to deterioration of the demodulation performance of fiber Bragg grating (FBG). A new demodulation method based on Fabry-Perot (F-P) filter and hydrogen cyanide (HCN) gas is proposed to improve the performance. The method skillfully utilizes the self-marked HCN absorption lines as absolute wavelength references. In the thermal cycling environment whose temperature ranging from 5°Cto 65°C,the fluctuation of demodulation wavelength reduces to ± 2.6 pm, which is improved by 3.1 times compared with traditional method. The proposed method also shows a good robustness in the cases of weak light source intensity and poor signal-to-noise ratio (SNR) of HCN spectrum.

Study on performances of colorless and transparent shape memory polyimide film in space thermal cycling, atomic oxygen and ultraviolet irradiation environments

Shape memory polymers with high glass transition temperature (HSMPs) and HSMP-based deployable structures and devices, which can bear harsh operation conditions for durable applications, have attracted more and more interest in recent years. In this article, colorless and transparent shape memory polyimide (SMCTPI) films were subjected to simulated vacuum thermal cycling, atomic oxygen (AO) and ultraviolet (UV) irradiation environments up to 600 h, 556 h and 600 h for accelerated irradiation. The glass transition temperature (Tg) determined by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) had no obvious changes after being irradiated by varying amounts of thermal cycling, AO and UV irradiation dose. After being irradiated by 50 thermal cycles, 10 × 1021 atoms cm–2 AO irradiation and 3000 ESH UV irradiation, shape recovery behaviors of SMCTPI films also had no obvious damage even if they experienced 30 shape memory cycles, while the surface morphologies and optical properties were seriously destroyed by AO irradiation, as compared with thermal cycling and UV irradiation. The tensile strength could separately maintain 122 MPa, 120 MPa and 70 MPa after 50 thermal cycles, 10 × 1021 atoms cm–2 AO irradiation and 3000 ESH UV irradiation, which shows great potential for use in aerospace structures and devices.

압전 페인트 센서를 활용한 충격 모니터링 활용 방안

Abstract The piezoelectric paint sensor is a paint type sensor comprising of an epoxy and piezoelectric powder, which is the main component of a piezoelectric material. This sensor can be easily attached to any type of structure as compared to other sensors because it is viable to directly apply it on structures, as in the case with a typical paint. In this study, the capability of piezoelectric paint sensor for impact detection was evaluated. In Particular, the applications of the piezoelectric paint sensor for railroad vehicles were considered. There have been various cases reported about the damages caused by flying gravel to the under-cover of the railroad vehicle during operation. In order to prevent this, real-time monitoring of the large under-cover surface of the railroad vehicle is unavoidable. Under the assumption of vehicle application, sensor sensitivities were measured after multiple and prolonged exposure to thermal cycle environment (-20~60℃). Sensitivity evaluation of paint sensor under environmental conditions was conducted in an aluminum specimen. In results, despite the small variations in sensitivity, we could confirm the applicability of this paint sensor for impact detection even after a severe environmental exposure test.

The degradation behavior of UHTCs based coatings coated PIP-C/SiC composites in thermal cycling environment

UHTCs based coatings (ZrB2–SiC coating and ZrC–SiC coating) are prepared on the surface of PIP-C/SiC composites by slurry and CVD method, and the thermal stability is one of the key issues for C/SiC composites. This study aims to study thermal shock behavior of the coated composites. The results show the degradation of flexural strength without obvious variation, and the fracture mode and pull-out mechanism are also changed. The composition of coatings is characterized by XRD, SEM and XPS. The decrease of flexural strength during the tests is due to the debonding of the coating-matrix interfaces. Compared to uncoated C/SiC composites, the UHTCs based coatings are able to improve the mechanical properties of the composites.

The degradation behavior of SiC coated PIP-C/SiC composites in thermal cycling environment

C/SiC composites had been considered as structural material in complex and harsh environments, thermal stability was one of the key issues for C/SiC composites. This study aimed to investigate C/SiC composites in thermal cycling environment. SiC coating on carbon fibers via chemical vapor deposition at time from 0.5 h to 5 h was studied, and then the degradation behavior of coated C/SiC composites had been measured by thermal cycling tests. The results showed that the coating was continuous and uniform, with good surface adhesion. The interface of carbon fibers and SiC coating was partially destroyed during thermal shock tests. The degradation of mechanical properties was closely related to the evolution of the damage in the composites.

A reliability assessment method based on an accelerated testing under thermal cycling environment

This article proposes a reliability assessment method based on an accelerated testing under thermal cycling environment to assess the reliability of an electronic device with multiple failure modes. First, two typical failure modes of the electronic devices in the thermal environment are analyzed. It is concluded that the reliability of a complicated electronic device (with both the two typical failure modes) is difficult to assess through the existing accelerated testing methods. Second, an acceleration model is established by combining the Arrhenius model with the Norris–Landzberg model. The influences of the thermal cycling environment on both the typical failures are taken into account in this model. Third, a thermal cycling test plan is developed, and a new approach is proposed to evaluate the reliability of an electronic device with multiple failure modes. Finally, a numerical example is illustrated to demonstrate the feasibility of proposed method, and the calculation results show the efficiency of the proposed method.