Effects of ageing at 200°C in air for up to 1000h on static mechanical properties and low velocity impact behavior of a carbon fiber (T700) reinforced modified bismaleimide (BMI) composite have been ...investigated. A new C-scan data process method was applied to determine the variation in impact damage model and related failure mechanism due to thermal ageing, and attention was paid mainly to the barely visible impact damage. The transverse tensile strength and interlaminar-shear strength of the composite were found to decrease progressively with increase in ageing time, resulting from degradation of BMI matrix, damage of fiber/matrix interface and formation of microcracks caused by thermal ageing. It was shown that after thermal ageing, the impact damage model of the composite varied from a barely visible impact damage to a visually detectable impact damage as the impact energy reached the range from 20J to 30J. The employed C-scan data process method was proven to be more effective in revealing variation of impact failure mechanisms. It was deduced that the internal delamination dominated the barely visible impact damage model, and fiber breakage became more important in the aged composite as impact energy higher than 20J.
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•A Cf/BMI composite experienced high temperature exposure and remained favorable mechanical performance.•Thermal ageing degraded static mechanical properties by inducing decomposition, interface debonding and microcracks.•A modified C-scan technique was valid in determining efficiency of absorbed energy and impact failure mechanism.•Thermal ageing enhanced critical transition from barely impact damage to visually detectable impact damage.•Barely visible impact damage characteristics and corresponding mechanism of aged composite were revealed.
The effects of vacuum-thermal cycling and hygro-thermal cycling on the fiber/matrix interface characteristics of a carbon fiber reinforced bismaleimide (C/BMI) composite were investigated to assess ...the degradation behavior of the mechanical property of C/BMI composite in low earth orbit (LEO) and atmosphere environment. The feasibility of using one comprehensive accelerated test procedure capable of representing the LEO and atmosphere environmental effects simultaneously for the aerospace plane was explored for the first time. A simplified mathematical approach and the corresponding model was supplied firstly to prove the reliability and effectiveness of the widely-used SEM observation method in the assessment of fiber matrix interface properties. The dominating degradation mechanism of the C/BMI composites caused by vacuum-thermal cycling in LEO environment is the interfacial sliding induced by thermal stress, whereas the thermal oxidation and decomposition of the matrix is the main degradation mechanism after hygro-thermal cycling in atmosphere environment. Candidate composite materials for aerospace plane must be tested in atmosphere and LEO environments separately in the environmental simulation experiments before their application.
The Potassium Titanate-Ti3C2Tx nanocomposite was successfully synthesized by a simple one-step chemical process using Ti3C2Tx and potassium hydroxide at room temperature. Compare to Ti3C2Tx ...nanosheets, the Potassium Titanate-Ti3C2Tx exhibits superior tribological properties.
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A potassium titanate-Ti3C2Tx nanocomposite was synthesized using a facile, low-temperature and environmentally friendly process. The morphology and microstructure of the as-prepared samples were analyzed by means of XRD, SEM, TEM, and XPS. The tribological property of the nanocomposite as additive in base oil was evaluated. The results reveal that the in-situ formed potassium titanate nanowires with average diameter of 30nm and the uniform distribution on the surface of Ti3C2Tx nanosheets. Compare to Ti3C2Tx nanosheets, the average friction coefficient and wear scar width of the oil containing potassium titanate-Ti3C2Tx nanocomposites are decreased by 4.9% and 22% under the same conditions. The excellent tribological performance is attributed to the synergic effects of the two components in the nanocomposite structure.
Irradiation is a good modification technique, which can be used to modify the electrical properties, mechanical properties, and thermal properties of polymer materials. The effects of irradiation on ...the electrical properties, mechanical properties, and structure of polyimide (PI) films were studied. PI films were irradiated by a 1 MeV electron, 3 MeV proton, 10 MeV proton, and 25 MeV carbon ion. Dielectric constant, dielectric loss, and resistance measurements were carried out to evaluate the changes in the electrical properties; moreover, the mechanical properties of the pristine and irradiated PI were analyzed by the tensile testing system. The irradiation induced chemical bonds and free radicals changes of the PI films were confirmed by the Fourier transform infrared (FTIR) spectra, X-ray photoelectron spectroscopy (XPS), and electron paramagnetic resonance (EPR). The dielectric constant of the PI films decreases with the increase of fluences by the four kinds of irradiation sources.
Low temperature tension behavior of an Mg–3Al–1Zn alloy is evaluated at the strain rates of 10−2/s, 10−3/s and 10−4/s, respectively. Within a test temperature range from 300K to 77K, the work ...hardening behavior and strain rate sensitivity of the examined alloy are characterized to reveal the plastic deformation mechanism varying with temperature from the point view of dislocation motion. With the observation of high initial work-hardening rate, high strain rate sensitivity and low activation volume at cryogenic temperatures, the dominated mechanism of dislocation motion is regarded as varying from dislocation interacting with forest dislocation above 173K, into overcoming lattice fraction below 173K, especially when deformed at 77K.
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•Low temperature deformation characters of Mg-3Al-1Zn alloy was investigated.•Deformation mechanism transition at low temperature was found to occur around 173K for Mg-3Al-1Zn alloy.•Dislocation interaction with lattice resistance was considered as main source for WH and SRS change below 173K.
Polyether ether ketone (PEEK) films irradiated with 170 keV protons were calculated by the stopping and ranges of ions in matter (SRIM) software. The results showed that the damage caused by 170 keV ...protons was only several microns of the PEEK surface, and the ionization absorbed dose and displacement absorbed dose were calculated. The surface morphology and roughness of PEEK after proton irradiation were studied by atomic force microscope (AFM). GISAXS was used to analyze the surface structural information of the pristine and irradiated PEEK. The experimental results showed that near the surface of the pristine and irradiated PEEK exists a peak, and the peak gradually disappeared with the increasing of the angles of incidence and the peak changed after irradiation, which implies the 170 keV protons have an effect on PEEK structure. The influences of PEEK irradiated with protons on the melting temperature and crystallization temperature was investigated by differential scanning calorimetry (DSC). The DSC results showed that the crystallinity of the polymer after irradiation decreased. The structure and content of free radicals of pristine and irradiated PEEK were studied by Fourier transform infrared spectroscopy (FTIR) and electron paramagnetic resonance (EPR). The stress and strain test results showed that the yield strength of the PEEK irradiated with 5 × 1015 p/cm2 and 1 × 1016 p/cm2 was higher than the pristine, but the elongation at break of the PEEK irradiated with 5 × 1015 p/cm2 and 1 × 1016 p/cm2 decreased obviously.
The highly exfoliated Ti
3
C
2
T
x
nanosheets were synthesized by selective etching of the starting material of Ti
3
AlC
2
using 40 % concentrated HF solution at 65 °C for 5 h. The effect of HF ...treatment temperature on the exfoliation degree was investigated by characterizing the morphology and microstructure of the Ti
3
C
2
T
x
nanosheets using SEM, XRD, and TEM. The results showed that the exfoliation degree of Ti
3
C
2
T
x
was increased with increasing temperature. The role of the termination groups produced during HF treatment on the exfoliation degree was discussed. The tribological property of the prepared Ti
3
C
2
T
x
nanosheets as additives in PAO8 base oil was measured. The maximum reduction of friction and wear was achieved under additive concentration of 0.8 wt% for the highly exfoliated Ti
3
C
2
T
x
nanosheets. The different effects of Ti
3
C
2
T
x
additives on the average friction coefficient and wear volume were analyzed, respectively.
In recent years, the rapid development of portable equipment and flexible wearable devices urgently requires supercapacitor electrode material with high volumetric capacitance. Ti3C2Tx, a member of ...MXenes family, is one of the most promising supercapacitor electrode material candidates. However, how to further enhance the volumetric capacitance of the Ti3C2Tx is still a great challenge at present. In this paper, a simple and eco-friendly method is presented by preparing flexible Ti3C2Tx supercapacitor electrode using self-assembly of few-layer Ti3C2Tx followed by alkalinizing and annealing treatment. The alkalinized and annealed Ti3C2Tx film (denoted as ak-Ti3C2Tx film-A) exhibits an ultrahigh volumetric capacitance of 1805 F cm−3 at 1 A g−1, and an impressive cycling stability up to 98% capacitance retention after 8000 cycles. The significant improvement in volumetric capacitance performance is mainly due to the increase of redox-active sites exposed by removal of surface terminal groups during alkalinizing and annealing, and the enhancement in conductivity of the film owing to the annealing induced increase of crystalline order. Moreover, the supercapacitor fabricated with ak-Ti3C2Tx film-A displays an outstanding volumetric energy density of 45.2 Wh L−1. This work provides a new strategy for design and development of other MXenes-based materials with high volumetric capacitance performance for flexible and highly integrated supercapacitors.
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•ak-Ti3C2Tx film-A by using self-assembly of Ti3C2Tx followed by alkalinizing and annealing treatment is presented.•ak-Ti3C2Tx film-A show a significant enhancement in volumetric capacitance performance.•The symmetric supercapacitor fabricated with ak-Ti3C2Tx films-A displays an ultrahigh volumetric energy density.
MXenes is one of the most promising flexible electrode materials for supercapacitor. However, the nanosheets in the MXenes electrode by vacuum filtration are prone to restack during preparation, ...which largely hinders the full utilization of their surfaces and active sites. In this contribution, the self-restacking of MXene nanosheets (prepared by etching with HCl + LiF) could be prevented effectively by introducing MXene nanoparticles (prepared by etching with HF) as interlayer spacers. The Ti3C2Tx-10 flexible (the electrode with 10% mass fraction nanoparticles) exhibits an excellent specific capacitance of 372 F g−1 at 1 A g−1 which is much higher than that of Ti3C2Tx film, and an impressive cycling stability up to 95% capacitance retention after 5000 cycles. The significant improvement in electrochemical performance is mainly due to that the open sandwich-like structure of the flexible electrode based on multi-scaled Ti3C2Tx provides huge surface area and more active sites.
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•Flexible electrode based on multi-scaled MXene by using self-assembly of Ti3C2Tx nanosheets and nanoparticles.•Open sandwich-like structure of flexible electrode provides huge surface area and more active sites.•The flexible electrode show a significant enhancement in electrochemical performance.
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