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Classical molecular dynamic simulations are performed to investigate the microscopic properties of hexadecyltrimethylammonium (HDTMA) intercalated smectites with and without the cointercalation of acetate groups. Three model smectites with distinct layer-charge characteristics are selected as the frameworks and their HDTMA intercalates correspond to the representative monolayer, bilayer, and paraffin configurations of the aliphatic chains. In the organoclays without cointercalation, all trimethylammonium headgroups of HDTMA are fixed firmly above the center of the surface six-member rings through electrostatic attractions with surface oxygen, whereas the alkyl chains are a little more mobile. It is found that the cointercalations can significantly increase the basal spacings of the pure HDTMA intercalated smectites. The distributions and mobility of the HDTMA headgroups are not affected by the acetate ions because of the overwhelming attractions coming from the clay sheets. The acetate groups are fixed by the HDTMA headgroups through ion pairing. This simulation study provides a molecular level basis to understand the effects of cointercalation on properties of organoclays. Keywords: HDTMA, acetate, molecular dynamic, smectite, cointercalation

The application of composite materials is an important measure to reduce the automotive wheel's weight. In order to ensure the safety of passengers, the wheels must pass a series of tests including the 13° impact test. For an injection-molded wheel, its production process has an influence on the material properties and residual stress distribution, which affect the wheel's mechanical performance. In this paper, the residual stress is introduced to analyze its effect on the impact resistance of composite wheels made of long glass fiber reinforced thermoplastic. First, to obtain the material properties, the specimens are subjected to the tensile test. Based on the test data, the properties including failure parameters can be obtained by reverse engineering. Next, the in-cavity residual stress can be obtained by mold flow simulation, after simulating the relaxation of residual stress during demolding process, the residual stress is introduced to the 13° impact test model. Last, the simulation and corresponding tests with different impact velocities are carried out. The results illustrate that the fracture of the wheel can be accurately simulated by using the simulation method, and the residual stress generated by injection molding process has little effect on the response or damage of the wheel. Considering the calculation efficiency, it is unnecessary to introduce the residual stress when simulating the performance of composite wheel under 13° impact load. This method can also provide an effective reference for subsequent design and simulation for composite wheels. [ABSTRACT FROM AUTHOR]

Squealing is a major matter of concern for environmental issues and the raised expectations for superior performances in braking systems. Squealing, as well as other types of noise nuisances, contributes to noise pollution and leads to additional expenses for phonic isolation. Brake squeal noise, which is defined as noise at frequency higher than 1000 Hz, occurs if the system has very high amplitude of mechanical vibration with sound pressure level above 80 dB. It involves instable vibrations, which are quite well understood as a result of mode couplings between the rubbing parts. These mode couplings are allowed by modal frequency shifts induced by the changes of sliding contact conditions. Nonetheless, the origin of squeal occurrence remains misunderstood as many parameters have to be taken into account, making it virtually impossible to predict when a squeal noise will appear or disappear. The strong coupling between structure and material, the continual change of the materials surfaces (chemistry and morphology), the influence of external parameters (temperature, pressure, hygrometry) all play a role in squealing. As a consequence, research on squealing is empirical by nature. Following this, one of the main goals in braking sciences is to determine the set of conditions on the parameters that provoke the start or the end of a squealing noise.

[Display omitted] • A G s measurement method based on the flow-around principle was proposed. • The mathematical model of the signal transformation process was established. • The measurement uncertainty of the device was evaluated less than 2.0 %. • The measurement device was semi-quantitatively verified by the industrial test. The solid circulation rate (G s) is a key parameter for the design and operation of a circulating fluidized bed (CFB) industrial equipment, while the detection and measurement of the G s value in an actual industrial CFB equipment remains difficult. To fill this gap, a method for the G s measurement based on the flow-around principle was proposed in this study. The mathematical model for the signal transformation was established along the path "detected strain value – impact force – particle velocity – G s value", and the corresponding measurement device was also developed. The performance of the G s measurement device was quantitatively validated in cold-state experiments and semi-quantitatively verified in an industrial trial in a CFB boiler. The results of a theoretical analysis indicate that the detected strain linearly increased with the impact force received by the intrusive spherical obstacle, and the slope coefficient was determined as per the experiment. The correlation of the impact force to the particle flow velocity was proposed and fitted using the experimental data. The computational particle fluid dynamics method was applied to simulate the particle flow field in the standpipe of the CFB boiler to determine the installation location of the G s measurement device. The lab-scale cold-state experiments showed that the relative standard uncertainty of the G s measurement using the device built in the present study was less than 2.0 %. This device was then applied in an industrial trial in a 116 MW th CFB boiler and the results proved the feasibility and applicability of the proposed G s measurement method. [ABSTRACT FROM AUTHOR]