Long fiber thermoplastic (LFT) composites are processed either with extrusion compression or fiber injection processes. The properties of LFT materials are highly influenced by processing techniques, ...which lead to different porosity contents, fiber length distributions, and fiber orientation distributions. It is important to understand the various LFT processing techniques and their effects on mechanical, thermal, and microscopic properties. This work considered LFT sheets processed via extrusion, which offers highly aligned fibers (referred to as “Tecnogor composites”), and LFT composites produced via extrusion compression molding (ECM), which offers a random distribution of fibers. Tecnogor composites exhibited higher flexural strength (35–65%), flexural modulus (132–172%), tensile strength (39–52%), tensile modulus (67–75%), and Izod impact resistance (195–220%) than the random LFT composites. This response was attributed to the aligned fibers in Tecnogor composites. Mathematical models including Halpin-Tsai and Lavengood-Goettler were used to predict and compare the Young’s modulus of Tecnogor and ECM composites, respectively.
The integration of repurposed and recycled carbon fibers into high-performance composites is essential to the adoption of composites for automotive structures due to their low-cost, high formability, ...and reduced environmental impact. When high areal density nonwovens of these fibers are infused with a semi-crystalline thermoplastic resin, organosheets offering competitive mechanical properties can be produced. This study examined the optimization of such composites through multiscale material characterization and post-process annealing. Single fiber tensile tests were used to characterize repurposed and recycled fiber formats. The thermomechanical properties of the polyphenylene sulfide matrix and resulting composites subjected to different post-process annealing conditions were characterized using differential scanning calorimetry, dynamic mechanical analysis, and nano-indentation. Single fiber push-in testing was conducted to evaluate the fiber–matrix interface as a function of annealing. It was shown that statistical methods based on the bootstrap principle successfully identify the effects of post-process annealing, which are otherwise masked by material inhomogeneity. Post-process annealing was shown to be an effective method of improving the resulting mechanical properties of repurposed and recycled carbon fiber organosheet composites, thereby optimizing their properties for use as a high-performance automotive structural material.
Twenty Years of Mixture of Experts Yuksel, S. E.; Wilson, J. N.; Gader, P. D.
IEEE transaction on neural networks and learning systems,
08/2012, Letnik:
23, Številka:
8
Journal Article
In this paper, we provide a comprehensive survey of the mixture of experts (ME). We discuss the fundamental models for regression and classification and also their training with the ...expectation-maximization algorithm. We follow the discussion with improvements to the ME model and focus particularly on the mixtures of Gaussian process experts. We provide a review of the literature for other training methods, such as the alternative localized ME training, and cover the variational learning of ME in detail. In addition, we describe the model selection literature which encompasses finding the optimum number of experts, as well as the depth of the tree. We present the advances in ME in the classification area and present some issues concerning the classification model. We list the statistical properties of ME, discuss how the model has been modified over the years, compare ME to some popular algorithms, and list several applications. We conclude our survey with future directions and provide a list of publicly available datasets and a list of publicly available software that implement ME. Finally, we provide examples for regression and classification. We believe that the study described in this paper will provide quick access to the relevant literature for researchers and practitioners who would like to improve or use ME, and that it will stimulate further studies in ME.
Natural fibres are studied as alternatives for man-made fibres to reinforce composites while keeping the weight lower. The assessment of the value of some commonly available tropical fibres for the ...composite industry starts with the determination of the strength, E-modulus and strain to failure through single fibre tensile tests. The mean strength and standard deviation is calculated following the normal and Weibull distribution resulting in the questionable benefit of applying the Weibull distribution. Furthermore, a correction method assesses the real fibre elongation from the measured clamp displacement. This procedure seems to be useful for strong, brittle fibres to produce more reliable results for the E-modulus and strain to failure.
The aim of this work is to investigate the drilling behavior of multiple layer orthotropic polyester composite reinforced with woven polyester fiber and PTFE particle. Drilling ability of the ...synthetic polymer composite bearing material was examined using a drilling system with different drill bits, feed rate, and spindle speed parameters. The investigation was performed by changing the tool and composite interface. Drilling experiments were carried out on two orientations of the composite structure using three types of drill bits. Results show that the tribomechanical behavior of the drilling operation is affected at different levels by tool geometry and coating. This multiscale behavior is related to the intrinsic friction properties of tool design and coating nature that influence the tribologic contact at the interface between the cutting tool edge and composite surface. The ANOVA was used in the evaluation of experiment results. The best results of thrust force, torque, and surface roughness were obtained with HSS Co bit. Drilling of perpendicular direction requires lower thrust force and torque values than the parallel direction to fiber lamination.
•The thrust force and torque values of perpendicular direction (A) are smaller than the parallel direction (B).•In general, the thrust force increases with increasing feed rate and spindle speed.•The surface roughness results of drilling with CrV and HSS Co drill bits are independent of the drilling parameters but influenced in the case of using the HSS TiN.•The drilling with HSS TiN and HSS Co bits results with narrow affected zone, whereas CrV bit results with wide affected zone.•It is more advantageous to use the HSS Co drill bit where the lowest cutting forces were obtained at the drilling of the composite material.
In this paper, we propose a three-dimensional (3D) cluster-based model for the fifth generation (5G)/beyond 5G (B5G) vehicle-to-vehicle (V2V) massive multiple-input multiple-output (MIMO) wideband ...channels. It is the first cluster-based irregular shaped geometry-based stochastic model (IS-GBSM) to distinguish the dynamic clusters and static clusters in vehicular massive MIMO communication scenarios. This model not only considers the high time-variance, the time non-stationarity, and the vehicular traffic density (VTD) of V2V channels, but also models the massive MIMO channel characteristics, such as spherical wavefronts by 3D vector calculation and space non-stationarity. Meanwhile, this model for the first time integrates the VTD into birth-death process to model the channel characteristics of V2V and massive MIMO jointly and deeply, where a novel VTD-combined time-array cluster evolution algorithm for 5G/B5G V2V massive MIMO channel model is developed. Based on the proposed model, we derive some expressions of channel statistical properties, including time-space-frequency correlation function (STF-CF) and Doppler power spectral density (DPSD). The influence of several parameters, e.g., VTDs, vehicle moving directions, and antenna spacings, on the channel characteristics are sufficiently explored, which can provide assistance for the design of vehicular massive MIMO communication systems. Finally, the utility of the proposed model is verified by the close agreement between simulation results and measurement data.
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