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Variable Angle Tow placement is a way to steer individual curvilinear fibers. This work presents the assessment of tensile behavior of open-hole composite laminates with Variable Angle Tow reinforcement. A new multi-scale finite element method, consisting of a microscale unit cell model and a macroscale gradient property model, is developed to simulate Variable Angle Tow structures with various fiber trajectories. The tensile strength and the failure process of open-hole reinforced laminates with Variable Angle Tow reinforcement under tensile loading are predicted and analyzed. Experiments are also conducted to investigate reinforcing efficiency and failure modes of the open-hole laminates. The comparison of predicted and experimental results for the tensile strength and failure modes of T700/Epoxy laminates demonstrates clearly that the mechanical behavior of Variable Angle Tow structure can be simulated very well by the proposed multi-scale model. Moreover, it is found that the tensile strength of Variable Angle Tow laminates is closely related to the eccentricity and it reaches the maximum value only when the trajectories of curvilinear fibers keeps consistent with maximum principal stress trajectories of the open-hole plate.

In this paper, the manufacturing and mechanical properties of steel-carbon fiber reinforced polymer (CFRP) hybrid composites were investigated. Steel-CFRP hybrid composites with different manufacturing processes were prepared to obtain different shear strength based on steel surface treatment (abrasion and grit blasting) and adhesive-bonding process. Single lap shear tests reveal that the steel/CFRP adhesion property can be improved by using grit blasting surface treatment on steel and introducing an adhesive layer at the interface. The steel/CFRP adhesion has no significant effect on the tensile and flexural properties of the hybrid composites, while the steel/CFRP interface failure occurs during interlaminar shear tests.

Subsurface damage (SSD) generated in rotary ultrasonic machining (RUM) process significantly deteriorates the technological and structural performance of the optical components. However, the invisibility of subsurface cracks underneath the machined surface makes it difficult to accurately and online evaluate the SSD depth. In the present research, incorporated with the probability statistics of the abrasive heights and the indentation fracture mechanics of the brittle material, a theoretical prediction model was established by investigating the inherent correlation between the measured cutting force of the diamond tool and the maximum depth of the subsurface cracks. Utilizing this predictive method, the SSD depth could be rapidly and precisely calculated through the mechanical properties of the material, the cutting force of the diamond tool, and the geometrical characteristics of the abrasives. To validate the feasibility of prediction technique, the experimental measurements of the maximum SSD depths were compared with the predicted results, revealing the acceptable consistency in their values.

Interfacial fracture toughness of co-cured steel-carbon fiber reinforced plastic (CFRP) hybrid composites were investigated in this paper. To illustrate the effect of the interlayer on the fracture toughness, steel-CFRP hybrid composites were prepared by different manufacturing processes based on steel surface treatment (abrasion or grit blasting) and adhesive-bonding process. The experimental results of double cantilever beam (DCB) tests and end notched flexure (ENF) tests demonstrate that, the Mode I and Mode II interfacial fracture toughness of the hybrid composites can be improved by using a grit blasting surface treatment on steel and introducing an adhesive layer at the steel/CFRP interface. The hybrid composites mainly show fiber/epoxy interfacial failure of CFRP under Mode I loading conditions, while it mostly exhibits adhesive failure of steel/CFRP interface under Mode II loading condition. Moreover, the interfacial tensile strengths of steel-CFRP hybrid composites are predicted by finite element analysis, and both experimental and numerical results confirm the improvement of interfacial fracture toughness.

This investigation represented a fundamental research on the potential effects of the high-frequency vibration on the hole integrity involved in rotary ultrasonic drilling (RUD) of carbon fiber-reinforced plastic (CFRP) composites. It was found the increased thickness of the CFRP plate shrunk the flowing velocity of the coolant, which brought about the residual chippings gradually accumulated at the radial clearance between the tool and the material. Furthermore, the chipping accumulation at the clearance seriously increased the friction effects and the resultant thermal load, thus leading to the chipping adhesions on the tool surface and machined cylinder jamming at the central hole of the tool. The mutual constrain between two vertical bundles brought the delamination around the holes generated in conventional drilling (CD) process to a termination at the bundle interface. The ultrasonic superimposition reduced the thrust force of the diamond tool which provided inadequate energy for the delaminated fibers reaching the bundle interface. Moreover, hole position on the two-dimensional orthogonal fabrics significantly influenced the propagation of the delaminated fibers, which weakened the effects of the drilling parameters on the delamination dimensions. Additionally, superimposing an ultrasonic vibration prolonged the abrasive trajectories and increased their overlapping probability, and the induced smoothing effects resulted in the obvious reduction of the surface roughness. The tensile stress exerted on the margin of the machined surface was responsible for the initiation of the CD delamination. After the delaminated fibers reached the bundle interface, the further extrusion of tool brought about the margin suffered from the shear stress, thus leading to the collapse of the machined cylinder. Considering the thrust force of the diamond tool and the undrilled thickness of the machined surface, the critical conditions of the delamination initiation were developed, which revealing that the decreasing of the thrust force caused the reduction of the critical undrilled thickness.

The cyclomatrix-type polyphosphazene is hypothesized to have potential as optical material due to the existing of transparent P=N ring skeleton. However, as an insoluble and infusible cross-linked polymer, cyclomatrix-type polyphosphazene is very difficult to be processed into film coatings. Herein, we reported a facile in situ template method to prepare cyclomatrix-type polyphosphazene optical film coating based on in situ polymerization between chlorocyclophosphazene and 4,4’-oxydianiline. A transparent coating with smooth surface and a translucent coating with uneven surface were successfully obtained by controlling reaction time. Their molecular structures, surface morphologies and topographies, cross-section morphologies, optical properties and preparation mechanisms were studied, respectively. As expected, the novel film coatings had good transmission in the visible region, especially the smooth transparent coating, which exhibited high transmittance (80 ∼ 90%). Moreover, the coatings unexpectedly exhibited UV-shielding capacity, especially the uneven translucent coating, which blocked the vast majority of UVA radiation (78.6%) and almost all of UVB radiation (99.8%). In addition, the possible preparation mechanisms of two coatings were also discussed. The primary stage of polymerization was dominated by a film-forming process based on template self-assembly, leading to smooth transparent film coating. As polymerization progress, many cyclomatrix-type polyphosphazene microspheres were produced by a forming-microsphere process and then deposited on the film surface, forming uneven translucent coating.