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In this study, the formation of laminated composites based on PEEK plates and prepregs from carbon fiber (CF) fabric and the PEEK binder were investigated. The varying parameters were the prepreg thickness (and the binder content as a result), as well as the ultrasonic welding (UW) duration. Their optimization enabled to obtain a uniform structure in the fusion zone without any damages of the CF-fabric, causing improved strength properties. It was shown that the prepreg thickness determined its ability to melt upon the investigated UW durations. In the case of the thinnest prepreg of 280 µm with the minimal binder content, the homogeneous low-defect interface had been formed. However, its fracture occurred by the tear mechanism. In the case of the thicker 460 µm prepreg, the UW joint was able to maintain its integrity in the shear tests at the high stress level, while the UW joint failure was along the interface between the UW joint and the base material. At the maximum studied UW duration, the prepreg had been melted and the CF-fabric had been damaged, as well as a significant number of defects (pores) had been formed at the interface. This had caused the increased withstand stresses in the shear test due to the interface reinforcement, but the formation of such a structure is unacceptable in real products. Finally, options for practical implementations of the obtained results were discussed. [ABSTRACT FROM AUTHOR]

The paper presents the investigation results of fatigue behavior of three types of materials: (i) wrought Ti-6Al-4V, (ii) Ti-6Al-4V fabricated using selective laser melting and (iii) Ti-6Al-4V fabricated using selective laser melting (SLM) with subsequent post-build processing by Ultrasonic Impact Treatment (UIT). The deformation behavior and fracture pattern of the specimens under cyclic loading was studied by means of scanning electron microscopy of the fracture surfaces and digital image correlation (DIC). The results obtained show that the proposed technique for post-build treatment of SLM specimen increases their fatigue durability by ∼60%. Moreover, the latter tends to exceed the lifetime of wrought Ti-6Al-4V. SEM and DIC studies witness the increase in ductility of the post-build treated material, which is supported by more ductile fracture surface pattern and larger strain of the specimen during cyclic loading. [ABSTRACT FROM AUTHOR]

The paper deals with the investigation of ultrasonic impact post-build treatment of SLM-manufactured Ti-6Al-4V. SLM blanks were cut along building direction and subjected to ultrasonic impact surface treatment. Post-build treated specimens were tested by uniaxial tensile testing with in situ strain monitoring via digital image correlation technique (DIC), while the fracture surfaces were studied by scanning electron microscopy (SEM). The analysis of the experimental data allowed revealing the effect of post-build treatment on mechanical properties and on the peculiarities of deformation behavior. Analysis of SEM images of fracture surfaces allowed us to distinguish the differences between structure influence onto failure pattern both for the treated and non-treated specimens. [ABSTRACT FROM AUTHOR]

The paper presents the investigation of the grain structure of initial homogeneous aluminum alloy AA8090 and welded specimen using friction stir welding. An optical microscopic study reveals four zones in the welding seam. In order to evaluate deformation and fracture behavior, Charpy V-notch impact tests were performed with the recording of emitted acoustic signals (acoustic emission) and capturing of loading diagrams by the instrumented striker. The formation of a large area of grain boundaries in welded specimen leads to a significant increase in the energy required for the initiation and propagation of a crack under impact loading, while initial alloy demonstrates low impact toughness. Registered acoustic signal was further analyzed by means of wavelet spectrum. [ABSTRACT FROM AUTHOR]