No abstract

Damage induced in polymer composites by various impacts must be evaluated to predict a component’s post-impact strength and residual lifetime, especially when impacts occur in structures related to human safety (in aircraft, for example). X-ray tomography is the conventional standard to study an internal structure with high resolution. However, it is of little use when the impacted area cannot be extracted from a structure. In addition, X-ray tomography is expensive and time-consuming. Recently, we have demonstrated that a kHz-rate laser-ultrasound (LU) scanner is very efficient both for locating large defects and evaluating the material structure. Here, we show that high-quality images of damage produced by the LU scanner in impacted carbon-fiber reinforced polymer (CFRP) composites are similar to those produced by X-ray tomograms; but they can be obtained with only single-sided access to the object under study. Potentially, the LU method can be applied to large components in-situ.

No abstract

A unit for electrospinning of polymer melts was created. Nonwovens with an average fi bre diameter of 0.5-20 m were obtained from a melt of both pure polyamide 6 and its blends with stearic acid and oleic acid additives in the amount of 2-10 wt. % were obtained. Addition of 10% SF decreases the average diameter of the fi bres obtained by 40 times due to a decrease in the viscosity of the melt by 60 times.Electrospinning is a process for manufacturing ultrathin fi bres from polymer solution or melt under the effect of electrostatic forces. Electrohydrodynamic spraying of liquids (discovered for the fi rst time in 1745 by G. M. Bose [1]), where a weakly conducting liquid fl owing out of a nozzle under high voltage is sprayed into very fi ne drops by repulsive forces that are gradually precipitated on the opposite electrode, is the precursor of electrospinning. Patents for production of fi bre materials by electrospinning from solution were issued to Morton in 1902 in the USA for the fi rst time [2], but a major jump in the development of the solution method occurred in 1938 when I. V. Petryanov-Sokolov and N. D. Rozenblyum, colleagues at the L. Ya. Karpov Moscow Scientifi c-Research Institute of Physical Chemistry, in an attempt to obtain nitrocellulose aerosol from solution in acetone by electrohydrodynamic spraying, unexpectedly ran up against the competing regime of electrospinning of fi bres. Knowing how to evaluate the potential of this discovery, they could implement it in industry relatively rapidly.Fibres were probably obtained from polymer melts by the electrospinning method for the fi rst time in 1981 and described by Larondo and Manley [1]. They manufactured fi bres from polyethylene "solution-melt" in paraffi n and, more importantly, from pure polypropylene melt. The distance to the takeup plate was 1-3 cm, which allowed using an electric fi eld potential of approximately 7 kV without breakthrough of air. The fi bre diameter was greater than 50 m. It was then noted that the size of the fi bres obtained can be controlled by regulating the melt temperature and applied voltage. In addition, it was found that the viscosity is the most important parameter in production of fi bres from polymer melts than from solutions.The electrospinning process has many features. First, the one-time character of conducting all stages, so that a ready-to-use product is obtained at the end. Second, the universality of the method, which provides a broad spectrum of materials. Third, the fl exibility of the method, which allows controlling the structure of the materials. This is why the interest in production of polymer fi bres by electrospinning has now increased sharply.Despite the fact that most of the studies and manufacturing processes were executed for electrospinning of polymer solutions, spinning from polymer melts has a number of advantages.Many polymers (poly(ethylene terephthalate), polyolefi ns, some polyamides) are only soluble in scarce and expensive solvents at high temperature. This limits the use of these pol...

On the use of optical fiber Bragg grating (FBG) sensor technology for strain modal analysis AIP Conference Proceedings 1600, 39 (2014) Abstract. Adhesive bonding is being increasingly employed in many applications as it offers possibility of lightweighting and efficient multi-material joining along with reduction in time and cost of manufacturing. However, failure initiation and progression in critical components like joints, specifically in fatigue loading is not well understood, which necessitates reliable NDE and SHM techniques to ensure structural integrity. In this work, concurrent guided wave (GW) and fiber Bragg grating (FBG) sensor measurements were used to monitor fatigue damage in adhesively bonded composite lap-joints. In the present set-up, one FBG sensor was strategically embedded in the adhesive bond-line of a lapjoint, while two other FBGs were bonded on the surface of the adherends. Full spectral responses of FBG sensors were collected and compared at specific intervals of fatigue loading. In parallel, guided waves were actuated and sensed using PZT wafers mounted on the composite adherends. Experimental results demonstrated that time-of-flight (ToF) of the fundamental modes transmitted through the bond-line and spectral response of FBG sensors were sensitive to fatigue loading and damage. Combination of guided wave and FBG measurements provided the desired redundancy and synergy in the data to evaluate the degradation in bond-line properties. Measurements taken in the presence of continuously applied load replicated the in-situ/service conditions. The approach shows promise in understanding the behavior of bonded joints subjected to complex loading.