ABSTRACT
"Interleaving" is widely used for interlaminar toughening of fiber-reinforced composites, and the structure of interleaving is one of the important factors affecting the toughening efficiency of laminates. Several experiments have demonstrated that compared to continuous and dense structures, toughening layers with structural heterogeneity can trigger multiple toughening mechanisms and have better toughening effects. On this basis, this work further investigates the application of heterogeneous toughening phases in interlaminar toughening of bidirectional GFRP. CNT was selected to construct toughening phases, which was introduced into the interlaminar of composites through efficient spraying methods. By controlling the amount of CNT, various structures of CNT toughening layers were obtained. The fracture toughness of modified laminates was tested, and their toughening mechanism was analyzed based on fracture surface observation. The results indicate that the optimal CNT usage (0.5 gsm) can increase the initial and extended values of interlayer fracture toughness by 136.0% and 82.0%, respectively. The solvent acetone sprayed with CNT can dissolve and re-precipitate a portion of the sizing agent on the surface of the fibers, which improves the bonding of the fibers to the resin. More importantly, larger discrete particles are formed between the layers, guiding the cracks to deflect in the orientation of the toughened layer. This generates additional energy dissipation and ultimately presents an optimal toughening effect.
ABSTRACT
Carbon fiber reinforced polymer composites have the advantages of being lightweight, having high strength and designability, and having been extensively used. However, the interlaminar toughness and delamination resistance of these composites are relatively poor due to their laminated structure and intrinsic brittleness of resin matrix. In this paper, commercialized free-standing carbon nanotube (CNT) films, drawn from CNT forests, were used to toughen the interlaminar interfaces of the composites. The effects of resin infiltration state and thickness of CNT films on the interlaminar toughening effect were systematically investigated. The results show that the pre-infiltration treatment of CNT films with acetone diluted epoxy resin solution can effectively improve the degree of resin infiltration. Compared with the samples containing untreated CNT film, the Mode I and Mode II interlaminar fracture toughness of the treated samples were significantly improved. The GIC reached a maximum of 1412.42 J/m2 at a CNT film thickness of 5 µm, which was about 61.38% higher than that of the baseline. At a CNT film thickness of 15 µm, the GIIC reached a maximum value of 983.73 J/m2, approximately 67.58% higher than that of the baseline. The corresponding toughening mechanisms were also systematically analyzed.
ABSTRACT
Many stroke survivors' quality of life is impaired. Few studies of factors influencing their quality of life have been based on the factors tested by the short form 36 instrument. This study did so with 308 physically disabled stroke survivors in rural China. Principal components analysis was applied to refine the dimension structure of the short form 36 assessment, followed by backward multiple linear regression analysis to determine the independent factors influencing quality of life. The structure revealed differed from the generic structure in showing that the mental health and vitality dimensions are not unidimensional. Subjects who reported access to the outdoors as convenient demonstrated better quality of life in all dimensions. Those who exercised regularly achieved better social functioning and negative mental health scores. Other factors influencing a better quality of life in terms of physical functioning were younger age and not being married. Being older and better educated predicted better role-emotion scores. Being female correlated with better social functioning scores, while men scored better on bodily pain. Being less educated predicted higher negative mental health, while being less disabled predicted better physical and social functioning. The results suggest that the SF-36's dimension structure should be re-evaluated before using it to assess stroke survivors.
ABSTRACT
BACKGROUND: There is compelling evidence of beneficial effects of non-immersive virtual reality (VR)-based intervention in the rehabilitation of patients with stroke, whereby patients experience both the real world and the virtual environment. However, to date, research on immersive VR-based rehabilitation is minimal. This study aims to design a randomized controlled trial to assess the effectiveness of immersive VR-based upper extremity rehabilitation in patients with subacute stroke and explore the underlying brain mechanisms of immersive VR-based rehabilitation. METHODS: Subjects (n = 60) with subacute stroke (defined as more than 1 week and less than 12 weeks after stroke onset) will be recruited to participate in a single-blinded, randomized controlled trial. Subjects will be randomized 1:1 to either (1) an experimental intervention group, or (2) a conventional group (control). Over a 3-week time period immediately following baseline assessments and randomization, subjects in the experimental group will receive both immersive VR and conventional rehabilitation, while those in the control group will receive conventional rehabilitation only. During the rehabilitation period and over the following 12 weeks, upper extremity function, cognitive function, mental status, and daily living activity performance will be evaluated in the form of questionnaires. To trace brain reorganization in which upper extremity functions previously performed by ischemic-related brain areas are assumed by other brain areas, subjects will have brain scans immediately following enrollment but before randomization, immediately following the conclusion of rehabilitation, and 12 weeks after rehabilitation has concluded. DISCUSSION: Effectiveness is assessed by evaluating motor improvement using the arm motor section of the Fugl-Meyer assessment. The study utilizes a cutting-edge brain neuroimaging approach to longitudinally trace the effectiveness of both VR-based and conventional training on stroke rehabilitation, which will hopefully describe the effects of the brain mechanisms of the intervention on recovery from stroke. Findings from the trial will greatly contribute to evidence on the use of immersive-VR-based training for stroke rehabilitation. TRIAL REGISTRATION: ClinicalTrials.gov, NCT03086889 . Registered on March 22, 2017.
