1,720,966 research outputs found
Elastoplastic Behaviour of Composite Laminates
No full textDuctile matrix composites undergo plastic deformation even at low stress levels. In this paper the elastoplastic behaviour of APC2 (AS4/PEEK) laminas is studied by means of a one-parameter plastic potential. The extension to laminates of constitutive relations that are based on this yield function is examined; a comparison is made between experimental data and numerical results obtained by integrating the elastoplastic relations for various stacking sequences monotonically loaded. Results are also shown regarding notched strength prediction of angle-ply laminates with a circular hole, based on an elastoplastic behaviour assumption
Elastoplastic Notch Factors and Strength of Graphite-Peek Laminates with a Circular Hole
No full textUltrasonic evaluation of matrix damage in impacted composite laminates
No full textConventional ultrasonic inspection methods are largely used for detection of delaminations in composite materials while only recently new techniques have been proposed to identify matrix cracks in simple tension loaded coupon specimens. In this study delaminations and matrix cracking caused by low-energy impacts on quasi-isotropic carbon/PEEK laminated plates are examined by means of different pulse-echo techniques: conventional time-of-flight and amplitude C-scans at normal incidence an used to check for the presence of delaminations, while backscattering C-scans tin which the transducer is set at an angle to the laminate plane) allow the detection of matrix cracks through the laminate thickness. Selected results from full waveform ultrasonic analysis of impacted carbon/PEEK laminates are discussed and compared with X-ray data in order to demonstrate the efficiency of the proposed inspection technique
Static and low frequency evaluation of a thin-film contact force sensor
No full textService robots meant for human interaction need to simulate touch sensitivity, or contact force is to be known for control purposes. Measurements have thus to be quick, reliable and have a good frequency response in the required band. Moreover, minimal dimensions are required, as well as an evenly responsive contact surface. We chose a commercial contact force sensor which exhibits all of these features: minimal overall dimensions, uniform measuring area, customizable range and certified linearity, no drift and hysteresis or good frequency response features. We present here our static and dynamic calibration results along with peculiarities we came across. We wanted to assess if the sensors would exhibit linear behaviour, no drift nor hysteresis as stated by the manufacturer. The sensors should offer uniform sensitivity over the sensing area, so matching section weights can be used to load them for static calibration. Besides this simple method, we also used hydrostatic pressure in a sealed chamber, getting rid of errors uncertainties coming from loading over the edges or from point loading. This method also allows for dynamic testing, as impulse loading or different frequency pressure waves can be applied to the sensors. Calibration curves will be presented in different loading conditions, focusing our attention on loading velocity and frequency. Although sensor gain exhibits remarkable changes after repeated loading, its smooth and continuous output make us think it can still be put in a feedback chain
An Instrumented Drop Weight Machine for Low Velocity Impact Testing
No full textIn this paper the design and development of an instrumented drop-weight machine for low velocity impact testing is presented; monitoring impact force history allows us to identify the different stages of damage progression and to correlate energy loss with damage extension. Results of tests on specimens of different materials and layups are presented and some data interpretation problems related to the use of various force transducers are discussed in order to evaluate the performance of the testing apparatus and its effectiveness in detecting onset and propagation of damage
Development of an instrumented drop weight machine for impact testing of composite materials
No full textAn Inflatable Pneumatic System For Blood Pressure Recovery
No full textIn this article a calf-plantar sequential pneumatic compression innovative device, consisting of three sensorized and PLC-controlled chambers, is designed and implemented. It performs a massage on the calf surface and on the foot sole at a given controlled pressure level and frequency and, in addition, carries out the ankle passive movement. Preliminary tests were performed on patients, using a commercial apparatus normally devoted to lymphatic drainage massage. In testing the mechatronic apparatus under real working conditions three air pressure transducers are used to feedback control the actuation system and the pressure trends in the actuator chambers during massage are here reported
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