Papers by Rafael Traldi Moura
International Journal of Impact Engineering, Mar 1, 2023
Machines, Mar 30, 2022
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
Journal of the Brazilian Society of Mechanical Sciences and Engineering, 2022
2018 40th Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC), 2018
This paper presents a method to estimate the elbow joint angle from surface electromyography (sEM... more This paper presents a method to estimate the elbow joint angle from surface electromyography (sEMG) measurements of biceps, triceps and brachioradialis. This estimation is of major importance for the design of human robot interfaces based on sEMG. It is also relevant to model the muscular system and to design biomimetic mechanisms. However, the processing and interpretation of electromyographic signals is challenging due to nonlinearities, unmodeled muscle dynamics, noise and interferences. In order to determine an estimation model and a calibration procedure for the model parameters, a set of experiments were carried out with six subjects. The experiments consisted of series of continuous (cyclical) and discrete elbow flexo-extensions with three different loads (i.e. 0 kg, 1.5kg and 3 kg). The sEMG data from the biceps brachii, triceps brachii and brachioradialis and the joint angle were recorded. Four different modeling techniques were evaluated: State Space (SS), Autoregressive with Exogenous Input (ARX), Autoregressive Moving-Average with Exogenous Input (ARMAX), Autoregressive Integrated Moving-Average with Exogenous Input (ARIMAX). After the model was selected, a second experiment was performed in order to validate the estimation procedure. The results show a procedure to estimate the EMG-to-angle relation with high correlation and low meansquare- root errors with respect to the measured angle data.
Journal of Medical Engineering & Technology, 2020
Cerebral palsy (CP) describes a group of disorders of movement, posture and balance caused by a n... more Cerebral palsy (CP) describes a group of disorders of movement, posture and balance caused by a non-progressive brain injury in the immature brain. It is the most prevalent cause of chronic motor disability in childhood, and although two thirds of CP children are able to walk, they show gait limitations. In this context, rehabilitation therapy can improve muscle balance and gait. Previous studies showed the importance of gait analysis as part of multidisciplinary tools for effective rehabilitation treatment. However, the high cost and the infrastructure required for the implementation of commercial gait analysis systems as well as the time-consuming preparation procedures, limit the access to this service. A low cost, non-restrictive, portable and of simple operation and installation system was developed based on Kinect v2 sensor. This study aims to validate it for capturing and analysing gait parameters in children with cerebral palsy. Several gait parameters from eleven CP patients with different levels of disability classified as a function of the Gross Motor Function Classification System (GMFCS) from II to III were recorded while they walked on a flat surface. The Kinect-based gait analysis system was compared with videorecording that yielded the same results. These results show the potential of Kinect to analyse gait in frail patient populations unobtrusively and with very low cost. More importantly, regarding to spatial parameters, the Kinect system was useful even for the worst case of GMFCS III that show a large gait variability with abnormal patterns.
International Journal of Adhesion and Adhesives, 2019
The objective of this study was to evaluate the aging protocols and the specimen shape (sticks an... more The objective of this study was to evaluate the aging protocols and the specimen shape (sticks and dumbells) in the adhesive strength between dentin and resin composite during microtensile stress. The specimens were submitted to no aging protocol, mechanical cycling (using macro and micro-rotation methods), thermal cycling and micro-tensile test. The stress distribution for the two specimen shapes was performed by finite elements analysis. Data were submitted to 3-way ANOVA and Tukey Test (α=0.05). There is no statistical difference considering the interactions among the factors: specimen shape, thermal cycling, and mechanical cycling. Also, the mechanical cycling, for both methods, micro or macro-rotation, and the thermal cycling did not affect the adhesive strength of the samples. However, the specimen with the dumbbell shape showed higher adhesive strength (16±3 MPa) than the stick shape specimen (11±2 MPa). The stress distribution in dumbbell shape was more homogeneous than in the sticks. It can be concluded that the aging protocols tested were not enough to degrade the adhesive interface and the dumbbell shape specimen is better to predict the real adhesive strength developed in the interface.
Sensors (Basel, Switzerland), Jan 5, 2018
Carbon nanotube yarns are micron-scale fibers comprised by tens of thousands of carbon nanotubes ... more Carbon nanotube yarns are micron-scale fibers comprised by tens of thousands of carbon nanotubes in their cross section and exhibiting piezoresistive characteristics that can be tapped to sense strain. This paper presents the details of novel foil strain gauge sensor configurations comprising carbon nanotube yarn as the piezoresistive sensing element. The foil strain gauge sensors are designed using the results of parametric studies that maximize the sensitivity of the sensors to mechanical loading. The fabrication details of the strain gauge sensors that exhibit the highest sensitivity, based on the modeling results, are described including the materials and procedures used in the first prototypes. Details of the calibration of the foil strain gauge sensors are also provided and discussed in the context of their electromechanical characterization when bonded to metallic specimens. This characterization included studying their response under monotonic and cyclic mechanical loading. ...
International Journal of Crashworthiness, 2016
Abstract The main function of a road guardrail is to redirect an out of control vehicle avoiding ... more Abstract The main function of a road guardrail is to redirect an out of control vehicle avoiding a frontal collision or a dangerous veering off the road trajectory. Second, the energy absorption imposed by barrier deformation or any other energy dissipation method is beneficial to the car occupant safety. This study evaluates the performance of a W-Beam guardrail system, in accordance to Brazilian Standards, in respect to the kinetic energy absorption and to the vehicle return angle to the road. This evaluation of the guardrails is performed in a virtual environment using the finite element method. For the correct representation of the model, the material was characterised through experimental tests. Simplifications in the model are taken from the literature and a validated model of a vehicle is provided by the US National Crash Analysis Center.
2016 6th IEEE International Conference on Biomedical Robotics and Biomechatronics (BioRob), 2016
One of the key aspects in exoskeleton design for neurological rehabilitation is related to the de... more One of the key aspects in exoskeleton design for neurological rehabilitation is related to the definition of a certain dynamics that improves or accelerates the learning of a desired movement or a rehabilitation process. In order to assess the process of learning or adaptation of a coincident timing task, we have used an exoskeleton-based experiment applying different dynamics. The experimental task consisted of intercepting a moving virtual target displayed on the screen. The interception area was defined simultaneously in a virtual and a real environment. The real target was marked on a table, in such a way that the subject wearing the elbow exoskeleton could reach the target by performing an elbow flexion. The task goal was to position the hand over a marker placed on the table at the same time as the virtual object ascended to the virtual interception area on the computer screen. Hand motion data were acquired by an inertial sensor (VN-100, VectorNAv) attached to the subject's hand while electromyography (EMG, FreeEMG, BTS) was used to record the activity of the following muscles: biceps brachii, triceps brachii and brachioradialis to assess muscle response. Our research focused on the percentage of correct responses and the tendency of correct responses. We also monitored smoothness of the movement and correlated our observations with EMG activities. The preliminary results indicate that the addition of a mechanical predictable load improves the learning rate.
Dynamic compressive curves of high density semi-crystalline polyethylene, PEHD, were obtained via... more Dynamic compressive curves of high density semi-crystalline polyethylene, PEHD, were obtained via the Split Hopkinson Pressure Bar, SHPB, technique. The SHPB was fitted with polymeric bars, PMMA, to avoid a large impedance mismatch between the specimens and the bars. As a consequence, attenuation and dispersion had to be taken into account. Care was also exercised with frictional effects by using ring specimens instead of flat disks. Ring specimens have the additional advantage of yielding a more constant strain rate in the tests. The results clearly show a very strain rate sensitive material, a feature which should be taken into consideration when analysing PEHD components.
International Journal of Plasticity, 2015
Many engineering ductile materials, such as metals, show inelastic behavior with corresponding la... more Many engineering ductile materials, such as metals, show inelastic behavior with corresponding large deformations. For these materials, the prediction of failure, defined as local material separation, is still nowadays a scientific challenge. Failure initiation, its locus and evolution, has been discussed extensively in recent literature. This work presents a bifailure specimen, especially developed to evaluate failure criteria at high and low triaxiality. In order to explore further the failure phenomenon, uncoupled models are numerically implemented in an explicit finite element code. Simulations were performed and do indicate that, for the studied examples, uncoupled models are not capable of correctly predicting failure.
SAE Technical Paper Series, 2007
Dental Materials, 2011
Objectives: To evaluate, in demineralized dentin, the effect of chlorhexidine-CHX and MDPB on den... more Objectives: To evaluate, in demineralized dentin, the effect of chlorhexidine-CHX and MDPB on dentin/restoration bond strength (BS) after simultaneous thermo-mechanical cycling. Materials and methods: Cavities of demineralized bovine dentin (n = 10) were randomly assigned according to the adhesive system (Clearfil SE Bond-SE 1 ; Clearfil SE Protect-CP 2), dentin cleaning for 60 s with CHX 3 or not and cycling into 8 groups: G1-CP+CHX/24h, G2-CP−CHX/24 h, G3-SE+CHX/24 h, G4-SE−CHX/24 h, G5-CP+CHX/cycling, G6-CPCHX/cycling, G7-SE+CHX/cycling, G8-SE+CHX/cycling. Cavities were restored with composite and the specimens were submitted to thermo (500 cycles at 5 • C and 55 • C with a dwell time in each bath of 30 s) and mechanical degradation (100,000 cycles in wet environment, 4 Hz and 60 N) simultaneously, during the baths. The BS was evaluated by the push out test in a Universal Testing Machine (Instron) and the data were analyzed statistically using ANOVA and Tukey' tests (p < 0.05). The failure sites were evaluated by scanning electron microscopy (SEM), at 50× and 200× magnifications. Results: No significant interaction was observed between adhesive systems and cleaning procedure with CHX, however a significant interaction between the use of CHX and cycling was observed; before cycling, cleaning with CHX (14.25 MPa) produced higher bond strength than without CHX (9.87 MPa). After cycling, there was no significant difference between the groups with (12.19 MPa) and without CHX (13.52 MPa) cleaning. There was a predominance of mixed failures in groups 1, 2, 3, 5, 6 and 7, and adhesive failures in groups 4 and 8. Conclusions: It can be concluded that the use of CHX on cavity cleaning did not affect the longevity of bonding to dentin for the adhesive systems used.
Research, Society and Development, 2021
Introduction: Thermopolymerizable acrylic resins are widely used in dentistry because they have s... more Introduction: Thermopolymerizable acrylic resins are widely used in dentistry because they have several satisfactory properties. These materials tend to undergo changes in their structure during use, which can cause inflammation and infections. The most diverse researches sought to develop a way to reduce this possibility and Dos Santos in 2020 evidenced that this material added with the biocide poly (diallyl dimethylammonium chloride) has an antibacterial and antifungal potential, indicating this increase only for prostheses that do not suffer any type of force during its use. Objective: to show the behavior of the thermopolymerized acrylic resin plus poly (diallyl dimethylammonium chloride) against compression tests seeking to evaluate its behavior in this situation. Methods: The compression tests were carried out using the double-column Instron3369 universal testing machine in front of two groups; G1 being the material without the addition of the biocide and G2 the material with ...
2021 43rd Annual International Conference of the IEEE Engineering in Medicine & Biology Society (EMBC), 2021
Bioinspiration can be used to improve the efficiency of these assistive biomechatronic devices. I... more Bioinspiration can be used to improve the efficiency of these assistive biomechatronic devices. In this paper, a cable driven actuator for the human ankle was designed using a bioinspired approach. The torque reduction was achieved by means of force amplifying elements such as cables with pulley, and, to reduce the power requirements for the motor, the actuator mimics a muscle using a clutched parallel elastic element. The simulations to validate the model were performed using real gait data and the results prove the viability of the device to be used in anthropomorphic legs and exoskeletons. Although the losses due to friction were not considered, the simulations showed a reduction of 60% in the force peak and 40% in the power peak.
International Journal of Impact Engineering, 2010
This paper presents first material tests on HDPE and PVC, and subsequently impact tests on plates... more This paper presents first material tests on HDPE and PVC, and subsequently impact tests on plates made of the same materials. Finally, numerical simulations of the plate impact tests are compared with the experimental results. A rather comprehensive series of mechanical material tests were performed to disclose the behaviour of PVC and HDPE in tension and compression. Quasi-static tests were carried out at three rates in compression and two in tension. Digital image correlation, DIC, was used to measure the in-plane strains, revealing true stress-strain curves and allowing to analyze strain-rate sensitivity and isotropy of Poisson's ratio. In addition, dynamic compression tests were carried out in a split-Hopkinson pressure bar. Quasi-static and dynamic tests were also performed on clamped plates made of the same PVC and HDPE materials, using an optical technique to measure the full-field out-of-plane deformations. These tests, together with the material data, were used for comparative purposes of a finite element analysis. A reasonable agreement between experimental and numerical results was achieved.
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Papers by Rafael Traldi Moura