In this study, a fiber Bragg grating (FBG) pressure sensor was designed and fabricated using 3D printing method for the measurement of vertical pressure. Raw material used for the fabrication of this new pressure sensor was Polylactic Acid (PLA). The effectiveness of embedding FBG sensors inside printed PLA material was first examined taking into account different infill densities. It is found that FBG sensor can be successfully embedded into PLA material without sacrificing its sensing performance. The change of infill density has no influence on both peak and residual wavelength change of FBG sensors during and after printing process. All FBG sensors printed inside PLA prototype with different infill density values exhibit almost the same peak and residual wavelength rise values in printing process. In addition, the higher the density value, the longer the time required to finish printing process. A simple FBG pressure sensor was designed and fabricated according to the successful experience of embedding FBG sensors into printed PLA. Measurement performance of this FBG pressure sensor was examined in laboratory cyclic loading tests. Calibration tests indicate that the maximum measured vertical pressure of this new pressure sensor was 2000 kPa with a measurement sensitivity of 13.22 kPa/pm.

In this study, 3D printing method and fiber Bragg grating (FBG) sensing technology were combined to fabricate a simple and small size tilt sensor. Raw material for creating different sensor components was Polylactic Acid (PLA) material. Bare FBG sensors were directly inscribed into PLA material using fused deposition modeling (FDM) process for a complete protection. Printing test using FDM process indicate that bare optical fiber cables successfully survived the FDM process even though the melted PLA materials approached a maximum temperature of around 220°. Two FBG sensors characterized by different wavelength values were symmetrically arranged inside a sensing unit for the measurement of tilt angle in terms of their wavelength shifts. The minimum resolution and measurement range of this new FBG tilt sensor were 0.084° and ± 75°, respectively. Measurement performance of this new tilt sensor was also verified with conventional tilt sensor. A small slope model was built up in laboratory to exam measurement performance of three FBG tilt sensors which were mounted at different depths inside the slope model. Measured horizontal displacement data from FBG tilt sensors were verified with the output data of Linear Variable Displacement Transducer (LVDT) and the obtained maximum error was less than 3% when the maximum displacements are approached.

This study proposed a new fiber Bragg grating-based smart ring for monitoring body joint postures occurred at elbow joint and knee joint positions. A single-mode fiber Bragg grating sensor was embedded into a 3D printed ring for sensing occurred deformation of the ring. The raw material used for fabricating the smart ring was polylactic acid, which was found to have the advantages of being flexible in nature and having ease of fabrication using fused deposition modeling method. The fabrication process of the fiber Bragg grating smart ring was characterized by the advantages of ease of handling, quick prototyping, high resolution, low cost, and time-saving. Bare fiber Bragg grating sensors were successfully embedded into hot printed polylactic acid material during the fused deposition modeling process, even the printing temperature of the printing nozzle exceeded 200℃. Two new smart wearable rings were fabricated and used to monitor systematic bend motion of elbow joint and knee joint. The measurement sensitivities of the two smart rings mounted at the elbow joint and knee joint were 0.0056 nm/° and 0.0276 nm/°, respectively. The corresponding maximum measurement angle within current calibration tests were 90° and 100°, respectively. The method of using both fiber Bragg grating and fused deposition modeling for sensor design can be extended for the fabrication of other sensors such as temperature sensors, strain sensors, pressure sensors, stress sensors, displacement sensors, and tilt sensors.

Smart wearable technology is exceedingly desirable in athletic sports due to being lightweight, flexible to bend, soft and comfortable. It can continuously deliver accurate information and deformation. During knee flexion, the upper knee perimeter increases with the shrinkage of the knee joint flexor, and it can be monitored. In this study, a fiber Bragg grating (FBG) smart belt is fabricated by embedding FBG sensors at the center of a special silica gel (with unique adhering characteristics to fix FBG on the surface of the belt) for sensing knee joint movements. Polyvinyl chloride strips were adhered to the surface of the smart wearable belt for better protection. The smart belt was calibrated in the laboratory by a systematical changing knee posture and used to identify body postures at various static and kinematic postures of a male subject. The FBG-based smart wearable belt presented a consistent wavelength change after each step by angle changes at the knee joint position. The wavelength increment of FBG sensors increases linearly with the increasing of the bend angle of the knee joint in static tests, and the related slope ratio was 0.3 nm/°. In a jogging test, the measurement sensitivity achieved by the FBG smart wearable belt was within a range between 0.018/° and 0.021 nm/° for the male subject at the velocities of 2 and 3 km/h, respectively. The smart wearable belt could be a useful index to characterize a simple design and ease of implementation, and could also applied for knee posture circumferential strain measurements, especially for sports activities and monitoring stroke patients. This FBG smart belt can be fabricated to produce smart sensing fabrics.

During the past few decades, soil nailing has been widely used for stabilizing slopes and excavations. The nail-soil interface shear resistance in the passive zone of a slope or excavation is a critical parameter in design. In this paper, an analytical study is proposed to investigate the progressive pullout response of a soil nail. Pullout process is divided into three typical phases: (1) the initial pure elastic phase during which the nail-soil interface follows a linear elastic stress-displacement relationship; (2) the elastic-plastic phase during which a transition point presents dividing the elastic and plastic zones; and (3) the final pure plastic phase. A comparison study between calculations and laboratory test data are presented to examine the effectiveness of the method. In addition, a comprehensive parametric study is performed to assess the effects of several key factors on the pullout resistance of a soil nail. These factors include the length and diameter, length of plastic zone, and...