External Fixtures Research Articles

Induction thermography for unidirectional CFRP composites: A novel inspection approach through global current path integration

In the evolving field of non-destructive testing of composite materials, induction thermography offers significant potential. However, its application to Unidirectional Carbon Fiber Reinforced Polymer (UD CFRP) composites remains challenging due to the unavailability of global current paths. This study introduces a novel methodology to inspect UD CFRP composites using Induction Thermography by incorporating an additional conduction current loop between the composite layers. Initial proof-of-concept experiments were conducted on fiber tow and further validated on laminates. The findings substantiate that the integration of a global current path notably facilitates laminate heating, enhancing the induction thermographic inspection capability. An unexpected discovery in our research is the ability of a circular coil to detect fiber breakage in a laminate that is nearly an order of magnitude wider than the coil diameter, thus demonstrating the approach’s high sensitivity. The practical applicability of the proposed methodology was demonstrated using an external fixture. Moreover, this work proposes an innovative modification to the manufacturing process of non-crimp textiles by incorporating a conductive thread, envisaged to bolster the induction thermographic inspection efficiency further. Numerical modeling, closely aligning with experimental observations, provides a robust theoretical foundation for our work.

Cohesive fracture measurement technique for free-hanging thin films using highly stressed superlayer

• Development of thin film cohesive fracture test method using highly stressed superlayer. • Test method does not require expensive test equipment or external fixtures or loads. • Test method uses standard fabrication processes that create representative films. • Cohesive fracture toughness of thin film silicon dioxide measured to be 8.9-14 J/m 2 . The cohesive fracture of thin films is a concern for the reliability of many devices in microelectronics, nano-electromechanical systems/micro-electromechanical systems, photovoltaics, and other applications. In microelectronics, cohesive fracture toughness has become a concern with new dielectric materials currently being used. To design against such cohesive cracking, it is necessary to experimentally measure the cohesive fracture properties of these thin films. Many of the current tests to measure the cohesive fracture toughness of thin films are based on methods developed for larger scale specimens. Here, a fixtureless method to measure the critical total energy release rate of thin films has been developed that utilizes photolithography fabrication processes and a thin film superlayer. The superlayer has a high intrinsic stress and is used to drive cohesive fracture in the test material that it is deposited on top of. This test method has been used here to measure the cohesive critical total energy release rate of a dielectric thin film of silicon dioxide with experimental samples of thicknesses ranging from ∼100 to 400 nm to be between 8.9 and 14 J/m 2 .

A Compact Broadband Transparent Waveguide Window Based on Low-Loss Cyclic Olefin Copolymer

The concept of compact waveguide window based on the low-loss cyclic olefin copolymer (COC) is proposed in this letter, which considers the characteristics of broadband performance, transparency, sufficient mechanical strength, and simple mechanical process, by simply integrating the machined bipyramids-type COC dielectrics into the modified waveguide. To verify our idea, two waveguide windows consisting of internal dielectrics and external fixtures are designed and fabricated. The two types of waveguide windows are measured along with two strain rectangular waveguides at the Ka -band with the return loss better than 18.5 dB over the related frequency range of 42.8% and better than 20 dB over the related frequency range of 49%, respectively. The measured results show the advantages of the proposed concept, which is an excellent candidate for broadband application at a millimeter-wave frequency or higher.

Numerical analysis of the influence of the damping rings' thickness on interrupted dynamic tension results using SiC-reinforced ZC71 magnesium alloy specimens

Abstract. This article discusses the influence of the thickness of the damping rings used for interrupting a dynamic tension experiments on the results of a modified split Hopkinson tension bar (SHTB). In this paper a device enclosed in an external fixture used for interrupting a dynamic tension experiment in a SHTB is studied. The novelty of this manuscript with respect to previous studies lies in the fact that the dynamic tension experiment in a SHTB is interrupted in order to study the mechanical behavior of the material at high strain rates. The role played by such device is to interrupt the experiment at different levels of plastic deformation, particularly when the specimen is about to reach its failure strength. Finite-element (FE) simulations of high-strain-rate tension experiments are accomplished on a particle-reinforced metal matrix composite specimen (namely SiC-reinforced ZC71 magnesium alloy) when varying the thickness of the damping rings. Interrupting the test before the specimen breaks offers the possibility of being able to study in a more detailed way the deformation process of such material at high strain rates. Therefore, this work focuses on the study of the behaviour of materials undergoing high strain rates, developing a tool which allows materials to withstand different levels of strain rates in a controlled manner and providing guidance for future studies. In view of this research, it can be concluded that the thickness of the damping rings is a factor that can resolutely influence the interrupted dynamic tension experiment results avoiding the specimen's failure by optimally buffering the experiment using 0.8 mm thick lead damping rings.

An experimental method to determine the intralaminar fracture toughness of high-strength carbon-fibre reinforced composite aerostructures

ABSTRACTCarbon fibres with high tensile strength are being increasingly utilised in the manufacture of advanced composite aerostructures. A Modified Compact Tension (MCT) specimen is often deployed to measure the longitudinal intralaminar fracture toughness but a high tensile strength often leads to premature damage away from the crack tip. We present an approach whereby the MCT specimen is supported by external fixtures to prevent premature damage. In addition, we have developed a novel measurement technique, based on the fibre failure strain and C-scanning, to determine the crack length in the presence of surface sublaminate delamination which masks the crack tip location. A set of cross-ply specimens, with a ((90/0)s)4layup, were manufactured from an IMS60/epoxy composite system Two different data reduction schemes, compliance calibration and the area method, are used to determine the fibre-dominated initiation and propagation intralaminar fracture toughness values. Propagation values of fracture toughness were measured at 774.9 ± 5.2% kJ/m2and 768.5 ± 4.1% kJ/m2, when using the compliance calibration method and the area method, respectively. Scanning Electron Microscopy (SEM) is carried out on the fracture surface to obtain insight into the damage mechanism of high-tensile-strength fibre-reinforced unidirectional composites. The measured tensile fracture toughness value is used in a fully validated computational model to simulate the physical test.

Optimization of Taylor spatial frame half-pins diameter for bone deformity correction: Application to femur.

Using external fixtures for bone deformity correction takes advantages of less soft tissue injury, better bone alignment and enhances strain development for bone formation on cutting section, which cause shorter healing time. Among these fixtures, Taylor spatial frame is widely used and includes two rings and six adjustable struts developing 6 degrees of freedom, making them very flexible for this type of application. The current study describes a method to optimize Taylor spatial frame pin-sizes currently chosen from the surgeon's experiences. A three-dimensional model of femur was created from computed tomography images; segmentation of the medical images was made based on the Hounsfield unit (gray scale) in order to allocate adequate mechanical properties into cortical and trabecular bone sections. Both the cortical and trabecular sections were assumed to be isotropic and homogeneous. The diameter optimization of Taylor spatial frame's half-pins was carried out by coupling genetic algorithm and finite element analysis. The finite element analysis was based on a static mechanical load corresponding to a standing person's body weight. Finite element analysis results were validated with experimentally measured strains obtained from bone compression tests. A cost function, based on the developed bone stresses, was defined close to the Taylor spatial frame's half-pins. The calculated cost function showed a decrease of over 33% from the initial half-pin selection by the surgeon and the genetic algorithm optimization. Consequently, the maximum stresses experienced by the bone in the connected location of the half-pins decreased from 121.4 MPa in the surgeon's selection to 73.07 MPa as a result of the optimization process.

Biaxial flexure testing of free-standing thin film membrane with nanoindentation system

The advent of microelectromechanical devices has increased the demand for biaxial flexure testing at the micro- and nanoscale. However, testing at these scales is challenging owing to difficulties in manipulating very small samples and applying highly symmetric biaxial loads to them. In this study, we developed a facile technique for on-chip biaxial flexure testing. The principle of the technique was inspired by ball-on-ring biaxial testing commonly employed for macroscopic flexure analysis of ceramics. In our technique, the specimen is tested as a circular membrane fixed at its edges to a substrate. The center of the membrane is pushed from above by a rounded conical nanoindenter (NI) until the membrane fractures. Since this method does not require microscale specimen manipulation involving the securing of microscale components and/or samples by external fixtures, the test procedure is relatively easy to perform. In addition, the load and displacement curves obtained using the NI are high resolution, enabling precise strength evaluation and application to very weak structures such as nanoscale membranes. To demonstrate the test system, we designed and fabricated polysilicon membranes with diameters of 20 μm and thicknesses of 80 nm. The most likely source of error in the system is misalignment between the indenter and the membrane center. Accordingly, its effect was numerically analyzed. The results showed that a misalignment of less than 3.0 μm causes a 0.32% error in the first principal stress. Since the NI tester can easily attain this alignment accuracy, highly accurate stress estimates can be achieved. The measured fracture strengths of the polysilicon membranes were fitted to the Weibull distribution, revealing an average strength of 8.11 ± 0.31 GPa and a shape parameter of 13.9 ± 5.4, both of which agree well with the results from previous research. The fracture origins were observed near the center of the membranes. These results confirm the viability of our concept.

Boresight Calibration of Mobile Laser Scanner Using an External Fixture

Abstract The boresight misalignment of a mobile laser scanning system is a major source of error for point cloud data and cannot be measured directly. This paper presents a new boresight calibration method for a mobile laser scanner system that uses an external fixture with a simple checkerboard pattern. The boresight angles are determined by minimizing the differences between the measured relative distances of the intersection points of the squares in a checkerboard fixture with the corresponding actual distances in the fixture. Experimental results from scanning the checkerboard pattern on the fixture show that the calibrated values of the boresight angles match the manufacturer’s values within 0.22 cm. Using this simple checkerboard fixture in the field prevents surveyors from having to rely on roadway features or setting control targets and provides for an alternative approach for the boresight calibration of a mobile laser scanner system.

Numerical analysis of the influence of the damping rings’ dimensions on interrupted dynamic tension experiment results

This article discusses the influence of the dimensions of the damping rings used for interrupting a dynamic tension experiment on the results of a modified split Hopkinson tension bar. The damping rings enclosed in an external fixture which modifies the classical split Hopkinson tension bar play a significant role in buffering the dynamic tension experiments before the specimen reaches its failure strength. Finite element simulations of high-strain-rate tension experiments are accomplished on Aluminium 7017-T73 alloy specimens when varying the thickness or the cross-sectional area of the damping rings. Finite element analyses described herein are applied to simulate the effects of the variation of the damping rings’ dimensions to provide a reference for improvement of a modified split Hopkinson tension bar experimental apparatus and guidance for future studies in which optimum dimensions for the damping rings can be studied. In view of this research, it can be concluded that the thickness of the damping rings is a factor that can resolutely influence the interrupted dynamic tension experiment results, while their cross-sectional area can be excluded as a factor influencing the results of the modified split Hopkinson tension bar experiments.

Stretchable, Wireless Sensors and Functional Substrates for Epidermal Characterization of Sweat

This paper introduces materials and architectures for ultrathin, stretchable wireless sensors that mount on functional elastomeric substrates for epidermal analysis of biofluids. Measurement of the volume and chemical properties of sweat via dielectric detection and colorimetry demonstrates some capabilities. Here, inductively coupled sensors consisting of LC resonators with capacitive electrodes show systematic responses to sweat collected in microporous substrates. Interrogation occurs through external coils placed in physical proximity to the devices. The substrates allow spontaneous sweat collection through capillary forces, without the need for complex microfluidic handling systems. Furthermore, colorimetric measurement modes are possible in the same system by introducing indicator compounds into the depths of the substrates, for sensing specific components (OH(-) , H(+) , Cu(+) , and Fe(2+) ) in the sweat. The complete devices offer Young's moduli that are similar to skin, thus allowing highly effective and reliable skin integration without external fixtures. Experimental results demonstrate volumetric measurement of sweat with an accuracy of 0.06 μL/mm(2) with good stability and low drift. Colorimetric responses to pH and concentrations of various ions provide capabilities relevant to analysis of sweat. Similar materials and device designs can be used in monitoring other body fluids.

Internal Joint Restraint Rescues Port of Tampa

This article discusses a project by the Port of Tampa, Florida, to replace a ductile‐iron pipeline that had been eaten through by corrosive, aggressive soil over a period of 35 years. The Tampa Water Department decided on replacing the pipeline with PVC pipe that included an internal joint restraint that eliminated the need for external fixtures. The article discusses installation of the pipe, and explains the internal joint restraint process, which along with the lightweight PVC pipe allowed for quicker installation. The article also discusses PVC product suitability for resisting corrosive soil and holding up to pressure from traffic on an overhead intersection.

Diagnosis

Le Fort II fracture. The 3-dimensional reconstruction computed tomographic scan (Figure 2) showed a Le Fort II fracture, fracture on both sides through the orbital floor (Figure 2, arrow 2), and also through the bridge of the nasal bone (Figure 2, arrow 1). The separated part is triangular or pyramidal in shape, with mobility of the nose. There was also a fracture line on both sides through the maxilla into the nasal cavity, but the nasal septum was intact. A Le Fort I fracture consists of a horizontal fracture of the alveolar process of the maxilla, through the nasal septum. A Le Fort III fracture consists of a horizontal fracture through the orbits with complete separation of the maxilla from the craniofacial skeleton. In comparison to recent pictures of the patient, there was minimal dislocation of the fracture. An external fixture was not placed because of a very poor dental state, and the fracture was treated without any surgery. Images in Emergency MedicineAnnals of Emergency MedicineVol. 45Issue 5PreviewA 61-year-old man was riding his bike when the frame broke and he launched forward and landed on his face. He did not sustain any loss of consciousness. His vital signs were stable and his airway was patent. On physical examination, the patient had several facial lacerations and a nosebleed (Figure 1). The mandible was not dislocated and was nontender on palpation. On further examination, the maxilla could be moved laterally, also demonstrating mobility of the nose. Full-Text PDF

Determining risk factors for methicillin-resistant Staphylococcus aureus carriage after discharge from hospital

At the University Medical Center, Utrecht, methicillin-resistant Staphylococcus aureus (MRSA) patients are considered lifelong MRSA carriers and potentially contagious when readmitted. The purpose of this study was to determine whether patients who become MRSA carriers while in hospital remain colonized after discharge, and whether risk factors for prolonged carriage exist. Thirty-six patients colonized with MRSA during three outbreaks at University Medical Center, Utrecht (group I: 1986–1989), and twenty patients already colonized with MRSA on, or during, admission to the hospital (group II: 1990–1995) were screened for MRSA in two studies. The patients had been discharged from the hospital for periods varying from 15 days to 4·6 years. MRSA was found in five (9%). Four of these patients had skin lesions (wounds), one with an external fixture. The presence of skin- and underlying diseases differed significantly between carriers and non-carriers, supporting the hypothesis that wounds are a major risk factor for long-term MRSA carriage. This study led us to revise our policy concerning readmission of former MRSA patients. We now consider that patients who contracted MRSA in the past no longer need isolation if the following two criteria are met. Absence for at least six months of open wounds, skin lesions, tracheostomy, infections and sources of infection such as abscesses and furuncles, orthopaedic implants, drains, catheters, or tubes. Three MRSA-negative sets of swabs from nose, throat, perineum, urine, and sputum taken at least one hour apart after this six-month period.

A simple apparatus for the measurement of the shear modulus of viscoelastic materials over 4 decades of frequency

Two identical test samples are sandwiched between the metal ends of two small identical piezoelectric stacks, one acting as a transmitter having a displacement proportional to the applied voltage V, the other receiving a charge Q proportional to the force. Since the ends of the stacks are moving out of phase with zero motion at the center, no external fixtures are necessary. The modulus equals Qt(VS)−1(d33)−2, where t and S are the sample's thickness and cross‐sectional area and d33 is a piezoelectric parameter. The useful frequency range is 1–10 000 Hz, which can be extended using smaller parts and different materials for the end plates, and the temperature range is 50–200 °C. The device is limited to low values of dynamic strain.