Design Of Test Fixture Research Articles

Design of dynamic test specimens and fixtures for large structural components of civil aircraft

In the course of designing and certifying civil aircraft, a significant number of dynamic tests are necessary. If the test specimen is too large in volume or weight, it will place higher demands on the loading capacity of the test equipment. The main focus in the design process of dynamic test specimens is to ensure consistency in the dynamic characteristics compared to the original structure, specifically with regard to natural frequency and mode shapes. Factors such as stiffness, damping, and boundary conditions are taken into consideration. In order to facilitate test implementation and reduce manufacturing costs, a combined approach involving finite element analysis and experimental verification is employed to provide guidance for the design of dynamic test specimens and fixtures for civil aircraft.

УНИВЕРСАЛЬНЫЕ КОАКСИАЛЬНО-ПОЛОСКОВОЕ И ЗОНДОВОЕ КОНТАКТНЫЕ УСТРОЙСТВА И СПОСОБЫ ИХ КАЛИБРОВКИ

The design and calibration method for a coaxial-stripline test fixture that provides connection of microwave circuit analyzer of both coaxial measures and microstrip calibrators, as well as the active components under study, such as transistors, are considered. The test fixture provides high repeatability of connecting coaxial measures, microstrip calibrators, and active components being studied and has a small standing-wave ratio and loss. The test fixture is calibrated with using a minimal set of easily calculated microstrip calibrators with low losses, which, taking into account the high repeatability of their connection, reduces the complexity of its calibration and increases the accuracy of transmitting measurement results from the coaxial line to the microstrip line. The possibility of transmitting measurement results from the coaxial line to the microstrip line extends the scope of the State System for Ensuring the Uniformity of Measurements to the microstrip line. The design of the probe test fixture and a method of its calibration by a specialized microstrip calibrator are also given.

On the implementation of FEA for the design and development of a new biaxial tensile test fixture for uniaxial testing machine: a validation for cruciform test specimens

Sheet metals tend to have an anisotropic behavior due do their manufacturing process; hence, specialized equipment is needed for its mechanical characterization. In this work, the design for a biaxial tensile testing fixture, which can be used along with a universal testing machine for the characterization of sheet metals, is presented. First, a conceptual design of the fixture was generated, considering multiple characteristics observed on the devices existing in the literature; this conceptual design was evaluated using finite element analysis (FEA), and the results were validated with a prototype manufactured through additive manufacturing (AM). Based on the conceptual AM prototype, an iterative detailed design was carried out, in which FEA was used to estimate the performance of the fixture during test and dimensioning the different parts. Lastly, a fully functional prototype of the fixture was manufactured and tested with cruciform specimens fabricated from soft materials. The experimental results showed that the movements and performance of the fixture were adequate for the development of a biaxial tensile test. Thereby, the obtained results provide evidence of the advantages of using computer-aided design, FEA and AM synergistically, for the development of the proposed mechanism.

Structural Dynamics Modification of Vibration-Test Fixture

Abstract Vibration tests are designed and executed for verifying the qualification of aerospace hardware. To accomplish this, a test fixture is required, to transmit mechanical energy from the shaker to the test specimen. This paper presents the experimental testing and finite element model correlation of an available vibration test fixture. The objective was to design an optimized fixture in which the first natural frequency was out of the test frequency range (5–2000 Hz). Many iterations of the test were performed, but the results are presented for only the few that contributed to the optimized design of the vibration test fixture. The final optimized design is presented and discussed.

Mixed-mode fracture characteristics of metal-to-metal adhesively bonded joints: experimental and simulation methods

Fracture behavior of adhesively bonded joints subjected to mixed-mode (i.e. mode I+II) loading conditions is of importance in many industrial applications. This research therefore aims to characterise the failure behaviour of metal-to-metal (i.e. both aluminium adherends) adhesive joints using the mixed mode bending test (MMB), adapted from ASTM D6671/D6671M standard, along with instrumentation using acoustic emission (AE) sensor. Twenty-four adhesively bonded specimens were prepared using two types of adhesive bond materials (acrylic, cyanoacrylate) with two different bonded area 65% and 100%. To understand the effect of mixed-mode loading conditions on the failure behavior, two different mixity ratios were achieved through the design of the MMB test fixture and tested for each bonded joint. The AE results during mechanical testing shows that the time domain signals were spread over the loading phase with distinct features for different mixity ratios. They successfully identified the moment of adhesive fracture during every test. Also, the fracture behavior of the bonded joints was simulated using virtual crack closure technique (VCCT) method using finite element method to understand the loading dynamics in specimen when considering a combination of various design parameters. In addition, an analytical method (e.g. corrected beam theory or CBT) was used to determine strain energy release rates of each specimen. The results show that both the brittle and ductile specimens exhibited higher energy release rates when mode II proportion of loading was increased during the crack initiation phase. The proposed measurement can be useful to assess the overall structural health of bonded systems.

Designing a Test Fixture with DFSS Methodology

This paper addresses the application of Design for Six Sigma (DFSS) methodology to the design of a marine riser joint hydraulic line test fixture. The original test fixture was evaluated using Value Steam Mapping (VSM) and appropriate Lean design tools such as 3D Modeling and Finite Element Analysis (FEA). A new test fixture was developed which resulted in improving the process cycle efficiency for the test from 25% to 50% percent, leading to a 50% reduction in test cost. Handling of the new test fixture is greatly improved as compared to the original fixture.

A method for accounting for test fixture compliance when estimating proximal femur stiffness

Fracture testing of cadaveric femora to obtain strength and stiffness information is an active area of research in developing tools for diagnostic prediction of bone strength. These measurements are often used in the estimation and validation of companion finite element models constructed from the femora CT scan data, therefore, the accuracy of the data is of paramount importance. However, experimental stiffness calculated from force–displacement data has largely been ignored by most researchers due to inherent error in the differential displacement measurement obtained when not accounting for testing apparatus compliance. However, having such information is necessary for validation of computational models. Even in the few cases when fixture compliance was considered the measurements showed large lab-to-lab variation due to lack of standardization in fixture design. We examined the compliance of our in-house designed cadaveric femur test fixture to determine the errors we could expect when calculating stiffness from the collected experimental force–displacement data and determined the stiffness of the test fixture to be more than 10 times the stiffness of the stiffest femur in a sample of 44 femora. When correcting the apparent femur stiffness derived from the original data, we found that the largest stiffness was underestimated by about 10%. The study confirmed that considering test fixture compliance is a necessary step in improving the accuracy of fracture test data for characterizing femur stiffness, and highlighted the need for test fixture design standardization for proximal femur fracture testing.

Design and Development of a Test Fixture and Method for Investigation of Impact During Pre-Stressed Compression

Abstract As composites become more integrated into large structures and vehicles, there is a need to design for laminate failure associated with realistic combined loading scenarios. Because a structural composite is typically brittle, impact damage has been extensively studied and residual strength has been evaluated post impact damage. Few studies have been conducted to determine the effects of pre-stressing a composite during impact. In the case of in-plane compression during impact, it has been found that there is a synergistic effect which causes more damage than occurs with a standard compression-after-impact (CAI) test. When compressive pre-stress greater than 70 MPa was applied to 150 mm × 100 mm × 5.4 mm glass fiber/vinyl ester laminates, an impact initiated shear crack (IISC) developed perpendicular to the applied load leading to failure. To accommodate designers concerned with compressively loaded composite structures that may endure an impact event, a test method has been established to conduct compression during impact (CDI) testing. This paper has reported the design, construction, and implementation of an innovative test fixture that enables investigation of failure mechanisms in the CDI test mode.

含金属芯压电纤维的测试标准与夹具设计

As Metal-core Piezoelectric Ceramic Fibers(MPFs),one types of the new piezoelectric devices,have smaller structrures and sizes,it is difficult to find proper mesurement method and corresponding measuring fixture.Therefore,this paper proposed a precise and easily operated method to measure the MPFs.First,the test model was deduced by using the constitutive equations of a MPF,and the measuring steps for electrical performance of the MPF were established.Then,the effect of test fixture on the measurement results was investigated.Experiments show that it is easy to produce deviation when the clamping positions in the middle of the MPF,which can influence the measurement results.When the clamping position is at the end of the MPF,the relative admittance values of resonance and anti-resonance frequency are smaller,which is hard to be measured either.Furthermore,an improper clamping pressure have a strong effect on the measured value due to the smaller size of MPF.Finally,a measurement method without clamping for the MPF was presented.By the proposed methd,the PZN-PZT MPFs were measured,obtained results give the piezoelectric property values by piezoelectric strain d31 of-97pC/N,electromechanical coupling coefficients k31 of 0.197,and dielectric constant e33T of 1 458.This kind of method is accurate,simple operation,and not damage to MPFs,and can be used as a test standard for MPFs.

Design of a Novel Test Fixture to Measure Rotational Core Losses in Machine Laminations

The need for testing magnetic materials used in electric machine laminations and measurements under a rotating field is of importance in machine design. In order to obtain satisfactory experimental data, the design of the measurement apparatus deserves particular attention. The purpose of this paper is to propose a novel design of a magnetic circuit based on the Halbach array, which generates a uniform flux density inside the test specimen for the measurement of rotational core loss. The proposed design is simulated and prototyped, and experimental tests are performed on two different samples of M19 gauge-24 and M36 gauge-29 silicon steel at three different frequencies (60 Hz, 400 Hz, and 1 kHz). The field-metric method is used in this work to evaluate the rotational core losses.

Evaluation of a Single Cell and Candidate Materials with High Water Content Hydrogen in a Generic Solid Oxide Fuel Cell Stack Test Fixture, Part II: Materials and Interface Characterization

A generic solid oxide fuel cell (SOFC) test fixture was developed to evaluate candidate materials under realistic operating conditions. A commercial 50 mm × 50 mm NiO‐YSZ anode‐supported thin YSZ electrolyte cell with lanthanum strontium manganite (LSM)/YSZ cathode was tested to evaluate the stability of candidate materials. The cell was tested in two stages at 800°C: stage I with low (~3% H2O) humidity and stage II with high (~30% H2O) humidity hydrogen fuel in constant voltage or constant current mode. Part I of the work, published previously, provided information regarding the generic test fixture design, materials, cell performance, and optical post‐mortem analysis. In part II, detailed microstructure and interfacial characterizations are reported regarding the SOFC candidate materials: (Mn,Co)‐spinel conductive coating, alumina coating for sealing area, ferritic stainless steel interconnect, refractory sealing glass, and their interactions with each other. Overall, the (Mn,Co)‐spinel coating was very effective in minimizing Cr migration. No Cr was identified in the cathode after 1720 h at 800°C. Aluminization of metallic interconnects also proved to be chemically compatible with alkaline‐earth silicate sealing glass. The details of interfacial reaction and microstructure development are discussed.

De-embedding errors due to inaccurate test fixture characterization

Making high quality vector network analyzer (VNA) measurement is relatively easy with standard coaxial connectors. However, in RF or high speed interconnect applications, test fixtures are usually required to connect the standard coaxial connectors to the device under test (DUT). The test fixtures need to be characterized first and then de-embedded to reveal the measured S parameters of the DUT. A good test fixture design is critical to the measurement accuracy of DUT. In this paper, the de-embedding error due to in-accurate fixture characterization is analyzed. Examples are given to show that for test fixtures with large insertion loss and return loss, a small error in the fixture characterization can lead to significantly larger error in the deembedded result of the DUT.

Symposium on Static and Dynamic Spinal Implants: Are We Evaluating Them Appropriately?

Abstract Although the standard characterizes intervertebral fusion devices with simple symmetric shapes, modern devices may contain more complex geometries that may require a pocket to fully characterize their strength. Test fixture design has proven to significantly affect the static shear result and failure mode of intervertebral fusion devices with a bullet-nose (rounded) design. An initial test using fixtures without pockets was unsuccessful in determining the shear strength of the fusion device bodies. Revised fixtures with a pocket to force shear loading through the center of the device were designed to create a functional failure. For this study, testing was performed using the ASTM recommended 45° Z axis with a spherically attached actuator pushrod in 37 degrees C phosphate buffered saline. The initial stainless steel fixtures featured mating tooth geometry and no pocket, which forced failures to the device teeth only, resulting in expulsion of the device from the testing fixtures. The revised stainless steel fixtures featured the mating tooth geometry and incorporated a larger anterior/posterior contact surface; thus creating a pocket to constrain the bullet-nose device that prevented the device from expelling. The fusion devices tested with the revised fixture design produced a compression-shear failure of permanent plastic deformation of the body of the device resulted in a 90.2 % increase in the mean yield strength as compared to the fusion devices tested with the initial no-pocket design fixture that produced failures of only the device teeth. The results of this study revealed how the static shear result and failure mode can change significantly with minor changes in fixture design.

A Feasibility Study of Ribbon Architecture for PEM Fuel Cells

The feasibility of an alternative fuel cell architecture, called a ribbon membrane electrode assembly (MEA), is demonstrated for low-temperature polymer electrolyte membrane (PEM) fuel cells used in portable power applications by comparing it to a traditional bipolar “stack” architecture. A ribbon MEA consists of adjacent PEM cells sharing a common gas diffusion layer to allow for lateral electrical current flow and an integral gas-tight, conductive interconnect/seal, where adjacent cells meet to prevent reactant gas leakage. The resulting lateral arrangement of MEAs can be used to supply all MEAs simultaneously instead of individual bipolar plates with flow fields for a stack. A pair of two-cell ribbon MEAs, with and without an interconnect/seal, were designed, prototyped, and sealed by thermal pressing. The MEAs were clamped in a two-piece box fixture to provide reactant gases on the anode and cathode sides, hooked to a fuel cell (FC) test stand and yielded an open circuit voltage (OCV) of 1.43 V with an interconnect/seal and 0.6 V without. A two-cell bipolar stack PEMFC with identical MEA specifications had an OCV of 1.86 V. Polarization curves for the ribbon MEA with interconnect/seal showed the sensitivity of performance to clamping pressure and positioning of the copper current collectors. The ribbon MEA polarization curve was also shifted downward by 0.42 V as compared with that of the traditional stack, and suspected causes (e.g., gas leaking) are attributable to the nonoptimal test fixture design. Hence, the ribbon MEA architecture is shown to be feasible. Future work suggested includes improvements to the test fixture design, development of automated manufacturing capabilities for high volume production, and demonstration of a multicell (>2) ribbon MEA PEMFC design.

Automated In-Vitro Testing of Orthopaedic Implants: A Case Study in Shoulder Joint Replacement

This investigation presents the design and preliminary validation of a single station simulator with biaxial motion and loading designed to mimic the kinematics of the glenohumeral joint during arm abduction in the scapular plane. Although the design of the glenoid holder allows the glenoid component to translate in all three axes, it is primarily loaded axially, which brings it into contact with the oscillating humeral head, but is also loaded superiorly to simulate common subluxation of the humeral head. Simulating arm abduction in the scapular plane simplifies component alignment and removes the need for anterior-posterior loading, thereby creating a stable joint without the need to simulate capsular constraints. In this more physiologically accurate simulator design, the load and motion profiles influence the contact kinematics, but the wear path is ultimately determined by the conformity and constraint designed into the bearing couple. The wear data are determined and correlated with clinically retrieved glenoid components, as well as previously reported in-vitro studies, thus verifying use of the simulator in testing alternative materials and designs. The key design features, as well as the improvements proposed through this study, can be incorporated into the design of test fixtures for any other orthopaedic implant such as the hip, knee, spine, elbow, and finger.

Custom Test Fixture Design and Measurement Correlation of Differential Pairs in a Flip-Chip Organic Buildup Package Using Measurement Based De-embedding

The design of a custom test fixture to measure the 4-port S-Parameters of a flip-chip substrate using 4-port network analyzer and fixture de-embedding is presented. Fixture effects for probes and SMA to microstrip launches are removed using measurement based de-embedding through adapter characterization removal. Residual error of de-embedding is presented along with correlation of the model to measurement.

Selection of tested component to predict dynamic properties of large structures by component modal tests

Large flexible structures cause the full-scale ground tests to be impossible sometimes because they are not strong enough to withstand the force of gravity. The focus of the research into this problem is to confirm the dynamic characteristics of large structures without testing the whole structure. Admire et al. used the mass additive method in a modal test to avoid problems associated with design and development of test fixtures for Space Shuttle payloads [1]. Karpel et al. proposed a method to test components with boundary coordinates loaded with rigid, heavy dummy masses supported by soft springs [2]. Dummy masses generate local displacements near the boundaries to predict the dynamic properties of the whole structure. Misawa and Funamoto [3] proposed a method to predict the dynamic characteristics of large structures with component modal tests. In this method, to simulate the dynamic behavior of structures, reduced mass and stiffness matrices of untested components are replaced with a mass and a spring attached to a tested component. Misawa et al. showed a procedure to select a location with additional mass and stiffness for measuring accurate dynamic characteristics of structures by component modal tests [4]. This method needs no CMS.

Chromium Reactions and Transport in Solid Oxide Fuel Cells

With solid oxide fuel cells operating at 800{degree sign}C or lower, metal alloy bipolar plates (interconnects) offer a number of advantages over ceramic interconnects. However, these alloys rely on the formation of a protective chromium based scale, either chromia or a manganese chromium spinel. As metallic bipolar plates have been explored, and used, over the last decade, a number of interactions have been observed between the bipolar plate and various cathode materials. This paper examines the interactions between E-Brite® and an LSM/YSZ composite active cathode. Tests examined direct contact of the E-Brite® with the cathode, and the effect of using gold foil as a physical barrier so only gas phase interactions were possible. Additionally, key observations on test fixture design and materials selection are discussed, which may shed light on why different researchers have observed a wide range of fuel cell degradation rates.

An Experimental Approach for Structural Dynamic Modification of Fixture in Vibration Test Control.

In environmental vibration test, the fixture is inserted between the shaker and the test specimen. It is desirable that the test specimen is excited with uniform force through the mounting points connected to the fixture. The flexural vibration of the fixture sometimes makes it impossible to excite the specimen uniformly. The deviations of the transmitted force cause the under-test, especially at anti-resonance frequencies, in vibration test control. In this paper, the method of experimental structural dynamic modification using transfer function synthesis method is applied to the design of vibration test fixture. The responses at any points on the fixture can be predicted utilizing the experimental data. Structural dynamic modification of fixture is performed so that the spectra at the mounting points may meet the specified reference spectrum. The values of the added masses, which will be attached on the fixture, are used as design variables for removing the under-tests in environmental vibration test. From the experimental results of vibration test control applied to the modified fixture and unmodified fixture, this method is shown to be an effective one.

Flux-canceling electrodynamic maglev suspension: Part I. Test fixture design and modeling

The design and analysis of a scale-model suspension test facility for magnetic levitation (maglev) is discussed. We describe techniques for the design, construction, and testing of a prototype electrodynamic suspension (EDS) levitation system. The viability of future high-temperature superconducting magnet designs for maglev has been investigated with regard to their application to active secondary suspensions. In order to test the viability of a new flux-canceling EDS suspension, a 1/5-scale suspension magnet and guideway was constructed. The suspension was tested by using a high-speed rotating test wheel facility with linear peripheral speed of up to 84 m/s (300 km/h). A set of approximate design tools and scaling laws has been developed in order to evaluate forces and critical velocities in the suspension.