Reducing Test Runtime by Transforming Test Fixtures

Modal survey testing of the Space Station Common Module Prototype in a test fixture designed to simulate Shuttle Orbiter constraints revealed a number of sources of nonlinearities in the measured frequency response functions. First, the test fixture original design, which utilized spherical bearing joints and an airbag suspension system for offloading the test article weight, is described in detail in order to provide a basis for understanding the test data. Several experimental and analytical lowest-frequency mode shapes are compared, and differences are pointed out. One of the basic modes predicted by the finite element model was not observed at all in the experimental data. Then the measured acceleration/force frequency response functions are examined for different shaker force amplitudes and air pressure levels in the airbag offload system. It is shown that the character of the response functions, and the mode shapes and frequencies of the Common Module, varied depending on the test parameters. Static stiffness and stick-slip measurements for the fixture-to-test-article interfaces were made to provide insight into the behavior of the bearing mechanisms. Careful examination of the experimental mode shapes, frequency responses, static stiffness curves, and bearing stick-slip data led to a determination that the spherical joint interfaces between the Common Module test article and the test fixture were not functioning as designed. Friction in some interface joints prevented relative motion between the test article and fixture that was essential for simulating Shuttle Orbiter constraints of the Common Module in its flight configuration. In other instances, clearances between the spherical bearings and the surfaces of the test article interface structures caused highly nonlinear response as a function of load at the interface. The severity of the unintended joint friction and clearances and the resulting nonlinearities made necessary a redesign of the modal test fixture in the interface regions before the flight constraints of the test article could be adequately simulated.

Estimation of mode II fracture toughness (KIIC) in composite materials is known as a troublous and crucial problem. Dissipated values of KIIC that are reported in different fracture mechanics references is the evidence of the mentioned claim. This problem can signify the necessity of modification on common test methods and fixtures. The present study focuses on the causes of shear test results scattering in composite materials and presents some solutions in the form of necessary corrections that should be performed on the common test fixtures. Mixed mode I/II fracture limit curves are employed to show that the scattering in test results have strong relation with the creation of a considerable Fracture Process Zone (FPZ). It is shown that common test fixtures are blind in confrontation with FPZ and are not able to active toughening mechanisms in pure mode II, correctly. Therefore, estimation of KIIC with available test fixtures has considerable standard deviation. After that, by employing some structural modifications on common fixtures, a new scheme of a shear fixture is proposed that in addition to include the FPZ effects, prepare suitable condition in order to activate the mode II toughening mechanisms. In this regard, it could be found that by applying these reforms, shear load concentration as well as the accuracy of empirical test and repeatability and reproducibility are enhanced. Furthermore, a 3D finite element method (FEM) was considered as the numerical method in which the Iosipesque and new fixture’s specimens were analyzed by ANSYS software. It was found that by applying major amendments in the new shear test fixture, a remarkable precision in results can be obtained in comparison with the previous Iosipesque one

Test fixtures are widely used in industry for quality control to determine the potential of a product to make excessive noise. Since acceptable parts may be rejected unnecessarily, or noisy parts may be passed if the test is inaccurate, it is desirable to have a reliable test setup, including the test fixture. When the part being tested is a motor and gearbox, and the test measurement is vibration, the vibratory response may vary significantly, depending on exactly how the motor and gear tones line up with the test fixture resonances. This potential for variability has led to vibration test fixtures being designed to be as precise as possible, so that the construction of the test fixture can be repeated from one application to the next. However, such an approach has led to rather stiff and massive designs, with few resonant modes, with the result that the repeatability of the measurements can be affected by rather small variations in motor speed and mounting conditions. A similar situation in acoustics leads to the use of reverberation chambers with rotating diffusers. This paper describes an investigation into the possibility of employing a vibration analog to the reverberant room as a test fixture, in order to make vibration measurements on a production line more reliable. The fixture is a plate, sized to achieve a higher modal density than exists in a typical test fixture. The geometry, edge restraints and interior loads are varied, either through analysis or experiments, to produce a variability of response to be averaged over during the data analysis period. Our conclusion is that the reverberant plate test fixture is able to reduce the variability of vibrational response in comparison to a more standard test fixture.

4967147 Circuit tester having mechanical fingers and pogo probes for causing electrical contact with test fixture assemblies

An on-wafer CMOS test fixture employing a grounded polysilicon shield plane is studied in this work. The fabricated polyshielded test fixture is measured and typical parasitic components are extracted. The results are compared to metal-shielded and unshielded test fixture experimental data. In the case of demonstrated fixtures, the polysilicon-based test fixture has 48% lower parallel parasitic signal lead capacitance than a similar metal-shielded test fixture. Moreover, the polysilicon shield does not compromise the isolation between test fixture signal ports. The proposed shielding strategy can reduce the on-wafer measurement uncertainties induced by vertical process tolerances. The test fixtures were fabricated using AMS 4-metal 0.35 /spl mu/m CMOS process.

Chapter 12 - Test fixtures

In microelectromechanical systems (MEMS) ohmic contact switches, reliability is of great concern where billions of cycle operation is a requirement. Microcontact surface tribology plays the critical role in determining their reliability and performance. In this work, a novel, simple, quick and efficient test fixture has been designed and assembled to study the contact resistance, contact force, adhesion force, and contamination associated with the microcontact. In support of developing the test fixture, we evaluated the performance limitations of each components (i.e. piezoelectric actuators, force sensors, nanomax stage) independently. Force versus position, force versus voltage, and position versus voltage data have been collected for each test fixture components under direct current (DC) condition. A customized stage fixture has been 3D printed for holding the microcontact support structure. We use Thorlab’s state-of-the-art nanomax stage to provide nanometric positioning and precise alignment between the microcontact area and the force sensor on three orthogonal axes. We fabricate a novel contact support structure to test the feasibility of our test fixture and collect force and resistance data simultaneously at the rate of $\sim$5 KHz using LabView. Data obtained from the test fixture will provide significant information to design a robust and reliable MEMS switch for future DC and RF applications.

This paper describes a practical test fixture that has been developed for the measurement of shielded screening attenuation (shield effectiveness) of community antenna television (CATV) coaxial cable. The theoretical base of the fixture is contained in the draft Amendment 1 to International Electrotechnical Commission (IEC) Standard 61196-1 and the original German development publications. The test fixture housing is a cylinder that forms a triaxial test configuration with the cable sample shield and centre conductor. The test fixture is thus composed of two regions; the test chamber and the cable sample. The test chamber diameter ratio determines the upper frequency test limit and the lower frequency limit is determined by the length of the cable sample. The sensitivity of the test method is limited by contact resistance where the cable sample shield forms a short circuit with the cylindrical test fixture end plate and by leakage from the cable sample termination which is located within the fixture test chamber. These factors have been minimised to achieve a measurement capability greater than 140 dB over the 1-1000 MHz frequency range. Test results are presented for a selection of braid and combination foil-braid shield designs for RG 6 type coaxial cable measured in lengths up to 6.7 meters over the frequency range 1-1000 MHz. The paper concludes that the test fixture is a satisfactory implementation of the shielded screening attenuation test method. However, recommendations are given for further study of combination foil-braid shield performance.

Saint-Venant End Effects for Anisotropic Materials

The effect of layout design on shield-based test fixture parasitic components is studied in this paper. As a result, guidelines for shield-based test fixture layout design are given. The novel test fixture layout details studied in this paper are a slotted ground plane with different slot orientation, the use of ground-bar extensions in a ground-shielded test fixture, and the upgrade of a ground-shielded test fixture to a fully shielded structure with a common ground. It was found that a slotted ground plane does not increase the ground lead impedance significantly. Thus, successful ground-shielded test fixture processing can be ensured by obeying process stress release design rules. Furthermore, the additional ground bar extensions had a negligible effect on reducing the ground-shielded test fixture ground lead impedance. However, upgrading the ground-shielded test fixture structure to fully shielded reduced the ground lead impedance. Therefore, fully shielded test fixtures are proposed for use with two-port cascade-based deembedding methods, which commonly are incapable of taking into account ground lead parasitic components.

Microelectromechanical systems (MEMS) are an important enabling technology for reducing electronic component geometries and device power consumption. An example of MEMS technology, used in radio frequency (RF) circuits and systems, is the microswitch. Although the operation of microswitches is relatively simple, they are plagued by poor reliability - they must operate over 100 billion cycles. Improvements in the mechanical design of the microswitch have helped to increase their reliability but further improvements are necessary. To accomplish this, research needs to be conducted on the actual contact surfaces for investigation of the mechanical, thermal and electrical phenomena that affect reliability. The focus of this paper is the development of a unique high lifecycle test fixture capable of the simultaneous measurement of contact resistance and contact force. By incorporating a high resonance force sensor, cycle rates reaching 3kHz will be achieved enabling researchers to conduct a wide range of reliability studies. The fixture will be isolated from vibrations and will be housed in a dry-box enclosure to minimize contamination. The test fixture will be automated with control and data acquisition instrumentation to optimize data collection and test repeatability. It is predicted that this new test fixture will provide the potential for significant work to be done to improve the reliability of MEMS microswitches. Several tests were conducted using components of the new test fixture. Preliminary results indicate the feasibility and support the need for the continuing development of this new test fixture.

An improved model for ground-shielded (GS) test fixtures is proposed. The proposed model provides more accurate device-under-test gap behavioral model than previous test-fixture models and takes into account the impedance of the ground return path. The new model is validated up to 25 GHz by comparing the model simulations with experimental measurements. The proposed model is applied to bulk-silicon- and sapphire-based GS test fixtures with different layouts. Furthermore, a large phase shift in the shield-based test-fixture forward transmission is reported in this study. Based on the results achieved, suggestions for deembedding method selection are given. Test fixtures were fabricated using a 0.35-/spl mu/m CMOS process and 0.5-/spl mu/m silicon-on-sapphire CMOS process.

Designing automated tests is a challenging task. One important concern is how to design test fixtures, i.e. code that initializes and configures the system under test so that it is in an appropriate state for running particular automated tests. Test designers may have to choose between writing in-line fixture code for each test or refactor fixture code so that it can be reused for other tests. Deciding on which approach to use is a balancing act, often trading off maintenance overhead with slow test execution. Additionally, over time, test code quality can erode and test smells can develop, such as the occurrence of overly general fixtures, obscure in-line code and dead fields. In this paper, we show that test smells related to fixture set-up occur in industrial projects. We present a static analysis technique to identify fixture related test smells. We implemented this test analysis technique in a tool, called TestHound, which provides reports on test smells and recommendations for refactoring the smelly test code. We evaluate the tool through three industrial case studies and show that developers find that the tool helps them to understand, reflect on and adjust test code.

Shear punch tests performed using a new low compliance test fixture

Vibration testing on telemetry system payload is needed to determine its resistance to vibration during operation. Vibration testing of telemetry system payloads requires a test fixture. Test fixture is used to transmit vibration from shaker to telemetry system payload. The payload of telemetry system to be tested is a tubular. The test fixture in this study was designed using SolidWorks software. The material used for manufacture of test fixture is aluminum. Aluminum material was chosen because it has good rigidity with a relatively light mass. Stiffness and mass properties affect to natural frequency value of test fixture, which must be greater than the frequency range of operating telemetry system. Data collection uses two accelerometers placed on test fixture. Sine sweep vibrations are given from 5 Hz to 2000 Hz with a constant amplitude of 1 g and a sweep rate of 1 octave/minute. The test produces three peaks that they are candidates as natural frequencies, i.e at a frequency of 1532 Hz with an amplitude of 2.898 g, a frequency of 1706 Hz with an amplitude of 6.582 g, and at a frequency of 1806 Hz with an amplitude of 6.472 g. From those three natural frequencies, the second natural frequency at 1706 Hz is the most critically because it has the largest response value.