Test Jig Research Articles

Tensile and shear strength measurements on brazed "T" joints used in construction of intra- and intermaxillary hooks.

Silver-brazed "T" joints, representing the first stage in the construction of intermaxillary hooks were fabricated under rigorously controlled conditions. Their tensile and shear strengths were then measured using specially developed test jigs. It was found that the braze joint itself was stronger than the component wires (under tensile load) while in shear mode, fracture occurred in one of a number of well-defined ways. The effect of prolonged heating was investigated using microhardness measurements and recommendations are made for the optimum brazing conditions.

Dynamic restoring and dissipative parameters of non-linear systems

Elastometer vibration and shock absorbing machinery mountings and package cushioning cannot be accurately modeled as linear Voigt type systems, since most of them exhibit stiffening or softening elasticity in conjunction with friction and viscous damping. Improved accuracy may be achieved by a non-linear shock or vibration loaded model, incorporating linear with non-linear elasticity and combined Coulomb and viscous damping. Formulae of such a model are compiled whereby optimal cushioning systems and mounts in shock and vibration loading may be designed. The use of these formulae requires experimental evaluation of two pairs of restoring and dissipative parameters in shock and vibration loading. Equations and test procedures for evaluating these parameters by means of shock and vibration machine tests are presented, along with a detailed discussion of properties of hysteresis loops of non-linear single degree of freedom systems in shock and vibration loading. A special test jig is described comprising a non-linear system with adjustable non-linear elasticity as well as variable Coulomb and viscous damping. This jig was used to evaluate the validity of the mathematical model by means of extensive tests on a shock and vibration machine. Programs developed for an Apple II microcomputer facilitated rapid and accurate computations whereby a numerical example is presented as an illustration of the procedure for evaluating restoring and dissipative parameters. This mathematical model and test procedures are believed to closely approximate shock and vibration isolation systems. As such, they may be conducive to developing better cushioning material and improved machinery mounts.

Wear, Fretting and the Role of Lubricants in Edge Card Connectors

We describe the wear process which occurs when a P.C. card with copper/nickel/solder metallization is inserted into an edge card connector that has a contacting pin with a spherical gold alloy dot and a normal force of about 300 gms. The presence of a lubricant delayed the successive wear processes and reduced the amount of solder displaced during a single pass by minimizing the cold welding of solder to the gold dot. Fretting corrosion experiments were made using a simple test jig which permits the use of actual production cards and connector parts. The fretting test fixture provides a way of comparing and evaluating actual connector designs, as well as a means of comparing the effectiveness of various lubricant formulations.

A fast and accurate method of measuring two-port parameters up to 200 MHz

Design and performance of a test jig is described, which permits the measurement of any set of four complex transistor Y parameters in less than one minute. It is particularly convenient that continuous readings can be taken during bias, frequency, or temperature variations. The vector voltmeter indicates approximate results directly in amplitude and phase. Accurate results must be calculated from the readings.

Test Jig for an Integrating Direct-Reading Spectrograph

Test Jig for an Integrating Direct-Reading Spectrograph

Temperature dependence of the elastic constants of rubidium

Composite tubes are used in numerous applications including aerospace, mechanical, civil and transport sectors, where they may be susceptible to combined loading especially axial compression and torsion and suffer failure due to their intrinsic weakness under such loads. An experimental cum numerical investigation is performed to understand the behaviour of hollow composite tubes with cut-outs under combined axial compression and torsional loadings. Carbon fibre reinforced thermoplastic CF/PEEK tubes with different diameters and varied lay-up sequences, were robotically manufactured using an Automated Fibre Placement (AFP) machine. These specimens were mechanically tested using a novel biaxial test jig, designed specifically to be compatible with an INSTRON 8852 axial/torsion servo hydraulic test system. A standard acrylate coated optical fibre was affixed on the surface of the cylinder for distributed strain sensing using an optical backscatter reflectometer (OBR) interrogator to obtain spatial strain data. Surface strains measured using distributed optical fibre sensing (DOFS) and strain rosettes were compared against finite element analysis predictions to successfully validate the numerical model created using Ansys ACP Pre-Post simulation package. Directional deformations around the cut-outs of these tubes were also numerically characterised and compared with digital image correlation (DIC) results from the experimental tests.

A test jig for measuring transistor current gain in the range 30-300 Mc/s

Common-emitter current gain is measured by comparing the voltages across equal resistors, 10 ω or 75 ω, in the base and collector paths. Coaxially housed tubular high stability carbon resistors are used in a structure which presents a uniform resistance up to 300 Mc/s. The voltages across the resistors are compared by feeding them to a detector via accurately balanced capacitors of about 0.5 pF incorporated in the test jig. Construction and performance of the equipment are described and correction formulae are given relating the measured current gain to the parameter f1. Measurements made on several very high frequency transistors using the test jig and an alternative method employing high grade commercial apparatus showed satisfactory agreement.

Test jig for magnetic cores

Test jig for magnetic cores

A Method of Testing Thin Sheet Material in Compression

A method of determining the compressive mechanical properties of thin sheet material is presented. The test jig, specimen, and details of the testing procedure are described, and the detection of buckling and the measurement of friction between the specimen and the jig are discussed. As a rule, this friction is low enough to be ignored but may be readily determined for each specimen. Results of tests by the pack method, the cylinder method, and the method described, on 0.035-in. thick steel, are given. These indicated good agreement among the three methods. Tests on 0.040-in. thick R301-T aluminum alloy show consistent results from specimen to specimen. Results of tests of 0.020-in. thick clad 24S-T and 0.016-in. thick clad 75S-T aluminum alloys are also given. Test results are presented as stress-strain diagrams. Ease of specimen preparation, simplicity of the jig, and the assurance of low friction between the specimen and its supporting plates are advantages of the test method described.