Strain-gage instrumentation for ammunition testing

This paper deals with a feasibility study on the use of electrical-resistance strain gages for quality-assurance testing of ammunition. A special combination of strain gages was selected to measure the quantity ( \( \in _\theta + v \in _z \) ) on the outer surface of a test barrel. This combination of strain gages was essentially a stress gage which has several advantages over commercially available types. The combined strain signal was proportional to \(\sigma _\theta \) which was related to the internal ballistic pressure. The results of ballistic firings and hydraulic tests are reported which demonstrate the feasibility of this method for acceptance testing of ammunition.     

Strain-gage installations for adverse environments

Seven projects in which resistance-type bonded strain gages were used in adverse environments are described. The projects involved: (1) force measurements in a 10^?10 torr vacuum, (2) load measurements over a temperature range of 75 to 300° F, (3) displacement measurements in a nonconductive fluid at 500° F, (4) dynamic displacement measurements in an electric field, (5) strain measurements in air at 600° F, (6) dynamic displacement and strain measurements to ?320°F, and (7) strain measurements in water at pressures up to 2500 psi and temperatures up to 300° F. This report provides detailed information about the gage installations, the transducers used and the performance obtained.     

Strain-gage Clamping

Experimental Techniques -     

Three Strain-gage Load Measurement

A discussion of the article "Load Measurement in a Cylindrical Column or Beam Using Three Strain Gages" by M.E. Tuttle which appeared in the February 1982 E/T Volume 6, Number 7, 16–17.     

Strain-gage instrumentation for flight-test fatigue measurements

Strain-gage bonding and wiring techniques suitable for use to 600° F are presented. Simple, practical solutions to the problems of temperature compensation are given. Some bridge configurations and circuit requirements for measuring high-temperature fatigue stresses in aircraft are discussed. Techniques for obtaining absolute stresses with strain gages are presented; e.g., production monitoring, reading gages during initial let-down and fueling, and following residual stresses. Mean as well as alternating stress amplitudes are determined. Hence, the true fatigue-load spectrum of an air vehicle can be determined.     

Strain-gage Circuit Calibration Error

Even though significant lead-wire resistances may exist in the constant current potentiometric strain-gage circuit, such resistances need not affect strain response or the measuring circuit. However to avoid errors, lead resistance must be properly accounted for when using the shunt-calibration technique.     

Strain-gage methods for measuring the opening-mode stress-intensity factor,K I

Measurements of strain near a crak tip with electrical-resistance strain gages do not usually provide a reliable measure ofK _I because of local yielding, three-dimensional effects and limited regions for strain-gage placement. This paper develops expressions for the strains in a valid region removed from the crack tip, and indicates procedures for locating and orienting the gages to accurately determineK _I from one or more strain-gage readings.     

Strain-gage technique for measuring internal strains in artificial solids

This paper presents an experimental technique for measuring internal strains of loaded artificial solids by means of single-strand, strain-gage wires. Specifically, in the present investigation, strain-gage wires were embedded lengthwise within rectangular prisms which were made of either pure-epoxy resin or silica crystals in an epoxy-resin matrix. Several prisms of both types were compressed longitudinally or loaded as simply supported beams. Experimentally measured unidirectional internal strains are compared with theoretically expected values, and agreement between experiment and theory is good. Thus, the validity of this new technique is demonstrated.     

Strain-gage stability measurements for three years at 150°C in air

The zero shifts of nickel-chromium foil strain gages (modified Karma) were measured over a period of three years at a constant temperature of 150°C in air. Three gage lengths were included—1.585 mm (1/16 in.), 3.170 mm (1/8 in.), and 6.340 mm (1/4 in.). The strain gages were bonded to constant-stress cantilever beams which were subjected to nomial mechanical strain levels of 0, ±780 μm/m, and ± 1350 μm/m. Each strian gage was connected by threewire leads to a Wheatstone-bridge circuit for the test duration. The data support two general observations: (1) short gage lengths suffer larger zero shifts than longer gage lengths, and (2) gages in compression suffer large zero shifts than gages in tension. On the assumption that the major cause of the zero shifts is a combination of corrosion of the foil and creep of the gage/epoxy/beam system, the author suggests a possible way to correct for the zero shift by experimentally determining the combined corrosion/creep effect and substracting it from the strain-gage readings. Some of the data appear to be consistent with this assumption, but some of the data do not.     

船用惯性系统试验安装标校与变形测量

船用惯性系统试验安装标校和变形测量是提高测量精度,保证试验质量的关键技术,因此在对设备的安装误差和船体变形造成的测量误差进行分析的基础上,重点阐述惯性系统试验零位对准和变形测量的相关理论和工程技术。     

Sensor Installation in Rigid Pavement

This unique approach for installing strain gages in PCC pavement sections in the Ohio SHRP Test Road was very successful. All sensors were installed during construction with no delays to the contractor, and all gages performed well in controlled vehicle tests which followed. After two and one-half years, more than 90% of the gages continue to balance electronically and function properly. Data from these sensors are expected to provide engineers with an in-depth understanding of how PCC pavements respond to traffic loads and environmental factors.     

Modeling of the Installation and Stability of Gel Barriers in Main Fractures

A quasi-one-dimensional nonstationary model for the shutoff of water flow into main fractures using Herschel–Bulkley viscoplastic fluid is presented. The mathematical model, developed in a one-dimensional isothermal approximation with the hydrodynamic parameters (pressure and velocity) averaged over the cross section of the fracture, can be used to determine the optimal technological parameters of the shutoff process and the size of gel barriers to provide their stability on exposure to intense filtration flow after the shutoff of the flow into the fracture. The ranges of flow rates which provide shutoff of a fracture of fixed width for the selected gel are determined. The stability of the installed gel barriers is estimated.     

The Influence of Air Entrainment on the Fluid Pressure Transients in a Pumping Installation

A four-equation, two-fluid model of two-component flow has been developed to study the effects of air entrainment on the pressure transients in a pumping installation. A semi-implicit hydrodynamic numerical scheme is applied. Free and dissolved gases in the fluid and cavitation at the gas saturation pressure are modeled. The mechanism and behaviors of the pressure transients are discussed. Numerical experiments show that the first pressure peak is mainly dominated by two factors: one is the delay in wave reflection from the reservoir; the other is the change of wave speed in the mixture, which directly cause changes in wave speed. The magnitude of the first pressure peak depends on the overlapping of the effects of these two factors. The air volume at the check valve is mainly controlled by the local pressure there and the initial air void fraction. Comparably, the air volume at peak level is dependent on the local pressure and air release with initial air entrainment less than 10^-2, but dependent on the local pressure, air release and initial air void fraction together with initial air entrainment greater than 10^-2.     

Strain Gage and Wiring Installation on Gear Teeth Webs and Shafting for Dynamic Operation in Hot Oil Environment

Experimental Techniques -