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DURING recent years strain gauges have been used more and more in the aircraft industry as a means of assessing the loads in aircraft structures, both in structural testing laboratories and in flight. This increased use can be mainly attributed to the satisfactory development of successful electrical strain gauges of the resistance type and to the demand by engineers for a more complete knowledge of the load distribution in modern aircraft structures. Electrical strain gauges, although requiring accurate apparatus and a large amount of electrical wiring in addition, are much more easily attached to the structure than mechanical gauges and have the great advantage that they can be mounted in positions inaccessible to most mechanical gauges. This increased use of such gauges has been applied to the determination of the loads in tubes under combined bending and direct loading and to obtaining the direct and shear stresses in sheets and panels. The results of all this has been that more engineers have had reason to use the basic formulae for determining these quantities from the measured strains on three or more gauge lines.

The purpose of this paper is to present a measurement technique wherein the film thickness is measured in unfired condition for entire stroke length but without impairing the original condition of piston ring, liner and lubricant, i.e. non-invasively. Film thickness is measured at different speeds up to 500 rpm. The measurements are initially carried out at near zero speed followed by speeds mentioned above. Measurement highlights the combined effect of variation of bore diameter and ring face profile on the film thickness.

The film thickness is measured with the help of a set of strain gauges. Four strain gauges are mounted on a sufficiently elastic steel strip which is mounted in a simply supported condition. This assembly of strain gauge is mounted on small rectangular bracket. A cutout is made in the piston to accommodate the bracket. A pin bearing a slot of size sufficient enough to accommodate the piston ring on one side is fixed between the piston ring and the strain gauge assembly. This ensures the transfer of the movement of the piston ring on to the strain gauge. The deflection of the strain gauge is pre-calibrated against a sufficiently accurate dial gauge. Hence any radial movement of the piston ring is sensed by the strain gauge assembly. A data logger unit is connected to the strain gauge output to log the data at every crank angle. A rotary encoder is connected to the crank shaft, to have the correlation of the strain gauge output with the crank angle.

The technique is capable of measuring oil film thickness for entire stroke at low speeds in unfired engines. The effect of variation in bore diameter on the oil film thickness is significant and hence such measurement can enlighten the path for research to reduce friction. The experimental results of the oil film thickness are in good agreement with predicted values, particularly in the forward stroke (BDC to TDC).

The methodology is not suitable for fired engines as on date but can be taken up as a future work with necessary modifications. It does not take into consideration the effect of elasto-hydrodynamic lubrication.

It can be used to measure OFT between piston ring and liner in unfired engines and reciprocating compressors also.

It can help to indentify the areas of research so that the friction between piston ring and liner can be reduced thus increasing efficiency of the engine and reducing fuel consumption and emissions.

The work presented is a part of PhD work under progress at S V National Institute of Technology, Surat, India. The setup is in the college premises and the experiments are conducted on the same.

STRAIN‐GAUGE technique might, at first glance, seem so highly technical a subject as to occasion some surprise at interest in it at a time when production problems seem to require all of our attention. Actually, of course, the greatest possible aid to increased ease in production is to start with the original design and simplify the structure itself, resulting naturally in a simplification of the entire production problem right from the outset. Better understanding of the problems involved already has allowed considerable progress in the matter of reducing the complexity of aircraft structures. So far, every effort has been made to limit the application of the techniques about to be discussed to those problems for which solutions are needed most urgently, always with the idea in mind of reducing the factors of ignorance involved to the point that we are permitted to simplify the structures which may be in question. The very words “strain gauge” infer a primary concern with theory, due largely to their past limitation to laboratory work. They are, however, here discussed as a work‐a‐day aid to the structural designer, substantiating past decisions and supplying information for better future decisions. In general, these methods, in a halting sort of way, provide a seventh sense that permits the designer to see and understand the inner workings of a structure under load.

This paper presents results of work aimed at characterising the zero offset stability in novel thick film strain gauges. The devices studied are z‐axis (k₃₃) load sensors fabricated on insulated stainless steel substrates and include examples of novel commercially developed force sensors. Devices loaded with compressive strains using a purpose designed test jig were found to exhibit a significant zero offset shift, which is negative up to a certain level (typically 1,000 micro strains) and then increasingly positive when strained beyond this point. Repeated cycles of loading then produced a certain level of stability until the previous maximum value of applied strain was exceeded. Temperature coefficient of resistance (TCR) measurements showed the devices to exhibit characteristics that depend significantly on the device geometry. The TCR was found to increase positively with increasing device thickness and surface area. The effect of overglazing the devices was found to decrease the TCR.

The purpose of this paper is to describe a wireless strain sensor system which will allow easier collection of accurate strain signals in civil engineering structures. The sensor system is developed by integrating with resistance strain gauge, and the data fusion method is proposed based on batch estimation theory.

The principle of resistance strain gauge is discussed and the project of wireless acquisition system of strain signal is given. Wireless strain sensor is integrated with modularization method. Based on batch estimation theory, the data fusion method of strain signal is described. The experiment of wireless strain sensor system is finished on a typical concrete beam structure, the measure data processed by using the data fusion method and the arithmetic average value method is compared and analyzed.

The research result shows that the wireless strain sensor can be installed easily and thus is applied compatibly to local monitoring in civil engineering. The strain signal processed by the data fusion method is more accurate than the one processed by the arithmetic average value method, and thus the proposed data fusion method is fit for processing such slowly‐changing signals as strain.

In this paper, the innovation is shown from two views: one is applying wireless technique to collect strain signals; another is that data fusion with wide application can make measurements more precise and reliable by eliminating uncertain value than using the arithmetic average value method. In general, the developed wireless sensor system and the proposed data fusion method are fit for local monitoring.

THE USE of electrical resistance strain gauges is becoming standard practice in a number of industries, and their introduction into engineering courses is increasing.

The paper gives a review of the present knowledge of the piezoresistive properties of thick‐film resistors (TFRs) and shows how they have been exploited for the implementation of strain‐related physical‐quantities transducers. Two types of device are described in some detail. These achievements were made possible by a proper choice of resistive and conductive pastes and their firing conditions, since only in this case useful piezoresistive properties can be achieved that make TFR strain gauges competitive with metal and semiconductive materials. After examining some correlations between gauge factors, composition and structure of TFRs, new data are presented showing how the strain sensitivities may be changed by varying the peak firing temperature, dwell time and the nature of the chemical elements which diffuse from terminations in the films.

The coefficient of thermal expansion (CTE) and modulus of elasticity (ME) values of mortar and stone from room temperature to cryogenic temperatures provide an experimental basis for the design of liquefied natural gas (LNG) storage tanks.

The CTE and ME of mortar and limestone were measured by resistance strain gauge testing technology at cryogenic temperatures.

The test results showed that CTE values of mortar and stone decreased with the decrease of temperature and CTE values of mortar was greater than that of stone from 0 °C to −165 °C. The ME values of mortar increased significantly at cryogenic temperatures, and less change in stone.

The material at cryogenic temperatures may continue to work in the elastic phase due to the continuous increase of elastic modulus. Therefore, the study of material in the elastic stage may be more important than in the ultimate bearing capacity stage, and it is necessary to carry out further study surrounding the deformation properties of materials at cryogenic temperatures. The CTE and ME values of mortar and stone from room temperature to cryogenic temperatures provide an experimental basis for the design of LNG storage tanks.

The purpose of this paper is the production of mechanical meta-material samples by rapid prototyping (RP) and replica technique for patient-specific skin graft or cranial implant applications in tissue engineering.

Positive moulds (patterns) were produced by stereolithography-based RP. Impression moulding method was used for the production of silicone products (skin grafts). Alginate was used as a moulding material (negative mould). Room temperature vulcanising silicone was poured into the cavity of alginate mould and then products were produced. TiO₂ powder and carbon fibres were used as reinforcement. Meta-material structured polyurethane reinforced silicone composites were also produced. Liquid components (diisocyanate and polyol) were poured into the mould and then polyurethane was produced. Then, polyurethane was immersed in the liquid silicone.

It is found that non-destructive ultrasonic test is a fast and reliable method. Meta-material-based composites show dome-shaped tensile/synclastic surface properties which are important for the skin graft and cranial implants. Increasing the amounts of cross-linking agent and TiO₂ particles increased the hardness and elastic modulus. Carbon fibre addition enhanced the elastic modulus.

Although there are studies on the meta-materials, there is limited study on the RP of the meta-materials for patient-specific implants (skin grafts). Auxetic surface shows perfect fit to curved surface of the skull. Although there are studies on the silicone and polyurethane composites, there is limited study on the characterisation of mechanical properties by ultrasonic tests and strain gauge analysis.

Cantilever. In this experiment a mild steel cantilever beam is arranged so that it cannot be over‐strained. The end travel is limited by contact with the base of the apparatus when fully deflected, see Figure 1.