A Method of Crack Monitoring for Electrically Activated SMA Wires Using Thermography

Predicting the remaining lifetime of an operating shape memory actuator is a great goal to achieve to increase its reliability. The shape memory wires used in these actuators are mostly activated using Joule Heating. Therefore the electrical resistance during activation can easily be measured. Studies show an increase in electrical resistance with an increasing number of activations due to fatigue. Therefore monitoring the electrical resistance leads to a prediction regarding the remaining lifetime of the actuator. The electrical resistance depends on the ambient temperature and the load case (yielded stress, activation frequency, voltage, and current) resulting in different maximum activation temperatures of the wire. The increase in electrical resistance should lead to a higher wire temperature. Before the wire fails due to fracture cumulating cracks should appear. These cracks decrease the diameter of the wire that leads to locally increased electrical resistance and therefore a local higher temperature. This work investigates if those hotspots can be monitored using thermal imaging. Binary Ni50Ti50 wires with a diameter of 0.28 mm were investigated. Measuring the exact temperature of the wires is difficult since the specimens are round and the emission coefficient is unknown. Therefore only qualitative measurement of the temperature is performed. 10 experiments at different stresses and voltages were performed. The results show some indications, that the position and the moment of the fracture can be determined using this setup. Several models are matching the wire temperature after activation to its fracture strength and fatigue behavior. Further investigations must be performed combining the presented models to the results of this work.

Comprehensive Study of the Deformation Behavior during Diffusion Bonding of 1.4301 (AISI 304) as a Function of Material Width and Aspect Ratio

In this paper, the impact of material width as well as aspect ratio on deformation during diffusion bonding of layered samples were investigated. For this, six annular samples with a constant cross-sectional area but an increasing diameter and thus decreasing material width were designed. In a first set of experiments, specimens of a constant height of h = 20 mm were examined. Each sample consisted of 10 sheets, 2 mm in thickness each. Diffusion bonding was performed at T = 1075 °C, t = 4 h and p = 15 MPa. Subsequently, additional samples with a constant aspect ratio of about three but different material width were diffusion bonded. For this, additional layers were added. It was expected that the deformation should be nearly constant for a constant aspect ratio. However, comparing the deformation to a sample possessing an aspect ratio of about three from the first batch, a much higher deformation was obtained now. Bonding a third sample, a deformation in the same range as for the other two samples of the second batch was obtained. It was found that due to the evaporation of metals, the thermocouples were subjected to aging, which was proven indirectly by the evaluation of heating power. Since the diffusion coefficient of the metals follows an exponential law, deformation changes considerably with temperature. This emphasizes that exact temperature measurement is very important, especially for bonding microprocessor devices at constant contact pressure. The experiments showed that the deformation depends strongly on geometry. Bonding parameters cannot be generalized. For layered setups, the contribution that thickness tolerances from manufacturing and leveling of surface roughnesses of sheets add to the overall deformation cannot be reliably separated. After diffusion bonding, thickness tolerances increase with a lateral dimension. Obviously, the stiffness of the pressure dies is crucial.

Co-operative transitions of responsive-polymer coated gold nanoparticles; precision tuning and direct evidence for co-operative aggregation

Responsive polymers and polymer-coated nanoparticles have many potential bio-applications with the crucial parameter being the exact temperature where the transition occurs.

A Differential Quadrature Method for Solving Multi-Dimensional Inverse Heat Conduction Problem

In this paper, the differential quadrature method (DQM) is applied to evaluate the multi-dimensional inverse heat conduction problem (IHCP). The DQM is employed to discretize space domain, and the forward difference method is employed to discretize time domain. Three examples show that the numerical method is accurate. When the noise is added to the exact temperature, the DQM is still a stable and accurate method. Our numerical results are compared with other literatures and show that the method achieves higher accuracy than other methods. Therefore, a simple, convenience, and stable method for evaluate inverse problem is obtained.

The analog linearization of Pt100 working characteristic

The most exact temperature measurement can be made by using platinum sensors. Temperatures from -254.3?C up to +850?C can be measured with Pt100 sensor. The relationship between resistance and temperature is relatively linear, but for measurements of very high precision, Pt100 working curve should be a little bit improved. The paper describes an efficient way of measurement characteristic linearization by using the analogue electric circuits. The obtained results proved the initial considerations and the Pt100 becomes rather transducer than pure sensor.

Experiment Method on the Heat Transfer Coefficient in Air Convection of Young Concrete

Along the process of setting and hardening in concrete, the temperature profile shows gradually a nonlinear distribution due to the development of hydration heat of cement. More specifically, at early ages of concrete structures, this nonlinear distribution has a large influence on the crack evolution. As a result, to obtain the exact temperature history, it is necessary to examine thermal properties of the concrete. In this study, the convective heat transfer coefficient, which presents heat transfer between concrete surface and air ambient, was experimentally investigated with test variables such as velocity of wind, type of form, and water-cement ratio.

Steady State Temperature Gradients in a Non-Blinking Human Eye Prepared for Surgery

LASER surgery on the human eye is intended to reduce a person’s dependency on glasses or contact lenses. Any type of Laser surgery has heat effects on the eye. In laser surgery specific parts of the eye are exposed to concentrated high heat doses, too high heat at a certain spot results in permanent medical damage to the specific exposed eye cells. Precise temperature monitoring of the live interior of the human eye is not possible with the current technology. Published modeling assumes that the human eyeball is at a constant temperature, mostly at 37 °C. Understanding the exact temperature gradients in the prepared open human eyeball in room temperature before surgery is a first step in better understanding the heat effects of either laser surgery on specific treated spots of the cornea, or the effects of insertion of synthetic lenses in the human eye, or treating the retina with laser. In this article the anatomy of the human eyeball, dimensions, and properties are considered in constructing a finite element steady state thermal model of the normal open human eye for an adult, in preparation for surgery under normal room conditions. Also, room boundary conditions are used. Based on the model, the temperature gradients in the open eye are reported.