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A thermocouple is the most widely used electrical component for cost‐effective measurement of temperature in both academia and industry. However, its low sensitivity with typically tens of microvolts per Kelvin needs to be improved to obtain precise measurements. Introduced here is an ionic thermocouple to provide the level of accuracy required of temperature measurements in medicine, precision agriculture, smart buildings, and industrial processes. Ionic conductors are utilized in place of the electrical conductors typically used in the conventional thermocouples (TCs). The ionic thermocouples (i‐TCs) are demonstrated with redox reactions of 10 × 10−3 m potassium ferri/ferrocyanide and 0.7 m iron(II/III) perchlorate, which are electrolytes used as p‐type and an n‐type elements, respectively. The voltage output of the i‐TC that is generated by a change in temperature is approximately two orders of magnitude larger than that of the conventional TC, providing almost two more significant figures in measured temperature. The i‐TC can easily be miniaturized as demonstrated for the in situ temperature measurement of the fluid flowing in the channel of a microfluidic device. A flexible and stretchable i‐TC device is also demonstrated to stably operate up to a tensile strain of 23% with no noticeable degradation in performance.

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Self-piercing riveting (SPR) is a high-speed fastening process that can join similar and dissimilar sheet materials without the need for pre-processing such as drilling or punching. During SPR processes, two overlapping sheets are joined by a rivet. The upper sheet is punched first by the rivet and then the lower sheet is deformed between the rivet and the die, creating a mechanical interlock. In this study, self-piercing riveting of aluminum alloy and carbon fiber reinforced polymer composites (CFRP) sheets was analysed using finite element simulations. For the finite element simulation of SPR processes, the orthogonal elasticity, the fracture model, and the cohesive zone model were used for describing the behaviour of CFRP. For validation of the composite material model, the punching process of CFRP was performed and the results were compared with FE predictions. The SPR process of the aluminum alloy and CFRP was simulated numerically and the performance of the joint was evaluated.