Conductive polymer composites are manufactured by randomly dispersing conductive particles along an insulating polymer matrix. Several authors have attempted to model the piezoresistive response of conductive polymer composites. However, all the proposed models rely upon experimental measurements of the electrical resistance at rest state. Similarly, the models available in literature assume a voltage-independent resistance and a stress-independent area for tunneling conduction. With the aim of developing and validating a more comprehensive model, a test bench capable of exerting controlled forces has been developed. Commercially available sensors—which are manufactured from conductive polymer composites—have been tested at different voltages and stresses, and a model has been derived on the basis of equations for the quantum tunneling conduction through thin insulating film layers. The resistance contribution from the contact resistance has been included in the model together with the resistance contribution from the conductive particles. The proposed model embraces a voltage-dependent behavior for the composite resistance, and a stress-dependent behavior for the tunneling conduction area. The proposed model is capable of predicting sensor current based upon information from the sourcing voltage and the applied stress. This study uses a physical (non-phenomenological) approach for all the phenomena discussed here.

The structural changes of rapidly-quenched amorphous Mg–Cu–Y alloys during time-dependent room-temperature embrittlement were investigated. A continuous reduction in enthalpic content with time, corresponding to a loss in free volume, and radial atomic distances obtained from synchrotron X-ray diffraction experiments imply an overall reduction in volume. Two distinct lifetimes were found by positron annihilation lifetime spectra, with the longer-lifetime component (attributed to areas of larger free volume) vanishing after an ageing time corresponding roughly to the time of embrittlement. Coincidence Doppler broadening suggests that the immediate environment of the annihilation sites is not altered during ageing. The mechanical behaviour correlates with the structural changes in the alloy. The densification observed is assumed to influence the sharp ductile-to-brittle transition in these Mg-based glasses, and the abrupt change in bending ductility is found to result from disappearing large free volume.