For several years it has been possible to measure the uniaxial strain dependence of the critical current density JC(ε) of (RE)BCO coated conductors ((RE)BCO tapes) and a parabolic strain dependence of JC(ε) has been observed. To improve our understanding of how strain affects the electrical and mechanical properties of a SuperPower APC SCS4050 (RE)BCO tape, we have created a biaxial sample holder which can apply arbitrary strains along both the xand y-axes of a (RE)BCO tape simultaneously. It can be used to measure JC for independently controllable applied x and y strains ranging from −0.50% ≤ εx ≤ 0.30% and −0.15% ≤ εy ≤ 0.20% respectively, at 77 K. We present the results of JC measurements over this strain range at 77 K in magnetic fields of up to 0.7 T. We show that we obtain the standard parabolic relationship for JC(εx), with a peak in JC occurring at εxP = −0.01%. We also show that when we apply an additional y strain of εy = −0.08% the peak in JC moves to εxP = 0.4%, which cannot be explained by considering the differential strains produced by non-superconducting components of the tape and sample holder. In addition, the value of JC at the peak increases considerably, by 11%.

Recently, we designed and commissioned a 'crossboard' sample holder which can apply biaxial strains in the plane of a (RE)BCO coated conductor. It allows us to measure the critical current density for arbitrary combinations of x-and y-strain. Understanding the in-field, in-plane, biaxial strain dependence of a tape's ( , , ) is crucial for applications such as CORC® or Roebel cables, as the cables are subjected to multiaxial strains during manufacturing and operation. Here we present experimental data for ( , ,) on a SuperPower SCS4050 APC tape in magnetic fields up to 0.7 T, at 77 K. We also outline a theoretical model for the biaxial strain dependence of and use it to parameterise our data and show that the fraction of A-domains and B-domains are roughly equal ( = 0.49 ± 0.03) and that the strain sensitivity of the critical temperature is 1.8 ± 0.1 K% -1 and -1.3 ± 0.1 K% -1 along their a-and b-axes respectively, for all the domains in this (RE)BCO tape. For the first time, we show both parabolic and linear strain dependencies of in a single tape by changing the angle between the applied strain direction and the twin boundaries in the (RE)BCO layer.  Index Terms-Critical current, strain measurement, 2G HTS conductors, cuprates.