Strain bridge for load measurement of aircraft folding wing structure will have serious nonlinear response problem in the load calibration ground test. Based on the structural force transmission characteristics and structural load measurement mechanism in the folding region, a piece-wise multivariate linear model is established, with the bending moment with respect to the folding boundary plane being taken as the state variable and the bending moment due to the gravity of the folding section as the boundary load. The method for determining flight measurement load by the piecewise model is presented. The flight test of load measurement of folding wing of a certain type of aircraft is conducted for verification. The results show that the load obtained by the piecewise model is closer to the actual load, and can significantly reduce the influence of the nonlinear response of the strain bridge on load measurement in the folding region and improve the accuracy of the load measurement. At the maximum positive load factor of the symmetric pull-up maneuver, the shear and bending moment obtained by the downward load model are 8.48% and 11.13% smaller than that obtained by the piecewise model, respectively. At the maximum negative load factor of the symmetric push-down maneuver, the shear and bending moment obtained by the upward load model are 14.87% and 12.83% larger than that obtained by the piecewise model, respectively. The research provides a theoretical basis and practical method for solving the nonlinear response problem of strain bridge for load measurement of the wing structure.

In view of the serious influence of temperature on load measurement results of aircraft composite structures, the influence mechanism of temperature on load measurement of aircraft structure was analyzed, and a temperature correction model including the relative response coefficient and thermal output of the strain bridge is established, and the general relation models of relative response coefficient and thermal output with structural temperature are given respectively. These relation models are verified by the temperature test and the temperature-load combined test of composite laminate coupons and the wing box test component. The findings indicate that, when the adhesive's temperature characteristics are met, the relationship between the thermal output and the structural temperature change is a cubic polynomial with zero intercept, and the reciprocal of the relative response coefficient is a power function of the dimensionless structure temperature. By using this technique, the flight measurement results of an aircraft's composite wing structure load can be corrected. The maximum relative change of the pressure center following modification is 30.68%, which greatly increases load measurement accuracy and yields trustworthy data for aircraft flight load verification.