A feature of testing complex products is that there are a lot of points for measurements - strain gauges. Multichannel strain gauges and an information-measuring system for strength tests are used for these purposes. This paper explores the method of penalty functions. In those problems where many local solutions are assumed, different versions of existing calculation methods can be used to find the scale minimum of the functional. The expediency of using such options is explained by the fact that the problem being solved is nonlinear. It has been established that if the objective function is continuous, and the allowed area of restrictions forms a closed set, then this will not be enough to determine the optimal parameters when designing machine parts. All parameter values of complex loaded parts, presented as constraints, are divided into sections and intervals. In this case, the interval corresponds to the corresponding segment. When considering a nonlinear system of constraints, the method of penalty functions should be applied. The paper proposes a method for finding the optimal parameters of complex components under load. The study proposes an option for determining the direction of the main axes of the so-called strain tensor, principal strains, and stresses by determining the strains in parts with complex loading.