Abstract: Analyzing a contour of a round bar specimen during uniaxial tensile necking deformation by analyzing a shape of a contour line of a specimen during a necking stage; setting a contour of the specimen at a necking bottom during the necking stage to be S-shaped, and establishing a mathematical model for the contour line; measuring test data of the specimen that has undergone necking deformation, and substituting the measured data into the model to determine shape characteristic values; and substituting the determined values into the model to obtain a curve model of a rotational generatrix of the contour. The method accurately describes the contour rotational generatrix and contour curved surface of the specimen shape during the necking deformation stage in a uniaxial tensile test of a round bar specimen by establishing mathematical models. Advantages include clear physical mechanism, concise mathematical model, and high analytical precision.

Abstract: Analysis method for minimum necking deformation cross-section center stress and strain comprising: recording values for axial acting force, minimum cross-section radius, maximum limit of cross-section radius, inflection point position tangent slope of a rotational generatrix of a contour, radius of cross-section perpendicular to central axis at the inflection point position, and distance between the cross-section perpendicular to the central axis at the inflection point position and minimum cross-section at a necking bottom; and establishing a rectangular coordinate system by taking a center position of the minimum cross-section at the necking bottom as an origin, and substituting the recorded values into mathematical models of a first, second, and third principal stress at a center position of the minimum cross-section to calculate and obtain three principal stress values at the center position of the minimum cross-section, e.g.

Abstract: A system can include a first battery module. The system can include a second battery module. The second battery module can have more lithium iron phosphate (LFP) battery cells than the first battery module.