def true_fracture_stress(fracture_force, initial_cross_section, reduction_area_fracture):
    """
    Calculation of the true fracture stress (euqation FKM Non-linear (static assessment))

    Parameters
    ----------
    fracture_force : float
        from experimental results
    initial_cross_section : float
        cross section of initial tensile sample.
    reduction_area_fracture : float
         directly measured on the fractures sample.

    Returns
    -------
    true_fracture_stress: float
        calculated true fracture stress of the sample.

    """
    return fracture_force/(initial_cross_section * (1. - reduction_area_fracture))