A method for assessing the depth of a crack near the surface of a material, characterized in that it comprises the following steps: - heating a zone situated near the crack, using a heat source whereof the heat flow can be modulated periodically according to an adjustable frequency, called modulation frequency, - varying the frequency, so as to vary the thermal diffusion length between an initial value smaller than the distance between the heated zone and the crack and a final value larger than the distance between the heated zone and the crack, the value of the thermal diffusion length being given by the relationship: μ = a. D / f 1 / 2 where: μ designates the thermal diffusion length, a designates a real constant, D designates the thermal diffusivity of the material in m 2 /s, and f designates the frequency of the periodic heat source in Hz, - determining the evolution, based on the thermal diffusion length, of a function based on at least one derivation, with respect to a space variable, of the amplitude of the sinusoidal component of the temperature on the surface of the material and at the modulation frequency, at each of the points of a set of points of the crack, so as to show a first evolution zone of the function in which said function increases according to a first non-zero slope, followed by a second evolution zone in which said function increases according to a second slope different from the first slope, and - evaluating the depth of the crack based on the value of the thermal diffusion length at the intersection of the first evolution zone and the second evolution zone, called intersection length. - heating a zone situated near the crack, using a heat source whereof the heat flow can be modulated periodically according to an adjustable frequency, called modulation frequency, - varying the frequency, so as to vary the thermal diffusion length between an initial value smaller than the distance between the heated zone and the crack and a final value larger than the distance between the heated zone and the crack, the value of the thermal diffusion length being given by the relationship: μ = a. D / f 1 / 2 where: μ designates the thermal diffusion length, a designates a real constant, D designates the thermal diffusivity of the material in m 2 /s, and f designates the frequency of the periodic heat source in Hz, μ designates the thermal diffusion length, a designates a real constant, D designates the thermal diffusivity of the material in m 2 /s, and f designates the frequency of the periodic heat source in Hz, - determining the evolution, based on the thermal diffusion length, of a function based on at least one derivation, with respect to a space variable, of the amplitude of the sinusoidal component of the temperature on the surface of the material and at the modulation frequency, at each of the points of a set of points of the crack, so as to show a first evolution zone of the function in which said function increases according to a first non-zero slope, followed by a second evolution zone in which said function increases according to a second slope different from the first slope, and - evaluating the depth of the crack based on the value of the thermal diffusion length at the intersection of the first evolution zone and the second evolution zone, called intersection length.