The present disclosure claims priority to patent application No. 202211212028.2, filed to the China National Intellectual Property Administration on Sep. 30, 2022 and entitled “Method for Measuring Residual Stress in Thin Plate”.
The disclosure relates to the technical field of measuring of residual stress in thin plates, and particularly to a method for measuring residual stress in a thin plate.
High-performance thin plates are extensively applied to the fields of aerospace, electrical and electronic engineering, chip package, etc., for example, aircraft skin, chip lead frame processing, transformers and so on. In processes of processing and manufacturing the aircraft skin and chip lead frames by the thin plates, a removed surface area accounts for 80% of a total area, and a removed thickness accounts for 60% or above of a total thickness. The thin plates have low bending stiffness on account of thinness, and will largely deform even under low residual stress during a removal process. The premise of deformation control of the thin plate during the removal process is quantitative characterization of residual stress distribution of the thin plate in a thickness.
In a related art, internal residual stress of the thin plate is generally evaluated through a single-side corrosion method. In this method, one side of the thin plate is required to be protected by pasting a film, the other side of the thin plate is required to be corroded by a corrosive liquid, and after a corrosion depth reaches 50% of the thickness of the thin plate, a warpage deformation quantity is compared. This method can only qualitatively determine magnitude of the residual stress according to a deformation degree, but cannot quantitatively characterize a distribution rule of the residual stress in the thickness of thin plate.
Since the thin plate is not uniformly cooled during solution quenching, residual stress on a surface and at a center of the thin plate have different tensile and compressive states. Therefore, it is difficult to quickly guide optimization of thin plate manufacturing technique according to a deformation law obtained through the single-side corrosion method. With mass supply requirements of civil airliners and high-performance chip packaging materials, a breakthrough on quantitative characterization technique for residual stress of a thin plate is urgently required. Therefore, a method capable of rapidly and quantitatively characterizing residual stress distribution in a thin plate is required to effectively control processing deformation of the thin plate.
Some embodiments of the disclosure provide a method for measuring residual stress in a thin plate, which is used for quantitatively characterizing a distribution rule of the residual stress on a thickness of the thin plate.
In order to realize the above objective, some embodiments of the disclosure provide a method for measuring residual stress in a thin plate. The method includes: S1: prearranging and cutting a plurality of fins that are parallel to a length direction of the thin plate at equal intervals along a width direction of the thin plate, where a length of each fin is the same as each other and less than a width of the thin plate, and the fins have fixed ends and movable ends that are opposite each other, computing x-direction strain εi0 and x-direction residual stress σi0 in the length direction of the thin plate borne by each fin according to lengths of each fin before and after cutting, and obtaining distribution of x-direction residual stress in the width direction of the thin plate according to σi0 of all the fins; S2: repeatedly cutting the fixed end of the each fin in a thickness direction of the thin plate, recording a cutting parameter, and a warpage condition and a bending parameter of the each fin after each cutting, computing a total cutting depth Zij and x-direction residual stress σij of the each fin after each cutting, and obtaining distribution of x-direction residual stress in the thickness direction of the thin plate borne by an ith fin according to all σij; and S3: computing distribution σx, σx=σi0+σij, of x-direction residual stress on a yz cross section of the thin plate according to σi0 of the ith fin computed in S1 and corresponding σij of the ith fin after jth cutting in S2.
In some embodiments, S1 includes: S1.1: arranging cutting marks at equal intervals in the width direction of the thin plate, where an extension direction of each cutting mark is the same as each other and parallel to the length direction of the thin plate and extends to an end of the thin plate, an extension length of each cutting mark is less than a length of the thin plate, and a region between any two cutting marks forms one fin, and recording an initial length L0 of the ith fin before cutting; and S1.2: cutting the cutting marks through the thin plate in the thickness direction of the thin plate, and recording a deformation length Li0 of the each fin after deformation in the length direction of the thin plate.
In some embodiments, S1 further includes: S1.3: computing the x-direction strain εi0 and the x-direction residual stress σi0, εi0=(L0−Li0)/L0 and σi0=Eεi0, in the length direction of the thin plate borne by each fin according to the recorded initial length L0 of the fin and the deformation length Li0 of the fin, where E is an elastic modulus of the thin plate.
In some embodiments, S2 includes: constraining two ends of the thin plate in the length direction before each cutting, so as to make an extension direction of each fin parallel to the width direction of the thin plate, and releasing the thin plate on one side of the movable end of the fin after each cutting, so as to compute and record the bending parameter of the ith fin after jth cutting.
In some embodiments, the total cutting depth Zij and the x-direction residual stress σij of each fin after each cutting are expressed as:
where Δz is a cutting depth of each cutting, t is a cutting width, Iij is inertia moment of an uncut portion of the ith fin after jth cutting, E is a Young's elastic modulus of the thin plate, hij′ is a warpage quantity of the ith fin after jth cutting minus a warpage quantity of a cut portion, hij is a bending height of the ith fin after jth cutting, Lij is a remaining length of the ith fin after jth cutting, S is a thickness of the thin plate, m is an equivalent arc length of residual stress release of the ith fin after jth cutting, and under the condition that t is infinitely close to 0, a computational formula for σij is expressed as:
In some embodiments, m is approximately expressed as: m=t+0.75S; after jth cutting of the ith fin, a notch is formed, and the ith fin is bent to form a first bent surface and a second bent surface that are spaced apart from each other in the thickness direction of the thin plate; on an xz cross section of the thin plate, the first bent surface and the second bent surface are two arcs that have the same curvature but different arc lengths, the equivalent arc length m is a length of an arc formed between two ends of an opening of the notch on the cross section, and curvature of the equivalent arc length m is the same as curvature of the two arcs; and hij′ is a height between a warping end of the opening of the notch on the cross section and a top end of the fin after warping, and hij is a height between a non-warping end of the opening of the notch on the cross section and the top end of the fin after warping.
In some embodiments, σij is obtained according to formulas as follows
where ΣMij is total bending moment of the ith fin after jth cutting, and d(ΣMij) is a bending moment increment of the ith fin after jth cutting.
In some embodiments, a computational method for ΣMij is as follows: ΣMij=ωijMij; where ωij is an average arc length, and Mij is average bending moment of the residual stress of the ith fin after jth cutting on an arc length of any unit; and after jth cutting, the i-th fin is bent to form a first bent surface and a second bent surface that are spaced apart from each other in the thickness direction of the thin plate, on an xz cross section of the thin plate, the first bent surface and the second bent surface are two arcs that have the same curvature but different arc lengths, the average arc length is between the two arcs, curvature of the average arc length is the same as curvature of the two arcs, and distances between the average arc length and the arcs on two sides are the same.
In some embodiments, a computational method for Mij is as follows:
In some embodiments, computational methods for ωij, θij and Iij are as follows:
where ρij is a curvature radius of the ith fin after jth cutting, and θij is a bending angle of the ith fin after jth cutting.
In some embodiments, S2 further includes: correcting the residual stress;
where Δ(σij) is an effect of residual stress of layer Δz on residual stress of the uncut portion, and σij′ is a residual stress correction value of the ith fin during jth cutting.
A technical solution of the disclosure provides a method for measuring residual stress in a thin plate. The method includes: S1: prearranging and cutting a plurality of fins that are parallel to a length direction of the thin plate at equal intervals in a width direction of the thin plate, where a length of each fin is the same as each other and less than a width of the thin plate, and the fins have fixed ends and movable ends that are opposite each other, computing x-direction strain εi0 and x-direction residual stress σi0 in the length direction of the thin plate borne by each fin according to lengths of each fin before and after cutting, and obtaining distribution of x-direction residual stress in the width direction of the thin plate according to σi0 of all the fins; S2: repeatedly cutting the fixed ends of the fins in a thickness direction of the thin plate, recording a cutting parameter, and a warpage condition and a bending parameter of each fin after each cutting, computing a total cutting depth Zij and x-direction residual stress σij of each fin after each cutting, and obtaining distribution of x-direction residual stress in the thickness direction of the thin plate borne by an ith fin according to all σij; and S3: computing distribution σx, σx=σi0+σij, of x-direction residual stress on a yz cross section of the thin plate according to σi0 of the ith fin computed in S1 and corresponding σij of the ith fin after jth cutting in S2. According to this solution, according to distribution of a plurality of x-direction residual stress in the width direction (y direction) and the thickness direction (z direction) of the thin plate, distribution of the residual stress in the thin plate on the yz cross section is obtained, and the situation that a method for evaluating residual stress in a thin plate through a single-side corrosion method in the prior art can only qualitatively determine the residual stress, but cannot quantitatively characterize distribution of the residual stress in a thickness of the thin plate is avoided. Through computation of the solution, the residual stress and the distribution thereof in the thin plate are obtained, and characterization is accurate and reliable.
The accompanying drawings of the description constitute part of the disclosure and serve to provide further understanding of the disclosure, and illustrative examples of the disclosure and the description of the illustrative examples serve to explain the disclosure and are not to be construed as unduly limiting the disclosure. In the accompanying drawings:
The above figures include reference numerals as follows:
Technical solutions in examples of the disclosure will be clearly and completely described below in combination with accompanying drawings in the examples of the disclosure. Apparently, the examples described are merely some examples rather than all examples of the disclosure. The following description of at least one illustrative example is merely illustrative in nature and in no way serves as any limitation of the disclosure and its application or use. On the basis of examples of the disclosure, all other examples obtained by those of ordinary skill in the art without making creative efforts all fall within the scope of protection of the disclosure.
As shown in
In the embodiment, according to distribution of the plurality of x-direction residual stress in the width direction (y direction) and the thickness direction (z direction) of the thin plate, distribution of the residual stress in the thin plate on the yz cross section is obtained, and the situation that a method for evaluating residual stress in a thin plate through a single-side corrosion method in the prior art can only qualitatively determine magnitude of the residual stress, but cannot quantitatively characterize distribution of the residual stress in a thickness of the thin plate is avoided. Through computation of the solution, the residual stress magnitude and the distribution thereof in the thin plate are obtained, and characterization is accurate and reliable.
As shown in
Specifically, as shown in
In some embodiments, S1 further includes: S1.3: compute the x-direction strain εi0 and the x-direction residual stress σi0, εi0=(L0−Li0)/L0 and σi0−Eεi0, in the length direction of the thin plate borne by the each fin according to the recorded initial length L0 of the fin and the deformation length Li0 of the fin, where E is an elastic modulus of the thin plate. As shown in
As shown in
As shown in
where Δz is a cutting depth of each cutting, t is a cutting width, Iij is an inertia moment of an uncut portion of the ith fin after jth cutting, E is a Young's elastic modulus of the thin plate, hij′ is a warpage quantity of the ith fin after jth cutting minus a warpage quantity of a cut portion, hij is a bending height of the ith fin after jth cutting, Lij is a remaining length of the ith fin after jth cutting, S is a thickness of the thin plate, m is an equivalent arc length of residual stress release of the ith fin after jth cutting, and under the condition that t is infinitely close to 0, a computational formula for σij is expressed as
In the embodiment, cutting is carried out through an electric spark electrode discharge cutting method, a cutting direction is perpendicular to a surface of the thin plate, and ends of the fixed ends of all fins are simultaneously cut. In the cases of Lij and the number of times of cutting j=0, Lij=Li0. Since a cutting width t of any fin does not change, a plurality of Lij of an ith fin are the same as each other. For example, L11 of a first fin (fin 1) after first cutting is the same as L12 of the first fin (fin 1) after second cutting. In the cases of hij and j=0, hi0=hij. Since a total cutting depth Zij of any fin progressively increases, a plurality of hij of the ith fin are different from each other. For example, h11 of the first fin (fin 1) after first cutting is different from h12 of the first fin (fin 1) after second cutting, and hij′ is similar.
With fin 1 after two-time cutting as an example, a total cutting depth after second cutting is Z12=2Δz, and residual stress of fin 1 after second cutting is
Therefore, the residual stress of each fin after each cutting may be computed, and distribution of x-direction residual stress in the thickness direction of the thin plate borne by each fin may be obtained according to all the obtained σij. Under the condition that t is infinitely close to 0, residual stress release is small, a bending degree is low, #h
Specifically, j in the embodiment is an integer greater than 0.
In some embodiments, m is approximately expressed as: m=t+0.75S; alter jth cutting of the ith fin, a notch 11 is formed, and the ith fin is bent to form a first bent surface 12 and a second bent surface 13 that are spaced apart from each other in the thickness direction of the thin plate; on an xz cross section of the thin plate, the first bent surface 12 and the second bent surface 13 are two arcs that have the same curvature but different arc lengths, the equivalent arc length m is a length of an arc formed between two ends of an opening of the notch 11 on the cross section, and curvature of the equivalent arc length m is the same as curvature of the two arcs; and hij′ is a height between a warping end of the opening of the notch 11 on the cross section and a top end of the fin ater warping, and hij is a height between a non-warping end of the opening of the notch 11 on the cross section and the top end of the fin after warping.
In the embodiment, hij may be also obtained by a laser displacement sensor. Specifically, coordinates of positions P1′, P2′, P3′ . . . , Pi′ in
In the embodiment, the σij is obtained according to formulas as follows:
where ΣMij is a total bending moment of the ith fin after jth cutting, and d(ΣMij) is a bending moment increment of the ith fin after jth cutting. d(ΣMij)=ΣMij−ΣMi(j-1).
Specifically, a computational method for ΣMij is as follows: ΣMij=ωijMij; wherein ωij
Wherein, a computational method for Mij is as follows
With fin 1 after two-time cutting as an example M12
According to ΣMij=ωijMij, it can be inferred that
With fin 1 after two-time cutting as an example, ΣMij is as follows:
Further, a computational method for ωij is as follows:
wherein ρij is a curvature radius of the ith fin after jth cutting, and θij is a bending angle of the ith fin after jth cutting.
In the embodiment, with fin 1 after two-time cutting as an example,
Alternatively, ρij may be also obtained by a laser displacement sensor, and a measurement method is the same as that for hij.
A computational method for θij is as follows:
With fin 1 after two-time cutting as an example,
Further, a computational method for Iij is as follows:
wherein ρij is a curvature radius of the ith fin after jth cutting, and Mij is a bending moment of the ith fin after jth cutting. With fin 1 after two-time cutting as an example,
In the embodiment, S2 further includes: correct the residual stress;
wherein Δ(σij) is an effect of residual stress of layer Δz on residual stress of the uncut portion, and σij′ is a residual stress correction value of the ith fin during jth cutting. Through such arrangement, distribution reliability of residual stress σij on the thin plate and characterization accuracy are ensured.
What are described above are merely some embodiments of the disclosure and are not intended to limit the disclosure, and for those skilled in the art, the disclosure can be variously modified and changed. Any modification, equivalent substitution, improvement, etc. within the spirit and principles of the disclosure shall fall within the scope of protection of the disclosure.
Number | Date | Country | Kind |
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202211212028.2 | Sep 2022 | CN | national |
Filing Document | Filing Date | Country | Kind |
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PCT/CN2023/105773 | 7/4/2023 | WO |