SI24244A - Apparatus and method for determining and verifying of strength of a mechanically loaded machine part - Google Patents

Abstract

A device for determining and checking the load-carrying capacity of a mechanically loaded machine part, comprising a digital computing unit that is able to calculate voltages and strains in predetermined areas of the mechanically loaded machine part based on the software and the input data according to the end-element method (FEM) in particular on the basis of the geometry data, the mechanical loads to which each machine part is exposed, and the material from which the mechanically loaded machine part consists. In addition to the said digital calculating unit, the device also includes a unit for testing the mechanical properties of the respective material of the respective mechanically loaded machine part of each defining material in which the material is tested in the region of elastic and plastic deformations, and the data is provided to the digital computing unit.

Description

SIEVA, an automotive industry development and marketing company d.o.o.

Apparatus and process for determining and checking the load capacity of a mechanically loaded machine part

The invention relates to a device and a method for determining and checking the load-carrying capacity of a mechanically loaded machine part, in particular a non-standard static and / or dynamically mechanically loaded metal carrier part of a vehicle, machine or other device, which, in addition to elastic deformations, are allowed to be controlled or controlled in addition to elastic deformations. predefined plastic deformations, and at the same time it must be avoided, with high reliability, such deformation or other damage to the mechanical part, that the latter is henceforth unable to withstand the required mechanical loads.

According to the international classification of patents, inventions of this kind are classified in the field of physics, and more specifically in equipment and processes for digital processing of data in connection with a specific purpose, and more specifically in the field of computer aided design.

The invention is based on the problem of making it possible to determine and check the load-carrying capacity of a mechanically loaded machine part of a predetermined geometry, namely shape and dimensions, and consisting of a predetermined material, so that the dimensions of such part would be adequate in comparison with the dimensions of previously known adequate of the parts may be significantly smaller, and as a result, the smaller part would still be able to withstand any mechanical stress to which it is exposed during use.

In addition to functionality, vehicle components must also meet stringent safety requirements. At certain loads, such as vehicle collisions, parts of the vehicle may be deformed plastically but may not collapse, e.g. to breaking or tearing. Plastic deformations in the virtual product testing phase are an indicator that shows how close the critical areas of each part are to the burst. Generally, analyzes based on engineering stress-strain curves are used, which often lead to over-dimensioned construction.

Conventional engineering treatment of the load-carrying capacity of mechanically loaded machine parts is based on the assumption that a mechanically loaded machine part can withstand sovereign and reliable loads, especially in the area below the plasticity limit, in which the part is otherwise elastically deformed, and after relieving the deformations are virtually completely eliminated and the part restores to its starting shape. Depending on the type of loads that may be static or dynamic, e.g. pulse (i.e. pressure only or tensile only) or alternating (i.e. alternately pressure and tensile) the machine part is then dimensioned with an adequate safety margin to allow the work to withstand either constant or occasional static loads or intermittent or permanent dynamic loads.

Such an approach is described, inter alia, in US 2009/0192766, which is to monitor the behavior of two interconnected parts by the finite element method. The essence of this method is to simulate each machine part using a mathematical model that determines the shape of the machine part. The simulated part consists of a finite number of geometrically regular bodies interconnected in corners. Assuming that such a simulated part is subjected to certain mechanical stresses, it is possible to calculate stresses and deformations at individual points, thereby determining the conditions at individual critical points of said part or deformation of the part itself. The deformations depend on the type of material defined by the modulus of elasticity used in the calculation. For verification, it is possible to vary the number and / or size and / or shape of said elements of the mathematical model of the geometry of the work.

Using this engineering approach, the declared load-bearing capacity of a mechanically loaded part depends directly on the modulus of elasticity of the material selected, and on the permissible stress, which is defined as that which the mechanically laden part can withstand loads without deformation from elastic to plastic before the so-called flow limit is exceeded.

This approach results in relatively large-sized machine parts with a correspondingly large mass, which is particularly undesirable in the automotive industry, since heavier mechanical parts of vehicles cause more loads of other components while in use, as well as greater fuel consumption and greater impact on the vehicle. the environment, especially in terms of higher emissions of harmful substances.

A known device for determining and verifying the load-carrying capacity of a mechanically loaded machine part therefore generally comprises a digital computing unit capable of calculating stresses and deformations in predetermined areas of the mechanically loaded machine part based on software and finite element input data (FEM) , especially on the basis of data

- the geometry, namely the shape and dimension of each machine part, which is expressed in the form of a mathematical model consisting of a finite number of geometrically regular bodies, i.e. of finite elements, which are defined by a set of angles, namely points with each time defined spatial coordinates that define the geometry or. rigidity matrix B of volume V, AV;

- the mechanical stresses to which each machine part is exposed and which are expressed e.g. by forces or continuous loads in certain areas of machine work, and / or torques, and

- on a material that is defined at least by means of the modulus of elasticity E and defines the elasticity matrix as a property of the material selected, as well as by the true stress-strain curve, or a flow curve, the calculation in terms of determining or verifying the load carrying capacity of a mechanically loaded part in a digital computing unit, is carried out iteratively by calculating an unbalanced force added for each subsequent step, the following steps being followed in the following order:

i) designing a deformation matrix B based on the geometry of the machine part;

ii) calculation of deformation increment;

iii) calculation of voltage increment;

and wherein the final results obtained each time comprise, on the one hand, information on the loading condition at at least certain points of said machine part and, on the other hand, information on deformations at at least certain points of said machine • a

works resulting from the geometry, mechanical stresses and material selection of said machine part.

The problem posed initially is solved by the apparatus and process in accordance with the characteristics stated in the independent and dependent claims.

According to the invention, there is provided a device for determining and verifying the load-carrying capacity of a mechanically loaded machine part, which in addition to the said digital computing unit also includes a unit for testing the mechanical properties of the material of the respective mechanically loaded machine part of the material.

The said unit for testing mechanical properties is designed in such a way that, on the basis of a standard tube consisting of the said material, it generates data on the functional dependence between the stresses in the material and in the mechanically loaded part from the beginning of its loading through the area of elastic deformation and thereafter also over the entire area of plastic deformation up to the destruction of the material of said tube.

For this purpose, a test tube with a starting length (l ₀ ) and a starting cross-section (A _o ) and consisting of a specific material identical to the material of the mechanically loaded machine part shall be used, with the tube being loaded with a displacement of which the value is incrementally stepped up, while at the same time the load force (F) and the contraction of the cross-section are measured in the range from the initial section (Ao) to the final section (A) or. specific deformations (ε) immediately before the part is bursted.

The action during the stepwise extension of the extension (length or reasonably different dimension) of the test tube can be seen in the enclosed diagrams (Figs. 1 and 2). In general, the relationship between actual and classical engineering calculated stresses and deformations can also be mathematically illustrated, with the actual stress compared to engineering following

where

F represents the force applied to the tube;

σ denotes the voltage in the cross-section of the tube, calculated according to the usual engineering method,

A represents the instantaneous cross-sectional size of the deformed tube;

But _o represents the cross-sectional size of the undeformed tube;

the actual specific deformations ε are as follows compared with the engineering ones calculated

A

Voltage diagrams (Figs. 3 and 4) are also provided to illustrate the output data from Unit 1 for testing mechanical properties and to allow comparison between actual and engineered stress-strain relationships.

Thanks to the presence and use of the said unit for testing the mechanical properties and, in the latter, experimentally obtained data on the actual stresses and deformations in the whole elastic and plastic range, namely the data on the actual strength or. load carrying capacity of a certain material in the whole elastic as well as the plastic region, then the digital computing unit performs the calculation of the stress-strain state in the mechanically loaded part of the known geometry and dimensions, in each case, by the following steps

i) by determining the stiffness matrix of the construction of each mechanically loaded machine part according to formula (I)

K- (I) where

K represents the rigid matrix of the structure;

B represents the deformation matrix (geometry);

E represents the elasticity matrix (material properties)

V, d V represents the volume or. a change thereto;

ii) by calculating the increment of deformations by solving the global system of equations according to formula (II)

KAu = AF Au = K * AF (II) where

F, AF represents the vector of forces or. the increment of forces i.e. load in each step or. in each iteration;

u, and Au represents the displacement vector or. increment of movements in each step or. in each iteration;

iii) by calculating the voltage increment according to formula (III):

Δσ = EBAu (III) where u = u + Διι (IV) and σ = σ + Δσ (V) where σ, Δσ represents the voltage vector or. voltage increment in a single step or. in each iteration;

and then iv) by calculating the plastic deformation increment according to formula (VI)

Δε ^ρ1 = ΒΔιι - E ' ¹ σ (V) where

Δε ^{ρ |} represents the increment of the vector of the plastic fraction of specific deformations ε ^{ρ |} , which is then followed by the calculation of the unbalanced force, which is added to the load before calculating the next step in the said iteration process.

Claims (3)

1. A device for determining and verifying the load-carrying capacity of a mechanically loaded machine part, comprising a digital computing unit capable of calculating stresses and deformations in predetermined areas of the mechanically loaded machine part, based on software and finite element data (FEM) inputs, especially on the basis of data - the geometry, namely the shape and dimension of the respective machine part, expressed in the form of a mathematical model consisting of a finite number of geometrically regular bodies, i.e. of finite elements, which are defined by a set of angles, namely points with each time defined spatial coordinates, which define the geometry or. deformation matrix (B) of volume (V, AV); - the mechanical stresses to which each machine part is exposed and which are expressed e.g. by forces or continuous loads in certain areas of machine work, and / or torques, and - on the material, which is defined by the modulus of elasticity (E) and defines the elasticity matrix as a property of the material selected, as well as by the true stress-strain curve, respectively. a flow curve, the calculation in said digital computing unit being iterated by calculating an unbalanced force, which is added for each subsequent step, and the individual steps are followed in the following order: i) designing a deformation matrix (B) based on the geometry of the machine part; ii) calculating the increment (Δε) of deformation (ε); iii) calculation of voltage increment (Δσ) (σ); and in each case the resulting results include, on the one hand, information on the loading state at at least certain points of said machine part and, on the other hand, information on deformations at at least certain points of said machine part due to the respective geometry, mechanical loads, and the selection of material of said machine part, characterized in that, in addition to said digital computing unit, it also includes a unit for testing the mechanical properties of the material of the respective mechanically loaded machine part of each of the said components, with a digital unit according to the finite element method a cooperating unit for testing the mechanical properties so designed that, on the basis of a standard tube consisting of a material identical to the material of each mechanically loaded machine part, it generates information on the functional dependence between the stresses (σ) in the material and in the mechanically loaded part from the beginning of the loads of extending it over the area of elastic deformation and thereafter over the entire area of plastic deformation up to the destruction of the material of said tube, wherein the unit for testing the mechanical properties of the tube with a starting length (l ₀ ) and a starting cross-section (A _o ) and standing of a material identical to that of a mechanically loaded machine part, adapted to load said tube by a displacement whose value is incrementally incremented, while measuring the respective loading force (F) and the contraction of the cross-section in the area from the initial section (A _o ) to the current cross-section (A) or. Specific deformations (ε) immediately before the fracture of the work, and on the basis of the unit for testing the mechanical properties of the obtained data on the stress-deformation characteristics of the test tube material in the area of elastic and plastic deformations, the digital calculation unit performs the calculation of the stress-strain state in the mechanically selected loads of known geometry and dimensions in each of the following steps i) by determining the stiffness matrix of the construction of each mechanically loaded machine part according to formula (I) K = J * _V Β ^Γ ΕΒί / Γ (I) where K represents the rigid matrix of the structure; B represents the deformation matrix (geometry); E represents the elasticity matrix (material properties) V, dV represents volume ii) by calculating the increment of deformations by solving the global system of equations according to formula (II) KAu = AF - »Au = KAF (II) where F, AF represents the vector of forces or. the increment of forces i.e. load in each step or. in each iteration; u, and Au represents the displacement vector or. increment of movements in each step or. in each iteration; iii) by calculating the voltage increment according to formula (III): Ασ = FBAu (III) where u = u + Au (IV) and σ = σ + Δσ (V) where σ, Δσ represents the voltage vector or. voltage increment in a single step or. in each iteration; and then iv) by calculating the plastic deformation increment according to formula (VI) Δε ^{ρ |} = BAu - E ' ¹ σ (VI) where ε ^ρ1 , Δε ^{ρ |} represents the vector of plastic fraction of specific deformations, respectively. the increment thereof, which is then followed by the calculation of the unbalanced force due to the addition of the load before calculating the next step in the said iteration process. Apparatus according to claim 1, characterized in that the mechanical properties testing unit is adapted to perform a static or dynamic tensile test on the basis of a standardized test tube of the metallic material selected. 3. Procedure for determining and verifying the load-carrying capacity of a mechanically laden machine part by means of a digital computing unit, by means of which, on the basis of software and the finite element method (FEM) data entered, the stresses and deformations are calculated in predetermined areas of the mechanically laden machine part , especially on the basis of data - the geometry, namely the shape and dimension of each machine part, which is expressed in the form of a mathematical model consisting of a finite number of geometrically regular bodies, i.e. of finite elements, which are defined by a set of angles, namely points with each time defined spatial coordinates that define the geometry or. deformation matrix (B) of volume (V, AV); - the mechanical stresses to which each machine part is exposed and which are expressed e.g. by forces or continuous loads in certain areas of machine work, and / or torques, and - on a material that is defined at least by the modulus of elasticity (E) and defines the elasticity matrix as a property of the material selected, as well as by the true stress-strain curve, or the curve of flow, the calculation in said digital computing unit being done iteratively by calculating an unbalanced force, which is added for each subsequent step, and the individual steps are followed in the following order: i) designing a deformation matrix (B) based on the geometry of the machine part; ii) calculating the increment (Δε) of deformation (ε); iii) calculation of the voltage gain (Δσ) (o); in each case, the resulting results include, on the one hand, information on the loading state at at least certain points of said machine part and, on the other hand, information on deformations at at least certain points of said machine part as a result of the geometry, mechanical loads and material selection of said machine part, said digital computing unit being provided with data from the mechanical properties testing unit of the material of the respective mechanically loaded machine part of each of the mechanical calculations, the digital calculating unit being supplied with data from a mechanical testing unit adapted to perform static or • · a dynamic tensile test based on a standardized test tube of metallic material selected, with the unit having a mechanical test tube having a starting length (l ₀ ) and a starting cross-section (A _o ) and consisting of of material that is identical to the material of the mechanically loaded machine part, the data for supplying the digital computing unit is obtained in such a way that the said tube is loaded with a displacement whose value increases steadily, while measuring the respective loading force (F) and contraction of a cross-section in the range from the initial cross-section (A _o ) to the current cross-section (A) or. specific deformation (ε) immediately before the part is bursted, and the information used to supply the digital computing unit for the purpose of calculation is obtained in the mechanical properties testing unit in such a way that, on the basis of a standard tube, consisting of a material consisting of is identical to the material of the mechanically loaded mechanical part of each part, generates data on the functional dependence between the stresses (σ) in the material and in the mechanically stressed part, from the beginning of its loading over the area of elastic deformation and then over the entire area of plastic deformation until the destruction of the material mentioned. tubes. and whereby, based on the mechanical properties testing unit, data on the stress-strain characteristics of the test tube material in the area of elastic and plastic deformation in the digital computing unit, the stress-strain state is calculated in the mechanically loaded part of the geometry and dimensions known at each time, which is done in the following steps i) determining the stiffness matrix of the construction of each mechanically loaded machine part according to formula (I) • · K = J _in Β ^Γ ΕΒί / Γ (I) where K represents the rigid matrix of the structure; B represents the deformation matrix (geometry); E represents the elasticity matrix (material properties); V, dV represents the volume or. a change thereto; ii) calculating the increment of deformations by solving the global system of equations according to formula (II) KAu = AF -> Au = K'AF (II) where F, AF represents the vector of forces or. the increment of forces i.e. load in each step or. in each iteration; u, and Au represents the displacement vector or. increment of movements in each step or. in each iteration; iii) calculating the voltage gain according to formula (III): Δσ = EBAu (III) where u = u + Au (IV) and σ = σ + Δσ (V) where σ, Δσ represents the voltage vector resp. voltage increment in a single step or. in each iteration; • fc then iv) calculation of the plastic deformation increment according to formula (VI) Δε ^ρ1 = BAu - E ' ¹ σ (V) where ε ^{ρ |} , Δε ^ρ1 represents the vector of plastic fraction of specific deformations, respectively. of their increment, which is then followed by the calculation of the unbalanced force, which is added to the load before calculating the next step in the said iteration process.