RU1793320C - Prism-shaped sample for determining mechanical properties of materials - Google Patents

Abstract

The invention relates to a test technique. The aim of the invention is to increase the accuracy of evaluating the strength of the material, simplifying tests and reducing the v-laboriousness of the manufacture of the test subject. rastsa. In a prismatic specimen, on its wide face, a central slit is made of a length of 0.84 + 2s1 perpendicular to the axis of the specimen and two-sided symmetrical notches having a broken line shape, communicating with the central slot and having vertical sections of length b 20h, inclined at an angle F. 19.5 ° to the axis of both the sample and perpendicular to the narrow edges of the sample site. All links of the broken line of incisions are separated from each other by through circular cuts of diameter d (1.5-2) I, where h is the thickness of the test sample in the area of incisions; I-width of incisions of the test sample. 3 ill. shear deformations along inclined incisions. The grips of many testing machines are not able to fully compensate for the relative lateral displacement of the sample heads with inclined notches. This reason, as well as the lack of specific sizes of known samples, especially in their relationship with the strength properties of the materials under study, makes the reliability and accuracy of the test results of these samples not high enough. The closest technical solution chosen as a prototype is a prismatic sample for evaluating the strength of the material. It has a central line.

Description

a different slot perpendicular to the axis of the sample, and flat cuts symmetrically located on opposite broad faces of the sample in the form of broken lines that extend from the corresponding ends of the central slot and reach the sides of the sample. The cuts consist of rectilinear sections separated by through cuts, which are made on

one of the gripping parts parallel to the axis of the specimen and are located between the ends of the respective rectilinear sections of the broken line of notches and the end of the specified gripping part,

A disadvantage of the known sample is as follows. Firstly, in view of its rather complicated design, it has a relatively large complexity in manufacturing. Secondly, the process of testing a sample is also quite time-consuming. Indeed, it is necessary to conduct a tensile test individually for each part of the sample between the longitudinal and the slots. For this, special measures must be taken to ensure that the application of the tensile load to each of these parts is strictly coaxial. The simultaneous loading of all sections of the sample requires the manufacture of special devices for the gripping part with longitudinal slots. In addition, in this case, in the zone of inclined sections of the flat incisions, the stress-strain state is substantially distorted and it will be inhomogeneous along the length of the sections. This is the case for the following reason. The part of the sample between the inclined section of the notch, the longitudinal slits and the end of the sample is schematically represented as a beam with a rigid seal at one end (notch zone) and a hinged support at the other end (at the end of the cut). As the specimen is stretched, the material goes into the plastic deformation stage only in the incision zone. Due to the shear along inclined incisions, the entire beam, as a rigid body, rotates around the hinge support. This type of displacement is equivalent to the displacement of the beam during plastic deformation in a rigid embedment with the combined action of a tensile load and bending moment on the beam.

And finally, the accuracy of evaluating the mechanical properties of the material under study when using a known sample will be insufficient due to the fact that its main dimensions are not indicated, especially in connection with the strength properties of the material.

5

0.

5

0 5. 0 5 0 5 0

5

The purpose of the invention is to reduce the complexity of manufacturing, testing the sample and improving the accuracy of evaluating the mechanical properties of the material.

The goal is achieved. that each broken line of notches contains three sections, each of which is quite definitely oriented with respect to the longitudinal axis of the sample, the dividing through-cuts between the sections are made in the form of round holes, and the dimensions of the sample are selected from the conditions obtained below.

A comparative analysis of the claimed technical solution and the prototype shows that the proposed sample is characterized in that the through dividing slots are made round with a diameter d (1.5-2) 1, and the parameters of the central cut and the sections of the cuts are selected from the ratios given below .

Comparison of the claimed sample not only with the prototype, but also with other technical solutions in this area did not allow them to reveal the features that are distinctive for the claimed sample.

In FIG. 1 is a schematic illustration of a claimed sample; FIG. 2 is a section AA in FIG. 1; in FIG. 3 is a ductility diagram of sheet steel 12 x 13.

The sample contains gripping parts 1 and 2, a central slot 3 and flat cuts 6, 7 and 8, 9, made in the form of broken sheets on the opposite wide edges 4 and 5 of the sample. Between the sections of the broken line of incisions made through circular holes 10-13. The first section, counting from the lateral edge of the sample, is perpendicular to its longitudinal axis (Ф 90 °), the second section is inclined to the axis at an angle Ф 19.5 °, and the third section is parallel to the longitudinal axis of the sample (Ф 0 °).

Due to the geometric and force symmetry of the sample relative to its longitudinal axis at any point in the zone of flat incisions, the equality

- l -ctg / f /, (1)

ЈX |

where уХ1 yi, Јxi are, respectively, the shear and elongation strains in the section along the notch portion inclined to the longitudinal axis of the specimen at an angle / Ф /.

For an isotropic material, the similarity condition for stress and strain deviators has the form

Јxi -Јо Ух1У1

 2 g

X1 U1

(2)

where Ko, (J0 are, respectively, the ball co-axes of the strain and stress tensors; 0x1. fx «yi are respectively more normal and the tangential stress in the section along the inclined section of the notches.

In view of the plastic incompressibility of the material, cb is 0. and oh (Oxi + fy + Oz) / 3.

AT

in our case (7Z 0, but due to the fact that

eji 0 (there is a plane deformation and

d (1,5 ... 2) 1. (9) Stresses on each section of flat cuts according to the corresponding formulas of the well-known work, if, taking into account relation (4), substitute 0.25 ctg Ф instead of ctg Ф

 4ai51p / f /. about -

V3 (1 + 3sinM r Oyi,

  - Ez). normal stress in the direction of the inclined section Oyi Ok1 / 2.

T.

where

 CTX1 4-Oy Oxi

°° s

P

barely substituting the found quantities in (2) we get that

rx1yi / 0xi 0.25с1д / Ф /. (4). Provided that the material of the sample in 3 non-flat incisions is isotropic and in the shoulders adjacent to the area of the notches, it is loaded only elastically, the thickness of the sample in the 3s not cut in each section can be

Not

found by the formula

V7

3 sin2 Ф + 0.75 cos2 Ф

sin2 Ф +0.75 cos2 Ф

ps radiated in accordance with a known technique,

where And is the thickness of the sample outside the incision zone (Fig. 2);

Or, OB are the limits of fluidity ST1 and strength of the sample material, respectively.

The study of function (5) showed / that Mi / the minimum value of h takes revenge at Ф 90 ° and, accordingly, is

h 0.7 NOg / sc.

It is advisable that the thickness of the sample in the zone of flat cuts at all rectilinear sections be constant and equal to the value determined by equality (6). At the same time, in the shoulders of flat incisions in areas perpendicular to the longitudinal axis of the specimen (Ф 90 °), the stress intensity Oy is close to the yield strength of the material, and in other parts of the creep.

 To ensure conditions, the uniformity of the stress-strain was in the zone of flat incisions in accordance with the Saint-Venant principle, the width of the incisions I. / Clay of straight sections b and the diameter of the dividing round holes d must satisfy the conditions

l (3 ... 5) h. (7)

, (8)

Txtyi

Oh cos f

V3 (1)

(YU)

twenty

fifteen

where C7I is the voltage intensity. The remaining components of the stress tensor are equal to zero.

We find the length of the central notch a from the condition of the strength of the jumper between holes 10 and 11.

H (a -2d)

0t

01)

25

where the tensile force P is determined by the formula

P 2tX1y1 bh. (12) After substituting the expression txiyi into (12)

30 from (10) at Ф 0 ° we get Р 2 аи bH / V157

We assume that the greatest value of the force P

. takes place at (7 and s. Then, taking into account

the found magnitude of the force P and the expression (6)

from formula (11) we obtain

35 a 0.84b + 2d. (13) The plasticity diagram of the test material (Fig. 3) is the experimental dependence of the strain EY accumulated at the time of destruction of the intensity of the 4Q deformation on the stress stiffness factor K 3 o / Oii. Taking into account (3) and (10), we find that in the zone of any inclined section of flat incisions

TO

/ 3

V1 + 0.25 ctg f

(14)

For sheet metal materials subjected to sheet metal operations

stamping, the most important part of the diagram; ductility at K 0. For an analytical approximation of the ductility diagram of any second-order curve, it suffices to have three points. It is desirable that the midpoint be approximately midway between the extremes. The two extreme points correspond to K 0 (Ф 0 °) and К - 1.73 (Ф 90 °). Provided that the third point corresponds to uniaxial extension (K 1), the middle section of the broken notch

should be inclined to the longitudinal axis of the sample, as follows from formula (14). at an angle of 19.5 °. As mentioned above, in the zone of the inclined section of the notches yxi yi Јxi ctg / Ф /, Јz -Јxi, and the remaining components of the strain tensor are equal to zero. In this case, the strain rate in the area of the inclined section of the notches is determined by the formulas

Јand U1 + ° 25. (fifteen)

or

, I.Sh; GG + 4T J. (16)

For the proposed sample in the transverse section (Ф 90 °), it is advisable to determine the strain intensity by the formula (15), and in the inclined (Ф 19.5 °) and longitudinal (Ф - 0 °) sections, by the formula (16). Recall that here Јх- | the elongation strain in the direction of the notch width, and yxi yi is the relative shift along the notch. -:

During the tensile test of the proposed sample, simultaneously the load of notches of all three pairs of symmetrical sections is loaded. The destruction of the material occurs sequentially, first in the extreme transverse sections, then on the inclined, and then in the longitudinal sections .-, .-.

Formula and Zobrete.n and Prismatic specimen for evaluating the mechanical properties of a material, having a central slit of length a, made on a wide face of the specimen / perpendicular to its axis, and two-sided symmetrical notch-shaped incisions lines communicating with the central cut and having vertical sections of length L, inclined at an angle Φ to the axis of the sample and perpendicular to the narrow edges of the sample, and all the links of the broken line of notches are separated from each other by through-cuts, distinguishing in order to increasing the accuracy of evaluating the strength of the material, simplifying testing and reducing the complexity of manufacturing the sample, end-to-end separators

Thus, compared with the sample, the claimed sample has a lower laboriousness of manufacturing (round holes instead of dividing through

longitudinal sections to the end of the specimen), testing and high accuracy in assessing the mechanical properties of the material due to the specification of the dimensions of the specimen.

The proposed design of the sample was tested on the example of sheet steel 12 x 13 with a thickness of H 5 mm in the delivery state. Material has characteristics: 0V

450 MPa, stem 650 MPa. According to formulas (6) - (9), (13), the following values of the sample sizes h 2.42 mm (received Г1 2 mm), 1 10 mm, b 40 mm, d 15 mm, and 63.3 mm (taken a 65 mm). In all areas

a notch was applied to a dividing grid with a square cell of 1 x 1 mm. After testing the sample on an instrumental microscope, the parameters of the distorted dividing grid were measured and calculated

according to formulas (15) and (16), the values of the ultimate strain rate for each section of the incisions. The averaged values for each pair of symmetrically spaced sections are as follows: K 1.73 (Ф 90 °),

Ј „0.60; K-1 (Ф 19.5 °), her 0.81: К 0 (Ф 0), Ј and 1.39. The ductility diagram of sheet steel 12x13 is shown in FIG. 3.

The slots are made round with a diameter d (1.5-2) 1, and the parameters of the central slot1 and the notch links are selected from the following conditions:

a 0.84b + 2d;

b 20g., 5 °;

h 0.7H ov / o;

(3-5) h,

where h is the thickness of the test sample in the incision zone;

H is the thickness of the test sample outside the incision zone;

I is the width of the incisions of the test sample;

7g - yield strength of the sample material;

 tensile strength of the sample material.