JPH01167622A - Method for measuring bolt shearing stress - Google Patents

Abstract

PURPOSE:To measure shearing force on an off-line basis at all times with a simple constitution by grinding both ends of a bolt flatly and making the diameter of a bolt hole larger than the deflection margin of the bolt, and measuring the expansion/contraction strain of the ground surface. CONSTITUTION:Both surfaces of the bolt 3 are ground nearby where a shearing force is applied at right angles to the application direction so that both surfaces become parallel and flat. The bolt hole diameter 4 of one of plate materials 1 and 2 is made larger than the bolt diameter and the gap is made larger than the deflection margin of the bolt 3. The bolt 3 is applied with the shearing force and the current expansion or contraction is measured by a strain gauge 6 provided to the ground surface. The shearing force is calculated from the expansion/contraction strain according to a specific relational expression.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for measuring bolt shear stress by measuring expansion and contraction strain.

(Prior Art) For example, when two or more plates 1.2 are connected by bolts 3 as shown in FIG. 1, in most cases, the strength of the bolts is controlled by the shear stress of the bolts. Therefore, it is necessary to measure the shear stress (shear force/cross-sectional area of the bolt) applied to the bolt 3.

If there is only one bolt, attach a strain gauge 6 to area A near the bolt as shown in Figure 1, and multiply the elongation strain measured by this by the longitudinal elastic modulus (Young's modulus) of the plate material. The shear stress of the bolt can be determined.

However, the measurement method is difficult when there are multiple bolts and the shearing force applied to each bolt is not uniform. Such non-uniformity of shear force is likely to occur in reality due to the fit between bolts and bolt holes, variations in the fastening force between bolts and bolts, etc.

Thus, conventionally it has been impossible to directly account for the shear stress of individual bolts. This is because there were no shear strain gauges or strain gauges that could be used while fitting into bolt holes like bolts.

(Problem to be solved by the invention) The reasons for the impossibility of measurement are mainly due to the following two points.

(1) Since the shearing force is applied locally to the bolt (mostly in the cross section), it is too large to be measured by a strain gauge.

(2) In the case shown in Figure 1, the bolt and the plate come into contact, making it difficult to attach a strain gauge to the bolt itself.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for determining shear force from other strains (usually measured with a strain gauge) that can be measured using the formulas for beam bending in mechanics of materials.

(Means for Solving the Problems) The gist of the present invention is that, when measuring the shear stress of a bolt, (+) the part to which shear stress is applied is to be flattened on both sides of the bolt in a direction perpendicular to the shear load. , (ii) By making the bolt hole diameter of the bolt fixed part, which is the part where shear stress is applied, larger than the deflection allowance of the bolt, or by making the bolt diameter smaller, a bending stress is generated in the same part, and ( iii) A method for measuring bolt shear stress by measuring stretching strain, which comprises: determining the shear stress of the bolt by measuring the stretching strain of the shaved surfaces of both sides of the bolt, for example, by pasting a strain gauge on the linear surface. be.

That is, according to the present invention, instead of directly measuring the shear force or shear stress of the bolt, the expansion and contraction strain of the bolt is measured, and the following means are adopted for this purpose.

(1) Cut both sides of the bolt perpendicular to the direction where the shearing force is applied, for example, by a length that allows the strain gauge to be attached. Be careful to make both sides parallel and flat. Process.

(2) Make the bolt hole diameter on one side of the plate thicker than the bolt diameter, and make the gap larger than the bolt deflection. Leave the other bolt holes fixed.

(3) Apply shear stress to the bolt and measure its expansion and contraction using the strain gauge attached to the above-mentioned parallel surface.

The shear stress is calculated from the expansion/contraction strain obtained at this time using a relational expression described in detail later.

(effect) The invention will now be further described in connection with the accompanying drawings.

Figure 2 1M) is a cross-sectional view of the bolt connection under no load, the same) and C1 is the same cross-sectional view under load, but the bolt hole diameter is not enlarged, so the gauge is The case in which strain cannot be measured (FIG. 2 TC) is a desirable case illustrating the measurement method according to the present invention, and the cut-out portion can be approximately considered to be a cantilever bend.

In any of the two cases shown in FIGS. 2(a) to 2(C), strain gauges 6 are pasted on the top and bottom cut surfaces of the bolts 3,
The difference between the strain on the elongation side (positive) and the strain on the contraction side (negative) (m
Find the sum of the paired values). From this, the radius of curvature of the neutral plane of the bolt's cut surface can be determined, and the bending moment and shear force on the same plane can be calculated from the formula of mechanics of materials, and the calculated shear force can be applied to the cut surface of the bolt. Dividing by the cross-sectional area gives the shear stress.

As shown in the perspective view in Fig. 3, the bolts 6 are cut perpendicularly to the shearing load applied to them and parallel to each other, but the upper and lower cut surfaces 7.7 are subjected to strain as shown in Fig. 2(a). Paste gauge 6. A strain gauge gives the average strain over its effective length, but since elongation is a positive strain and contraction is a negative strain, in the cases of Figure 2 (mountain) and Figure 4, the positive and negative strains are offset, which makes it difficult to measure. It's inconvenient. Therefore, it is preferable that the strain gauge be as short as possible, and the cutting length may be correspondingly short.

As shown in Figure 2 (al), the bolt hole diameter on one side of the plate is 4.
As a result, the deformation behavior is shown in the same figure (C
) can be approximated by a cantilever beam. The right fitting part of C1 is fixed, and the lower left point of force is considered to be a concentrated load.If one bolt hole diameter is not enlarged, the expansion and contraction will occur as shown in Figure 2 (see Figure 2) and Figure 4. The offset strain will be displayed, so you won't know where the strain is being measured.

Here, according to what mechanics of materials teaches, 1ii
d”v ρ dx' MF= □ ・ ・ ・(2) There is the following relationship.

However, M = Bending moment (cm-kgf) E: Modulus of longitudinal elasticity (kgf/cd) ■: Moment of inertia of cross section) (c+*') ρ: Radius of curvature (cm) ε: Expansion strain (elongation +, Shrinkage-) V: Deflection (cm) h: Beam height (C-) F: Shearing force (kgf) It is sufficient that the gap due to the enlargement of the bolt hole diameter has a size corresponding to the maximum amount of deflection of the bolt.

This maximum deflection amount can be easily calculated from the teachings of mechanics of materials by considering the bolt as a cantilever beam.

In the bending test, the radius of curvature ρ is determined by equation (3) from the difference in strain between the upper and lower sides, and the bending moment is obtained from ρ using equation (1). On the other hand, by integrating twice, the deflection V can be obtained. The integral constant is the shear force F obtained by differentiating equation (2) from the zero bending moment M obtained from the boundary conditions, and F
Divide by the cross-sectional area to find the shear stress.

Note that the "cross section" mentioned above is the cross section after cutting, and not only the cross sectional area but also the moment of inertia of the cross section is the same.

Therefore, the bolt shear stress to be determined is determined by correcting the above cross-sectional area.

Next, a case will be described in which the above measurement method is applied to a specific example.

(Example) Strain was measured by the method shown in Figures 2) and (e). The bolt diameter is 6. On+m, both sides were ground so that the flat part thickness was 4.5 mm, and strain gauges were attached to both sides. The deflection of the bolt is 0.3
m-, so the bolt hole diameter was set to 6.6 mm. In the case of Figure 2), the bolt hole diameter is 6. It was a sardine.

In addition, in the actual test, it is preferable not to change the bolt hole diameter and to prepare a thinner bolt for the test.

A CEJ load was continuously applied to the bolted connection part constructed in this way, and the changes in the expansion and contraction stress (kgf/mm'') at that time were observed, and the results are shown graphically in FIG.

As can be seen from Figure 5, if only the processing shown in Figure 2) is performed, the output may show an O load even though a C load is applied, which may cause measurement errors. I understand.

By performing processing as shown in Figure 2 (C1), normal measurements were possible.

The expansion and contraction stress obtained at this time was 10.5 kgf/mm”
From this, the shear stress is calculated as 1.54 kg
f/ma+”.

This value is 1.61kgf, which was actually obtained through a destructive test.
When compared with 1-12, it was almost the same.

(Effects of the Invention) Until now, when selecting bolt dimensions, data could only be obtained through calculation or off-line destructive testing, and it was not possible to quantitatively determine compliance. For example, measurements can be performed online at all times by simply preparing test bolts separately, and therefore, the present invention has a remarkable effect as an equipment diagnosis technique.

[Brief explanation of the drawing]

Fig. 1 is a side cross-sectional view of a bolt connection between two plates; Fig. 2 is a side cross-sectional view of two plates connected by a machined bolt; When one bolt hole diameter is enlarged, the same figure (bl shows the deformation when the bolt hole diameter is not enlarged and the load is applied, and the same figure (C1 shows the deformation when the bolt hole diameter is enlarged and the load is applied). Fig. 3 is a schematic perspective view of the bolt after cutting; Fig. 4 is a partial sectional view of the bolt with a strain gauge attached in the case of Fig. 2; It is a graph showing the measurement results of Examples. 1.2: Plate material 3: Bolt 4: Bolt hole diameter 6: Strain gauge

Claims (1)

[Scope of Claims] In measuring the shear stress of a bolt, (i) the part to which the shear stress is applied is ground flat on both sides of the bolt in the direction perpendicular to the shear load; (ii) the part to which the bolt is fixed corresponds to the part to which the shear stress is applied. By making the bolt hole diameter larger than the deflection allowance of the bolt or by making the bolt diameter smaller, bending stress is generated in the same part, and (iii) measuring the expansion and contraction strain of the shaved surfaces on both sides of the bolt. A method for measuring bolt shear stress by stretching strain measurement, comprising: determining the shear stress of the bolt.