1 Introduction
2 The ideal weld
3 General assumptions
-
Weld nugget shapes, i.e. circular, square and rectangular,
-
Weld areas,
-
Double systems of welds (serial, parallel) in relation to the direction of shear force.
-
Sheet (specimen) width of 30 mm—in relation to a single joint (one weld) and 55 mm in relation to double joints in the parallel system of welds in relation to the direction of the shear force effect,
-
Sheet length of 70 mm—in relation to a single joint (one weld) and 95 mm in relation to double joints in the serial system in relation to the direction of the shear force effect.
Initial force | Time of current flow | Final force | ||
---|---|---|---|---|
Calculation step | 1 | 1 | 1 | ms |
Recording of data | 5 | 5 | 5 | Steps |
Welding paramaters | ||||
Variant number | Current | Time | Force | Final force |
kA | ms | kN | ms | |
M1–M9 | 0.1 | 1 | 0.1 | – |
M10 (high parameters) | 10 | 160 | 3.0 | 500 |
M11 (low parameters) | 7 | 400 | 1.5 | 500 |
Convergence of calculations (covergence control) | ||||
Degree of convergence | ||||
Electric model | 1.00E−5 | |||
Thermal model | 1.00E−5 | |||
Mechanical model | 1.00E−5 | |||
Heat losses to the environment | ||||
Ambient (air) temperature | 20 | °C | ||
Heat transfer coefficient | 300 | [W/m2*K] | ||
Electrode type | F0 | |||
Welding current type | DC 1 kHz | |||
Force system | Pneumatic |
4 Assumptions for comparative analysis
No. | Variant number | Weld nugget shape | Weld nugget dimensions | Cross-sectional area of joint (weld) | Height of connector | Remarks |
---|---|---|---|---|---|---|
mm | mm2 | mm | ||||
1 | M1 | Circle | ϕ = 6.00 | 28.26 | 0.2 | Reference variant |
2 | M2 | Square | x = y = 5.316 | 28.26 | 0.0 | “Gluing” of sheets |
3 | M3 | Square | x = y = 5.316 | 28.26 | 0.2 | – |
4 | M4 | Rectangle | x = 10.00; y = 2.826 | 28.26 | 0.2 | – |
5 | M5 | Rectangle | x = 2.826; y = 10.00 | 28.26 | 0.2 | – |
6 | M6 | 2 circular weld nuggets | 2 × ϕ = 6.00 | 2 × 28.26 | 0.2 | 2 circular weld nuggets, system of 2 serial welds, l = 50 mm |
7 | M7 | 2 circular weld nuggets | 2 × ϕ = 6.00 | 2 × 28.26 | 0.2 | 2 circular weld nuggets, system of 2 parallel welds, l = 50 mm |
8 | M8 | 2 circular weld nuggets | 2 × ϕ = 4.24 | 2 × 14.13 Σ = 28.26 | 0.2 | 2 circular weld nuggets, system of 2 parallel welds, l = 25 mm |
9 | M9 | Uniform sheet | k = 18.84 mm g = 1.5 mm (Fig. 8) | 28.26 | 0.0 | Non-overlap joint (butt), |
10 | M10 | Circle | ϕ = 6.00 | 28.26 | 0.2 | High welding parameters [H], |
11 | M11 | Circle | ϕ = 6.00 | 28.26 | 0.2 |
5 Description of numerical models
-
Circular weld nugget having nominal diameter ϕ1 = 6.0 mm (S1 = 28.26 mm2) in relation to 1.5-mm-thick sheets (Fig. 2b),
-
Circular weld nugget having half the area S2 = 14.13 mm2 (1/2 × 28.26 mm2), i.e. diameter ϕ2 = 4.24 mm,
-
Figure 3—variant M1, circular weld nugget, the diameter and the height of the connector ϕ = 6 mm and h = 0.2 mm respectively
-
Figure 6—variant M6, two circular weld nuggets in the system of serial welds (2 × ϕnugget = 6.0 mm)
-
Figure 7—variant M8, two circular weld nuggets in the system of parallel welds (2 × ϕnugget = 4.24 mm)
-
Figure 8—variant M9, non-overlap (butt) joint, (S = 28.26 mm2)
6 Overview of results
-
Shear force (FS) in the static tensile test in relation to eleven analysed variants, i.e. various configurations, shapes and dimensions of the welded joint (Fig. 10);
-
Relative percentage shear force for variants M2 through M11 in relation to reference variant M1 (Fig. 11);
-
Shear force in relation to high [H] and low [L] parameters in the function of weld nugget diameter (Fig. 12);
-
Shear force and shear strength (Rt) in the function of weld nugget diameter in relation to the reference weld (variant M1) (Fig. 13).
7 Results of comparative analysis
7.1 Analysis in relation to various weld shapes
No. | Welding parameters | Welding current | Welding time (time of current flow) | Force | Weld nugget diameter | Energy | Indent depth | Shear force |
---|---|---|---|---|---|---|---|---|
kA | ms | kN | mm | kJ | mm | kN | ||
1 | High | 10 | 160 | 3.0 | 6.0 | 2.0 | 0.13 | 8.46 |
2 | Low | 7 | 410 | 1.5 | 6.0 | 2.8 | 0.10 | 8.10 |
7.2 Analysis of various weld nugget diameters
8 Results of experimental validation
No. | Variant no. | Welding current | Welding time | Force | Weld diameter | Joint (weld) area | Remarks | Additional information | Shear force Fs | Relative shear force (E2) | Shear strength (R t) | Relative shear strength (E2) |
---|---|---|---|---|---|---|---|---|---|---|---|---|
kA | ms | kN | mm | mm2 | kN | % | MPa | % | ||||
0 | E1 | – | – | – | – | 28.26 | Base material | Non-overlap joint; specimen width 18.84 m (S = 28.26 mm2) | 8.2 | – | 289 | – |
1 | E2 | 9.0 | 200 | 2.7 | 6.0 | 28.26 | Reference variant | 1 weld | 7.0 | 0.0 | 248 | 0.0 |
2 | E3 | 9.0 | 200 | 2.7 | 6.0 | 28.26 | Shearing | 2 serial welds (strength per 1 weld) | 7.35 | 5.0 | 260 | 5.0 |
3 | E4 | 9.0 | 190 | 2.7 | 4.7 | 17.34 | Peeling | 1 weld (smaller diameters) | 6.4 | − 8.6 | 369 | 49.0 |
4 | 9.0 | 180 | 2.7 | 4.1 | 13.20 | Shearing | 1 weld. (smaller diameters) | 5.7 | − 18.6 | 432 | 74.4 | |
5 | 9.0 | 160 | 2.7 | 3.9 | 11.94 | Shearing | 1 weld. (smaller diameters) | 4.0 | − 42.9 | 335 | 35.2 |
9 Discussion on experimental test results
10 Comparison of the results obtained in the FEM calculations and in the experimental tests
11 Concluding remarks
-
The experimental test results coincided with the numerical calculation results. Maximum differences between the FEM calculation results and the experimental test results of approximately 12% and 15% related to the maximum shear force and shear strength, respectively.
-
Adopting the highest value of the shear strength in the static tensile test as the primary criterion, the most favourable variants were M8 and M6 (2 circular weld nuggets, ϕ = 4.24–6.0 mm). In the first case, shear strength increased in relation to two welds having a smaller weld nugget area and the total area equal to the reference weld area; the shear strength in relation to this joint was higher by 21% than that related to the reference variant.
-
The results presented in the paper imply that the adopted criterion of the weld nugget diameter equal to five square roots of sheet thickness was not the most favourable. Bearing in mind the highest shear strength, it would be necessary to verify the selection criterion of the weld nugget diameter in relation to sheet thickness. As regards the above-presented aspect, the most favourable recommendations are those specified by the AWS (American Welding Society).
-
Variant M6 revealed that the reduction of the angle between the weld plane and the direction of the tensile force action led to an increase in the shear strength of the joint. The angle became smaller when welds were arranged in series, in the direction of the tensile force action. In terms of variant M6 it was possible to observe an increase in tensile force of approximately 5%. Very similar results, including an increase in shear force by 5%, were obtained in the experiment.
-
As expected, a significant increase in strength in relation to the weld having a non-circular nugget was not obtained. The square weld nugget (variant M3) was characterized by strength similar to that of the weld having the circular nugget (variant M1).
-
In the rectangular weld nugget having the longer side parallel to the direction of the tensile strength action (also referred to as the longitudinal narrow weld nugget), it was possible to observe an increase in shear strength of more than 4% (variant M5). Similar to variant M6, the above-named increase could be ascribed to the reduction of the angle between the weld plane and the direction of the tensile force action.
-
The ideal weld-related tests also involved the analysis of the variant which was not an overlap joint. The sheet cross-sectional area was equal to the nominal weld area, whereas the shear force was higher by 16%. However, the above-presented case was not applied in the overlap welding of sheets and was subjected to analysis only for comparative purposes.
-
The calculations revealed that in the tensile test it was necessary to try and reduce the angle between the weld plane and the direction of shear force action. Positive results were observed in cases of (1) variant M5, i.e. the rectangular weld nugget—longer side parallel to the direction of the tensile force effect; and (2) variant M6, i.e. the serial system of welds in the direction of the tensile strength action.
-
The calculations and laboratory tests performed to determine the numerical model of the ideal weld were considered mostly in terms of quality. The tendencies in the tests confirmed the functionality of the model proposed by the authors. Future work on the subject should be focused on the detailed determination of the properties of ideal weld numerical model, including an aspect related to the accuracy of results.