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Chaobang hot melt glue for bookbinding

July 18, 2019

Glue bonding is a composite connection technology combining resistance spot welding (or projection welding) technology with glue bonding [1], which has been widely used in the aerospace, aerospace and automotive industries. For example, the airframe, flaps, fuel tanks, and low-altitude support fighter jets of a transport aircraft have adopted a welding process [2]; China's research and development work in this area has also made progress [3].

The study of the mechanical behavior of the welded structures has received extensive attention from scholars at home and abroad. There have been many experiments and numerical analysis work on single-welded lap joints [4,5]. However, there are few studies on the impact of joint spacing on structural mechanical behavior in multiple joint structures. Solder joint pitch is an important geometric parameter in the design and manufacture of adhesive structures. The reasonable choice of solder joint pitch can enable the welded structure to meet the requirements for economical production and reliability of use. Therefore, the finite element numerical analysis method and experimental research method are used in this paper to study the single-row multi-welded spot welding heads. When two kinds of adhesives with different elastic moduli are used, the stress-strain fields and fractures in the joints are measured by the distance between the solder joints. The effect of intensity.

1 joint shape size and finite element mesh

1.1 The shape and size of the joint

The dimensions of a single-row, multi-weld, spot-welded lap joint are shown in Figure 1. Both ends of the specimen were subjected to uniform tensile shear loads. The base metal is 08Al automotive deep drawing steel plate, 40mm wide and 1mm thick. In order to investigate the effect of the elastic modulus of the adhesive on the distribution of stress and strain in the joint, a high elastic modulus epoxy resin-based adhesive and a low elastic modulus acrylate adhesive were used, and the thickness of the adhesive layer was 0.4 mm. The length of the joint lap zone is 40mm, and the 5mm diameter solder joints are arranged along the Y direction at equal distances. In this study, five kinds of solder joint distances of 10mm, 20mm, 30mm, 40mm and 50mm were selected to study the stress-strain distribution in two types of solder joints.

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Fig.1 Shapes and dimensions of single-column multiple-welded test specimens (mm)
Fig.1 Shape and size of weldbonded
Specimen with single row multi-spot

1.2 Finite Element Meshing of Joints

For the multi-welded spot welding head shown in Fig. 1, when the Y direction of the test piece is very long, under the uniform tensile shearing action, the force conditions of the solder joints in the joint are the same, and at the same time, because of a certain solder joint about X The direction of the line is symmetrical, so you only need to consider half of them. Fig. 2 shows the finite element meshing of the test piece when the solder joint pitch is a=40mm. At this time, the total width of the mesh Y is 20mm. Using three-dimensional eight-node block units, the upper and lower plates and the adhesive layer are divided into two layers, and the grids are subdivided at the edges of the solder joints and the overlapping area. The minimum size in the grid is 0.15 mm. In the analysis, the welded joints of the welded joints were simplified, and it was considered that the structural joints were in good condition. There was no defect on the interface between the adhesive layer and the parent metal, and the influence of the electrode indentation was not taken into account. In the calculation model, the heterogeneity of the mechanical properties of the solder joint area is taken into account. It is considered that the nugget and the base metal have different mechanical properties. Since the range of the heat affected zone is small, it is assumed that it has the same mechanical properties as the nugget in the calculation. The mechanical properties of the materials in the calculation model are listed in Table 1. A bilinear stress-strain curve was used to describe the elasto-plastic properties of the material. ALGOR nonlinear finite element structural analysis program was used to calculate the stress and strain fields in each joint under nominal stress of 135MPa.

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Fig. 2 Finite element meshing of specimens (a) Overall finite element meshes; (b) Finite element meshes in overlapping areas
Fig.2 Finite element meshes of global specimen(a) and finite element meshes of lap zone(b)

Table 1 Mechanical properties of materials used in finite element analysis
Table1 Mechanical properties of materials used for finite element

Material elastic modulus
E /MPa Poisson's ratio
V Yield strength σ y /MPa Hardening modulus
E t /MPa shear modulus
G/GPa Base metal 190000 0.25 160 2000 76 Nugget 200000 0.20 600 1800 83.34 Epoxy adhesive 2875 0.42 90 500 1.06 Acrylic adhesive 50 0.45 40 40 1.72 E-2
2 Distribution of stress and strain in soldered joints

2.1 Glue joints of epoxy-based adhesives

The calculation results show that the stress and strain are similar in the solder joints under the five solder joint pitches. For the sake of clarity, only stress and strain distributions of a=10mm, 30mm and 50mm are given. Fig. 3 shows the distribution of stress and strain in the adhesive layer in the X-direction near the bonding surface between the steel plate and the adhesive layer in the three joints using the high elastic modulus epoxy resin adhesive.

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Fig. 3 Stress and strain distributions in the bonding area of epoxy joints with different solder joint pitches (a) Normal stress; (b) Shear stress; (c) Positive strain; (d) Shear strain
Fig.3 Stress-strain distribution in the region of weldbonded
Joint with different spot pitch and epoxy resin adhesive
(a) normal stresses; (b) shear stresses; (c) normal strains; (d) shear strains

It can be seen from the distribution of the normal stress σ x in the X direction in the overlapping region in Fig. 3a that the distribution of normal stress in the joints of the three solder joint pitches is basically the same. The stress in the solder joint area is much higher than the normal stress in the adhesive layer. There is no normal stress at the edge of the solder joint. The center of the solder joint has the highest normal stress; the stress in the adhesive layer is almost evenly distributed, and it rises slightly at the left and right edges of the overlap area. With the increase of the solder joint pitch, the normal stress inside the solder joint decreases slightly, and the normal stress value in the solder layer does not change substantially.

The distribution of the shear stress τ zx in the X direction in Fig. 3b shows that there are shear stress concentrations at the edge of the weld in each joint, the right edge is the tensile shear stress peak, and the left edge is the compressive shear stress peak; the shear stress in the overlapped layer is presented The distribution trend of the large margin and the small central area is the largest in the area around the left and right edges of the overlapping area. The peak values of tensile and compressive shear stress at the edge of the solder joint decrease with the increase of solder joint pitch; the maximum shear stress near the edge of the solder joint area does not change with the increase of solder pitch.

The distribution of positive strain ε x is shown in Figure 3c. It can be seen from this that the positive strain in the entire overlapping area is very small. The positive strain in the adhesive layer is greater than the solder joint area, and the positive strain of the right adhesive layer in the overlap region is higher than the left side. Near the edge of the solder joint and the adhesive layer at the edge of the overlap region, the positive strain value is relatively high, and the positive strain value near the right edge of the overlap region is the highest. The maximum positive strain at the edge of the overlap region increases slightly with the increase of the solder joint pitch.

Figure 3d shows the distribution of shear strain ε zx . The visible shear strain value is significantly higher than the positive strain value. The distribution of shear strain in the overlap region is small in the center and large in the edge, indicating that the shear strain is mainly distributed in the adhesive layer region, the shear strain in the solder joint region is small, the shear strain is not concentrated at the edge of the solder joint, and the shear strain inside the solder joint is evenly distributed. The distance a between solder joints increases from 10mm to 50mm, the shear strain distribution trend in the overlapping area does not change, and the shear strain value of the edge layer of the overlap area increases slightly.

This analysis shows that when high elasticity modulus adhesives are used, the solder joint pitch is increased within 10 to 50 mm, the stress in the solder joint area is reduced, and the stress strain in the adhesive layer at the edge of the overlap region is only slightly increased. The bearing capacity of the joint will not be significantly reduced. At this time, the use of larger solder joint spacing to reduce the number of solder joints is of positive significance for power saving and productivity improvement.

2.2 Acrylic adhesive adhesive welding head

Figure 4 shows the distribution of stress and strain in the adhesive layer in the X-direction in the three joints with 10mm, 30mm and 50mm joints with low elastic modulus.

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Fig. 4 Distribution of stress and strain in lap joints of acrylate adhesive solder joints with different solder joint pitches
(a) normal stress; (b) shear stress; (c) positive strain; (d) shear strain
Fig.4 Stress-strain distribution in the lap region
Of weldbonded joint with different spot pitch and acryl resin adhesive
(a) normal stresses; (b) shear stresses; (c) normal strains; (d) shear strains

It can be seen from the distribution of the normal stress σ x in Fig. 4a that similar to the high elastic modulus adhesive joints, there is a high normal stress at the solder joints, and the normal stress in the adhesive layer is very small; the difference is that at the time of the solder joint edges There is a normal stress concentration, the right edge is the tensile normal stress peak, and the left edge is the compressive normal stress peak. The peak stress at the edge of the solder joint increases with the increase of the solder joint pitch, and the normal stress in the adhesive layer does not change with the change of solder pitch.

The distribution of shear stress τ zx in the overlap region is shown in Figure 4b. The shear stress is also mainly distributed in the solder joint area, and the shear stress in the adhesive layer is close to zero. The shear stress is concentrated at the two edges of the solder joint, and the two shear stress peaks are close to each other. The shear stress inside the solder joint and at the edge of the solder joint increase with the increase of the solder pitch, and the shear stress in the solder layer does not change with the change of solder pitch.

The distribution of positive strain ε x is shown in Figure 4c. There is a positive strain concentration at the edge of the weld, a positive strain at the right edge and a compressive positive strain at the left edge. Both the tensile and compressive positive strain peaks at the edges of the solder joints increase with the increase in solder pitch. The positive strain in the adhesive layer at the right edge of the overlap region is slightly higher than that in the middle adhesive layer of the overlap region, and the strain value does not change substantially with the increase in the pitch of the solder joint.

The distribution of the shear strain ε zx in the X direction in Fig. 4d shows that the shear strain in the overlapping area is mainly distributed in the adhesive layer. The shear strain at the joint is much smaller than the shear strain in the adhesive layer, and the shear strain is substantially evenly distributed within the joint. . The shear strain in the gel layer gradually increases from the edge of the solder joint to the edge of the overlap region and reaches the maximum at the edge of the overlap region. The shear strain in the adhesive layer of the entire overlapped area increases with the increase of the solder pitch.

From the above analysis, it can be seen that when low-modulus acrylate adhesives are used, the normal stress and shear stress are concentrated at the solder joints, and the stress concentration increases with the increase of the pitch of the solder joints; shear in the edge layer of the overlap area The strain value also increases with the distance between solder joints. Acrylic adhesive solder joints mainly bear the load of solder joints, the solder joint pitch increases, corresponding to the reduction of the number of solder joints at the same board width, will inevitably increase the stress value at the solder joint; at the same time, the rigidity of the solder joint also follows the solder joint. The decrease of the point decreases, the deformation resistance of the joint decreases, and the shear strain increases. There is an adverse effect on the strength of the joint.

3 Single-row multiple-welded dispensing heads

In order to investigate the influence of the distance between solder joints on the mechanical properties of single-row and multiple-distribution solder joints, and to examine the validity of numerical analysis, a static tensile shear test was conducted using the CSS-1110 electronic universal testing machine. The test was conducted at room temperature. The loading rate is 5mm/min. The solder joint spacing a is 20mm, 30mm and 40mm, respectively. Each test piece contains 3 solder joints. The Y-direction length of the corresponding test piece is 60mm, 90mm and 120mm, respectively.

The first load peak of each joint obtained by the test corresponding to the rupture of the glue layer is shown in Figure 5a. Obviously, due to the large width of joints with large solder joint pitches, the breaking load is high. In order to ignore the influence of the board width factor, Figure 5b shows the relationship between the nominal stress σ n and the distance between solder joints when the joint is broken. The nominal stress σ n is defined as:

1 (1)

Where P f is the breaking load, I is the width of the plate, and t is the thickness of the plate. From Fig. 5b, it can be seen that the nominal stress at the break of the joint slightly decreases with the increase of the solder joint pitch. Hills [6] also studied the fracture behavior of a plurality of solder joints with different solder joint pitches and different number of solder joints, and tested the test pieces with different solder joints of the same width. The results show that when a high elastic modulus adhesive is used, the fracture load of the adhesive layer of the joint increases with the increase of the number of solder joints, that is, the nominal stress at the time of cracking of the adhesive layer increases with the decrease of the solder joint pitch, and the low elasticity is used. This effect is even more pronounced in the case of adhesives. This conclusion is consistent with the experimental results we obtained. It is also consistent with the predictions we obtained from the numerical calculation results, which shows the correctness of the calculation results. It can be seen that the finite element numerical analysis method is an effective method for studying the influence of geometric parameters on the mechanical behavior of joints.

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Fig. 5 Breakage load and nominal stress at different solder joint pitches (a) Relationship between breakage load and solder joint pitch;
(b) Relationship between nominal stress at break and solder joint pitch
Fig.5 Fracture load and nominal stresses of adhesive layer
For different spot pitch (a) fracture load vs spot pitch;
(b) nominal fracture vs spot pitch

4 Conclusion

(1) When high elastic modulus adhesives are used, the distance between solder joints is increased within 10 to 50 mm, the stress in the solder joint area is reduced, and the stress strain in the adhesive layer at the edge of the overlap region is slightly increased, increasing the solder joints. Spacing will reduce the load carrying capacity of the joints, but not much.

(2) When low-modulus acrylate adhesives are used, stress concentration occurs at the solder joints, and the stress concentration increases with the increase of solder pitch; the shear strain in the edge layer of the overlap area also varies with the solder joint pitch. The increase increases. Increasing the solder joint pitch reduces the number of loaded solder joints and reduces joint stiffness, which has an adverse effect on joint strength. This effect is more pronounced than when high elastic modulus adhesives are used.

(3) In a single-row multi-joint joint using an epoxy-based adhesive, the adhesive layer first fractured. The large solder joints with large solder joint spacing have high fracture load due to the large specimen width, but the nominal stress of joint fracture decreases slightly with the increase of solder joint pitch.

(4) The effect of the distance between solder joints on the strength of joints is consistent with the predicted law based on numerical analysis, which proves the validity of the prediction of joint mechanical behavior using numerical methods.

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