Bending properties of three-dimensional honeycomb sandwich structure composites: experiment and Finite Element Method simulation

Abstract

This paper fabricated three-dimensional (3D) honeycomb sandwich structure fabrics with three different cross-section shapes on an ordinary loom by reasonable design with low cost. The 3D honeycomb sandwich structure composites were fabricated by the vacuum assisted resin transfer molding process. Then, the bending properties of 3D honeycomb sandwich structure composites with different cross-section shapes were tested. The results showed that the 3D honeycomb sandwich structure composite with a hexagonal cross-section shape had the maximum load, the 3D honeycomb sandwich structure composite with a triquetrous cross-section shape had the minimum load and the 3D honeycomb sandwich structure composite with a quadrangular cross-section shape had a load between the two. The bending failure mode showed that the 3D honeycomb sandwich structure composite had a typical bending failure mode with compression failure in the front and tensile failure in the back. Finally, the load–displacement curves and failure mode were obtained by FEM (Finite Element Method) simulation with ABAQUS software. The good agreements of comparisons proved the validity of the FEM.

Keywords

three-dimensional woven fabric honeycomb composite bending properties failure mode Finite Element Method simulation

Honeycomb three-dimensional (3D) textile structural composites were fabricated with honeycomb 3D textile fabrics used as the reinforced phase and resin used as the matrix phase. Most ordinary honeycomb composites were pressed with plate material, and the processing method was simple, but the integrity of the ordinary honeycomb composites was poor and it was easy to crack.^1,2 Compared with ordinary fabrics, 3D honeycomb sandwich structure fabrics have many advantages such as large thickness, large stiffness, small mass, transformable cross-section shapes(square, rhombus, sine curve, hexagon, etc.) and so on.^3–5 In view of these advantages, honeycomb 3D textile structural composites have drawn more and more attention and could be widely used in aerospace, automobile, shipbuilding, construction, storage, pipeline and other fields.

In weaving, Tianjin Polytechnic University¹ wove a new fabric by combining a honeycomb structure and weaving principle on a dobby rapier loom or jacquard rapier loom. Dong⁶ changed the crimping device and let-off mechanism to study honeycomb 3D integrated fabrics. Liu et al.⁷ fabricated 3D honeycomb sandwich structure fabric with basalt fiber yarns on a CSW053 computer controlled loom. Zhu et al.⁸ prepared 3D sandwich woven fabric with a hexagonal cross-section shape on an ordinary loom. Nie and He⁹ put forward the sub-organizations concept in the design of multi-layer woven fabric and quickly and accurately drew the organization chart of multi-layer woven fabric using this method. Chen et al.¹⁰ indicated the basic concept, design and weaving method of honeycomb 3D integrated fabric. At present, the 3D honeycomb sandwich structure fabric has been fabricated by a dobby rapier loom or an improved loom, but the weaving process is tedious and the cost of production is high. In addition, there are no detailed processing parameters for fabricating 3D honeycomb sandwich structure fabric on an ordinary loom. Lv et al.¹¹ wove honeycomb and T-shaped 3D integrated woven fabrics on an ordinary loom, the results of which laid a certain foundation for this paper.

Huang et al.¹² studied the shear properties of a six-layer honeycomb 3D woven composite, and they were compared with those of the laminated plates. Zhu et al.^13,14 tested the impacting performance of honeycomb 3D woven composites with glass fiber and polyester fiber, the results of which showed that the energy absorption was different from the different fiber volume content. Lai et al.¹⁵ explored the effects of stitching parameters on the flexural properties of the composites and the results revealed that the failure of the structure was mostly due to core shear failure. Raju et al.¹⁶ studied the mechanics performance of honeycomb sandwich composites under low-speed impact and analyzed the failure modes. However, the mechanics performance, failure mechanism and failure mode of 3D honeycomb sandwich structure composites should be further explored. Lv et al.¹⁷ studied the mechanical properties of 3D woven basalt fiber composite materials with experiments and the Finite Element Method (FEM). Then this also laid a certain foundation for this paper.

Three-dimensional honeycomb sandwich structure fabrics of three different cross-section shapes were fabricated on an ordinary loom by reasonable design with low cost. We used 600 tex glass fiber filaments tows as warp yarns and 2000 tex basalt fiber filaments tows as weft yarns. The 3D honeycomb sandwich structure composites were fabricated by the vacuum assisted resin transfer molding (VARTM) process. Then, the bending properties of 3D honeycomb sandwich structure composites with different cross-section shapes were tested. Finally, the load–displacement curves and failure modes were obtained by FEM simulation with ABAQUS software.

Experimental details

Experimental materials and equipment

E-glass fiber filament tows (600 tex) were employed as warp yarns and 2000 tex basalt fiber filaments tows were employed as weft yarns. Vinyl ester resin was used as the matrix. Methyl ethyl ketone peroxide was used as the solidification reagent and cobalt naphthenate was used as the promoter. The loom for weaving a small sample in the lab (Y100S) was used, the VARTM system was used for molding, a universal system prototype (NHY-W) was used for cutting samples and a microcomputer control electronic universal testing machine (RGT-5) was applied for testing.

Design and weaving of 3D honeycomb sandwich structure fabrics

Design of 3D honeycomb sandwich structure fabrics

Three-dimensional honeycomb sandwich structure fabric belongs to the multi-layer binding weave. The warp structural drawings of 3D honeycomb sandwich structure fabrics with three different cross-section shapes are shown in Figure 1. The chain drafts of 3D honeycomb integrated woven fabrics with three different cross-section shapes were drawn up according to the warp structural drawings and they are shown in Figure 2.

Figure 1.

Warp structural drawings of three-dimensional honeycomb sandwich structure fabrics with three different cross-section shapes. Note: the line indicates warp yarn and the dot indicates weft yarn.

Figure 2.

Chain drafts of three-dimensional honeycomb sandwich structure fabrics with three different cross-section shapes.

Weaving of 3D honeycomb sandwich structure fabrics

The weaving parameters of 3D honeycomb sandwich structure fabrics are shown in Table 1. In order to make the same thickness of three different 3D honeycomb sandwich structure composites, the weaving parameters were different. In addition, the weaving parameters were as similar as possible to ensure equal thickness of the fabric. For the same thickness, the load–displacement curves could be compared.

Table 1.

Weaving parameters of three-dimensional honeycomb sandwich structure fabrics

	Triquetrous cross-section shape		Quadrangular cross-section shape		Hexagonal cross-section shape
	Basalt fiber filaments tows	E-glass fiber filaments tows	Basalt fiber filaments tows	E-glass fiber filaments tows	Basalt fiber filaments tows	E-glass fiber filaments tows
Linear density/tex	2000	800	2000	800	2000	800
Layer number of yarns	14	7	12	6	12	6
Density of warp and weft/(root/10 cm)	80	315	95	270	104	270

Fabrication of 3D honeycomb sandwich structure composites

VARTM was used to prepare 3D honeycomb sandwich structure composites. In addition, the role of its principle and the structure of each part can be seen in the literature.¹⁸ The proportion of vinyl ester resin, methyl ethyl ketone peroxide and cobalt naphthenate was 100:4:2. The unsaturated polyester resin were injected into the preform by the VARTM technique, and then consolidated in the condition of vacuum with the time of 60–90 min at normal temperature. Photographs of 3D honeycomb sandwich structure composites with warp cross-sections are shown in Figure 3. (The 3D honeycomb sandwich structure fabrics were filled with polyurethane foam in order to make good molding and the filled 3D honeycomb sandwich structure fabrics were prepared with vinylester resin, methyl ethyl ketone peroxide and cobalt naphthenate by VARTM.)

Figure 3.

Photographs of three-dimensional honeycomb sandwich structure composites.

Testing of 3D honeycomb sandwich structure composites

The testing of bending properties was carried out according to GB/T 9341-2008/ISO 178:2001 (the sample was 160 mm long and 30 mm wide), and the universal system prototype (NHY-W) was used to prepare testing samples, which were obtained from the composite in the weft direction. Then, the samples were tested on the microcomputer control universal testing machine (RGT-5). The testing speed was 2 mm/min. The schematic diagram of the three-point bending test is shown in Figure 4.

Figure 4.

Schematic diagram of the three-point bending test.

Results and discussion

Material property

The material properties of 3D honeycomb sandwich structure composites are shown in Table 2. These parameters were difficult to test. So, in this paper the parameters in Table 2 were not tested. However, we calculated and debugged them in ABAQUS software. The parameters in Table 2 were the most optimal to the results of FEM simulation with ABAQUS software and experiments.

Table 2.

Material properties of three-dimensional honeycomb sandwich structure composites

	E₁₁/GPa	E₂₂/GPa	E₃₃/GPa	ν₁₂	ν₂₃	ν₁₃	G₁₂/GPa	G₁₃/GPa	G₂₃/GPa
Triquetrous cross-section shape	35	6	6	0.25	0.25	0.2	2.78	2.78	2.4
Quadrangular cross-section shape	36.5	7	6.6	0.3	0.3	0.25	3.55	3.05	2.6
Hexagonal cross-section shape	39.6	7.7	7.1	0.3	0.3	0.3	3.82	3.05	2.62

Geometrical models and mesh models

The geometrical models of 3D honeycomb sandwich structure composites were set up according to actual specimens in the ABAQUS/Explicit dynamic finite element analysis module with the left-hand spiral rules. The C3D8R solid elements were used for meshing the geometrical model. The 3D honeycomb sandwich structure fabrics were filled with polyurethane foam in order to make good molding, so when we did FEM simulation, the polyurethane foam were filled into composites; the Young’s modulus resin of the polyurethane foam was 39.4 mpa and the Poisson’s ratio of the polyurethane foam was 0.42. The total number of mesh model elements with a triquetrous cross-section shape was 2304. The total number of mesh model elements with a quadrangular cross-section shape was 1376. The total number of mesh model elements with a hexagonal cross-section shape was 3584. The number of seeds in length, width and height in the geometrical model was 32, 6, and 4, respectively. The number of elements in both sides was the same. The solid element was C3D8R. The shapes of the elements were automatically generated by ABAQUS software. The mesh models of 3D honeycomb sandwich structure composites are shown in Figure 5.

Figure 5.

Mesh model three-dimensional honeycomb sandwich structure composites.

Load–displacement curve

The mean and variance of the maximum loads with experiments are shown in Table 3.

Table 3.

Mean and variance of the maximum loads

Type	First group/N	Second group/N	Third group/N	Mean/N	Average variance	Coefficient of variation
Triquetrous cross-section shape	5083	5051	5072	5068.7	13.3	0.26%
Quadrangular cross-section shape	5319	5333	5304	5318.7	11.9	0.22%
Hexagonal cross-section shape	6583	6603	6576	6587.3	11.3	0.17%

The experiment and FEM simulation load–displacement curves of 3D honeycomb sandwich structure composites are shown in Figure 6.

Figure 6.

Experiment and Finite Element Method simulation load–displacement curves of three-dimensional honeycomb sandwich structure composites.

From Figure 6, the results and trend of the curves of the experiments and FEM simulation were similar. So, this paper used the reasonable FEM with ABAQUS software to forecast the load–displacement curves of 3D honeycomb sandwich structure composites. The similar trend of the comparisons proved the validity of the FEM. The load–displacement curves could be divided into three phases. At the beginning, the load–displacement curves were almost linear. This indicated that the bonding situation was also good between the resin and the fiber. So, the materials exhibited linear elastic performance. The second phase was that the curves no longer presented straight lines and the slope of the curves was reduced. This was because the contact surface area was increasing between the samples and the cone with the increase of displacement. In addition, the resin began to be destroyed, and at this time the fiber bundles bore the main load as the reinforced materials and still had a lot of stress tolerance. The third phase was the descending branch. The fiber bundles and resin began to be damaged.

From Figure 6, the 3D honeycomb sandwich structure composites with a hexagonal cross-section shape had the maximum load, the 3D honeycomb sandwich structure composites with a triquetrous cross-section shape had the minimum load and the 3D honeycomb sandwich structure composites with a quadrangular cross-section shape had a load between the two. This could be because of the following. (1) Fibrous mass fraction (The fibrous mass fraction of the 3D honeycomb sandwich structure composites was achieved by the burning method. The specific steps were as follows: in the heating muffle, the minimum temperature was set 400℃, the highest temperature was set 600℃ and the honeycomb 3D integrated woven composites were heated for 3 h. Then, the resin was volatile and the 3D honeycomb sandwich structure fabrics were taken out. The mass difference value of 3D honeycomb sandwich structure composites and 3D honeycomb sandwich structure fabrics was divided by volume of the 3D honeycomb sandwich structure composites and this was the fibrous mass fraction.). The fibrous mass fraction of the 3D honeycomb sandwich structure composites with a hexagonal cross-section shape was 63.97%, the fibrous mass fraction of the 3D honeycomb sandwich structure composites with a quadrangular cross-section shape was 59.27% and the fibrous mass fraction of the 3D honeycomb sandwich structure composites with a triquetrous cross-section shape was 57.06%. (2) Cross-section area: when the cross-section area was larger, the stable performance of the 3D honeycomb sandwich structure composites was better. The cross-section area of the 3D honeycomb sandwich structure composites with a hexagonal cross-section shape was the maximum, the cross-section area of the 3D honeycomb sandwich structure composites with a triquetrous cross-section shape was the minimum and the cross-section area of the 3D honeycomb sandwich structure composites with a quadrangular cross-section shape was between the two. (3) Organizational structure of junction place: in this paper, for three different sections, each layer was made of a plain weave structure. However, the organizational structure of the junction place with a hexagonal cross-section shape was used for four sets of two weft-one warp-two weft, while the organizational structure of the junction place with a quadrangular cross-section shape was used for one set, and the organizational structure of the junction place with a triquetrous cross-section shape used a plain weave structure. This was seen in Figure 1.The organizational structures of the junction place of 3D honeycomb sandwich structure fabrics were different with different cross-section shapes.

Failure mode and failure mechanism

The results of three kinds 3D honeycomb sandwich structure composites were similar. So, we only used the 3D honeycomb sandwich structure composites with a triquetrous cross-section shape as an example. The overall and partial enlargement photographs and FEM stress nephograms of 3D honeycomb sandwich structure composites with triquetrous cross-section shape are shown in Figure 7.

Figure 7.

Overall and partial enlargement photographs and Finite Element Method (FEM) stress nephograms of three-dimensional honeycomb sandwich structure composites with a triquetrous cross-section shape.

From Figure 6, the results and trend of these curves of experiments and FEM simulation were similar. In addition, from Figure 7, the breaking forms and the place of experiments and FEM simulation were consistent. So, from Figures 6 and 7, the FEM models can accurately predicted the experimental results. We saw a good agreement of bending deformation and damage of 3D honeycomb sandwich structure composites with a triquetrous cross-section shape in Figure 7 between the experimental and FEM results, which proved the veracity of the finite element model. From Figure 7, the bending failure modes showed that the 3D honeycomb sandwich structure composites with a triquetrous cross-section shape were a typical bending failure mode with the compression failure in the front and tensile failure in the back. In addition, there was no delamination. Then, the bending failure modes of 3D honeycomb sandwich structure composites with a quadrangular cross-section shape and 3D honeycomb sandwich structure composites with a hexagonal cross-section shape were similar to 3D honeycomb sandwich structure composites with a triquetrous cross-section shape. Furthermore, the 3D honeycomb sandwich structure composite had high delamination resistance because no delamination was found.

Conclusions

Three-dimensional honeycomb sandwich structure fabrics with three different cross-section shapes were fabricated on and ordinary loom by reasonable design with low cost.

The 3D honeycomb sandwich structure composites had excellent mechanical properties. In the testing process, the materials showed good interlaminar shear strength, no delamination and no splitting phenomenon. In addition, the structure of the 3D honeycomb sandwich structure fabrics used as the reinforced materials was different, and the bending properties of composite materials made of 3D honeycomb sandwich structure fabrics also showed a large difference. The 3D honeycomb sandwich structure composites with a hexagonal cross-section shape had the maximum load, the 3D honeycomb sandwich structure composites with a triquetrous cross-section shape had the minimum load and the 3D honeycomb sandwich structure composite with a quadrangular cross-section shape had a load between the two.

This paper applied the reasonable FEM with the ABAQUS/Explicit dynamic finite element analysis module to forecast the bending properties of 3D honeycomb sandwich structure composites. The good agreements of the comparisons proved the validity of the FEM.

Footnotes

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship and/or publication of this article.

Funding

The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: The authors gratefully acknowledge financial support from the National Science Foundation of Liaoning Province (201602051).

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