本文選題：BWK復合材料 + 有限元分析　； 參考：《東華大學》2015年碩士論文

【摘要】：雙軸向經編針織物(biaxial warp-knitted,簡寫為BWK)在經編地組織襯入伸直紗線，經編組織使襯入紗線形成穩(wěn)定結構，沿紗線方向具有高拉伸剛度和強度。雙軸向經編針織物可作為增強體用于風力發(fā)電、航空航天等領域。本課題以壓縮試驗為基礎，建立細觀結構簡化模型，利用有限元方法研究雙軸向經編針織復合材料壓縮性能，分析破壞機理。 論文主要工作有： (1) BWK復合材料沖擊壓縮試驗：采用MTS-810材料測試系統(tǒng)和分離式霍普金森壓桿完成BWK復合材料不同應變率范圍內的沖擊壓縮試驗，獲取應力-應變曲線、破壞形態(tài)特征。試驗結果表明：BWK復合材料對應變率敏感，最大應力和壓縮剛度隨應變率增大而增大，失效應變隨應變率增大而減�。籅WK復合材料厚度方向失效模式為剪切破壞，面內方向準靜態(tài)時失效模式為剪切破壞，高應變率時材料主要是分層破壞。 (2) BWK復合材料細觀結構模型的簡化：經編紗的力學性質融進樹脂內，簡化為“等效樹脂”。依據BWK的結構特點，確定等效樹脂最小代表體積單元(RVE)，將RVE分割成一系列纖維體積含量相同的“亞單胞”，計算局部坐標系下“亞單胞”剛度矩陣，并轉換成全局坐標系下“亞單胞”剛度矩陣，，根據體積平均思想計算得到等效樹脂的剛度矩陣，簡化后BWK復合材料只包含等效樹脂與經緯紗。在有限元軟件ABAQUS中創(chuàng)建BWK復合材料細觀結構簡化模型。 (3)有限元計算結果分析：在商用有限元軟件ABAQUS中模擬BWK復合材料準靜態(tài)壓縮和高應變率沖擊壓縮破壞過程。模擬結果與試驗結果吻合較好，證明本文所建有限元細觀結構簡化模型在預測壓縮性能方面有效。通過觀察應力波在經緯紗和樹脂中的傳播，揭示復合材料破壞機理：BWK復合材料面外壓縮失效模式為剪切破壞，產生兩條與壓縮軸成45°夾角的剪切帶，切斷與剪切帶不在一個平面上的纖維束，樹脂也沿著剪切帶開裂。復合材料被分割成三部分發(fā)生滑移，導致較大塑性變形。面內方向上失效模式主要是分層破壞。應力由受壓面向另一端面?zhèn)鬟f，纖維束間樹脂首先發(fā)生碎裂，層間發(fā)生分離。主要由纖維束承受壓縮載荷，纖維束發(fā)生屈曲變形使復合材料產生分層。
[Abstract]:The biaxial warp knitted fabric (biaxial warp-knitted, BWK) is lined with straight yarns in the warp knitted structure, the warp knitting organization makes the lining into the yarn to form a stable structure, and has a high tensile stiffness and strength along the yarn direction. The dual axis warp knitted fabric can be used as an augmented body for wind power generation, aerospace and other fields. This subject is based on compression test. Based on the foundation, a simplified microstructure model is established. The compressive properties of the biaxial warp knitted composites are studied by using the finite element method, and the failure mechanism is analyzed.
The main work of the paper is as follows:
(1) the impact compression test of BWK composite material: using MTS-810 material test system and separated Hopkinson pressure bar to complete the impact compression test within the range of different strain rate of BWK composite, and obtain the stress strain curve and destroy the shape characteristics. The test results show that the BWK composite material is sensitive to the variation rate, the maximum stress and the compression stiffness follow. The strain rate increases and the failure strain decreases with the increase of strain rate; the failure mode of the thickness direction of BWK composite is shear failure. When the direction of the surface is quasi static, the failure mode is shear failure, and the material is mainly stratified failure when the high strain rate is high.
(2) simplification of the meso structure model of BWK composite: the mechanical properties of warp knitting yarn are incorporated into the resin and simplified as "equivalent resin". According to the structural characteristics of BWK, the minimum representative volume unit (RVE) of the equivalent resin is determined, and RVE is divided into a series of "subcells" with the same volume content of the fiber, and the "sub cell" in the local coordinate system is calculated. The degree matrix is converted into the "subcellular" stiffness matrix in the global coordinate system, and the stiffness matrix of the equivalent resin is obtained by the volume averaging method. The simplified BWK composite only contains the equivalent resin and the warp and weft yarn. The meso microstructure simplification model of the BWK composite is created in the finite element software ABAQUS.
(3) analysis of the results of finite element calculation: Simulation of BWK composite quasi-static compression and high strain rate impact compression failure process in the commercial finite element software ABAQUS. The simulation results are in good agreement with the experimental results. It is proved that the simplified model of the finite element structure in this paper is effective in predicting the compression performance. The propagation of the yarn and resin reveals the failure mechanism of the composite material: the failure mode of the BWK composite is shear failure, which produces two shear bands with the angle of 45 degrees with the compression axis, cutting off the fiber bundles that are not on the one plane, and cracking the resin along the shear zone. The composite material is divided into three parts to slip and lead to the slip. The failure mode in the direction of the surface is mainly stratified failure. The stress is transferred from the compression to the other end, the resin is first cracked and the interlayer separates. The fiber bundle is mainly subjected to the compression load, and the fiber bundle flexed to make the composite layered.
【學位授予單位】：東華大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：TB332

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