Fatigue and damage tolerance of 3D-woven composites

最近，3D编织复合材料在航空航天、船舶、汽车和可再生能源等工程应用中得到了广泛的应用。这类复合材料提供了几个经济和性能优势，超过他们的层压同行和金属合金。三维机织复合材料通常制备成近净形的预成型件，然后注入树脂并固化以形成最终结构。这种生产方法消除了与层压复合材料的铺叠或与使用昂贵的预浸材料相关的成本。此外，3D机织复合材料还具有一些关键的机械性能优势，如更高的损伤容限，以及更好的抗冲击和抗分层性。由于3D机织复合材料的主要应用领域涉及冲击，因此有必要开发建模能力，以捕捉冲击事件后的疲劳寿命等行为。纺织复合材料的疲劳性能不如层压结构的疲劳性能好。为此，该项目旨在深入了解3D编织复合材料的疲劳和损伤容限。这将通过实验表征和高保真度建模相结合来实现。研究表明，小规模损伤（例如，基体开裂和脱粘）在低载荷下在3D编织复合材料中开始。由于这些材料对损伤的高耐受性和重新分布应力的能力，这种细观损伤不会影响静态负载条件下3D编织结构的机械性能，并且只能使用先进的无损检测（NDT）技术检测。然而，当受到增加的载荷水平和循环疲劳载荷时，细观尺度损伤进展，降低刚度，并最终导致材料的最终失效。该项目的主要兴趣是这些材料在循环疲劳载荷下的细观损伤的进展。低速冲击试验增加了一定程度的不确定性和可变性，在循环疲劳加载之前引入试样的损伤水平。这使得几个冲击后疲劳测试很难以相同的损伤水平开始。相反，使用缺口试样可确保更可测量和可重复的损伤水平。因此，实验测试的第一部分将集中在缺口3D编织复合材料。然后将进行含有预引发的细观尺度损伤的3D机织复合材料的疲劳测试。他们的目的是深入了解在循环疲劳载荷下3D编织复合材料的损伤进展情况。为此，先进的无损检测和成像技术（例如，CT扫描、声发射等）将被雇用。这种理解将有助于发展一个高保真度的模型，能够预测细观尺度的损伤进展在疲劳载荷下的三维编织复合材料。然后将根据实验数据验证该模型。在本项目中，考虑了细观尺度，因为一些研究人员已经表明，纺织复合材料中细观损伤的发展和进展可以以合理的精度进行建模。然而，相关的高计算成本，禁止在结构尺度上的损伤建模。因此，该项目的最终目标是将开发的疲劳模型与更大的宏观分析工具相结合，以便能够在结构尺度上预测3D编织复合材料部件的疲劳寿命。鉴于上述情况，该项目的主要目标和目的可以总结如下：-包含预引发细观损伤的三维编织复合材料的疲劳测试。在细观尺度上开发高保真疲劳模型。在结构尺度上预测三维机织复合材料疲劳寿命的模型能力的扩展。

Recently, 3D woven composite materials are seeing wide use in engineering applications such as aerospace, marine, automotive and renewable energy sectors. This category of composites provides several economic and performance advantages over their laminated counterparts and metal alloys. 3D woven composites are usually prepared in near net-shape preforms before being infused by resin and cured to form the final structure. This production method eliminates the costs associated with layup of laminated composites or with use of expensive prepreg materials. Additionally, 3D woven composites provide some key mechanical performance advantages such as higher damage tolerance, as well as better impact and delamination resistance.Since the main area of application for 3D woven composites involves impact, it is necessary to develop modelling capabilities that can capture behaviour such as fatigue life after impact events. The fatigue behaviour of textile composites is less well understood than for laminated structures. To this end, this project aims to develop a deep understanding of the fatigue and damage tolerance of 3D woven composites. This will be achieved via a combination of experimental characterisation and high-fidelity modelling.Research has shown that small scale damage (e.g., matrix cracking and debonding) initiates in 3D woven composites at low loads. Due to these materials' high tolerance to damage and the ability to redistribute stresses, this meso-scale damage doesn't affect the 3D woven structure's mechanical performance under static loading conditions and is only detectable using advanced Non-Destructive Testing (NDT) techniques. However, when subjected to increased load levels and cyclic fatigue loading, the meso-scale damage progresses, reduces the stiffness, and will ultimately lead to the material's final failure. The main interest of the project is the progression of meso-scale damage in these materials under cyclic fatigue loading post-impact. Low-velocity impact tests add a certain level of uncertainty and variability in the level of damage introduced into the specimen prior to cyclic fatigue loading. This makes it difficult for several post-impact fatigue tests to start with the same level of damage. Conversely, the use of a notched specimen ensures a level of damage which is more measurable and repeatable. Therefore, the first part of the experimental testing will focus on notched 3D woven composites. Fatigue testing of 3D woven composites containing pre-initiated meso-scale damage will then be carried out. Their purpose is to gain a deep understanding of how damage progresses in 3D woven composites under cyclic fatigue loading. To this end, advanced NDT and imaging techniques (e.g., CT scanning, acoustic emission, etc.) will be employed. This understanding will help the development of a high-fidelity model capable of predicting meso-scale damage progression in 3D woven composites under fatigue loading. This model will then be validated against the experimental data. In this project, the meso-scale level is considered because several researchers have shown that the development and progression of meso-scale damage in textile composites can be modelled with reasonable accuracy. However, the associated high computational cost prohibits the modelling of damage at structural scales. Therefore, this project ultimately aims to combine the developed fatigue model with larger, macro-scale analysis tools, to be able to predict the fatigue life of 3D woven composite components at the structural scale. In view of the above, the key aims and objectives of this project can be summarised as follows:- Fatigue testing of 3D woven composites containing pre-initiated meso-scale damage.- Development of high-fidelity fatigue model at the meso-scale.- Extension of model capability to predict fatigue life of 3D woven composites at the structural scale.