Developing crack resistant polymer composite matrices for liquid hydrogen storage

随着到2050年实现净零排放的国际努力，航空业正在竞相在未来几十年内采用零碳排放燃料。人们普遍认为，液氢（LH 2），一种储存在20 K（-253 ℃）的低温液体，将作为大多数飞机市场的燃料来源，因为它提供了更好的有效载荷和替代解决方案，如电池或气态氢。尽管如此，航空业仍需要克服与向液氢过渡相关的许多挑战。一个重大挑战是飞机上储存液氢。虽然金属贮箱目前在航天工业中用于一次性液氢2运载火箭，并可能首先在民用航空市场上销售，但碳纤维增强聚合物贮箱具有显著的重量效率效益，在贮箱20-25年的多周期寿命中，这意味着节省了大量成本。虽然CFRP罐被认为是有前途的长期储存容器，但聚合物基质在这些极低温度下对微裂纹的敏感性是目前采用的主要障碍。在这种应用中存在许多微裂纹问题，不仅是与增加的氢渗透相关的安全和热问题，而且还有罐的完整性受到损害以及裂纹网络内的液氢汽化的可能性，从而导致分层或罐破裂。低温下的基体微裂纹被认为是由热致残余应力通过几种可能的机制累积而引起的。在微观层面上，纤维和基体之间的热膨胀系数（CTE）的不匹配导致在热循环期间两种成分中的残余应力。在结构层次的下一个层次上，具有不同纤维取向的相邻层之间的有效CTE的不匹配是一个可能的原因。除此之外，当冷却到低温时，材料可能会通过不均匀的温度分布经历热冲击，其中相邻区域遇到不同的温度，从而在材料上产生陡峭的温度梯度。这也可能导致瞬态热致应力的发展，进而导致微裂纹。因此，该项目的首要目标是开发一种聚合物复合材料基体，该基体可以承受反复暴露于20 K低温环境而不会产生微裂纹，并适用于LH 2储罐。为解决这一问题，该项目的主要目标包括：- 通过实验测试方法的设计确定，所述聚合物分子性质或增韧方法使得具有所需热机械和物理性质的基质能够抑制微裂纹-设计和合成新基质或改造现有材料以结合这些材料性质或增韧方法-对这些基体材料进行表征，以验证设计过程和随后使用最佳候选材料制造复合板-设计并进行严格的测试活动，以验证复合材料在液氢储罐关键性能指标方面的性能，例如微裂纹断裂韧性，在反复低温循环下的氢渗透性和抗开裂性

With the international effort to reach Net Zero by 2050, the aviation industry is in a race to adopt zero-carbon emission fuel sources within the coming decades. It is widely accepted that liquid hydrogen (LH2), a cryogenic liquid stored at 20 K (-253 degrees celsius), will serve as this fuel source for the majority of the aircraft market, as it offers a better payload and range to alternative solutions such as batteries or gaseous hydrogen. Nevertheless, there are many challenges associated with the transition to liquid hydrogen that the aviation industry will need to overcome. One significant challenge is the storage of LH2 aboard the aircraft. While metallic tanks are currently used in the space industry for single-use LH2 launch vehicles and are likely to be first to market in civil aviation; carbon fibre reinforced polymer (CFRP) tanks offer significant gravimetric efficiency benefits which, over the multi-cycle 20-25-year lifetime of a tank, translates to considerable cost savings. While CFRP tanks are considered promising long-term storage vessels, the susceptibility of the polymer matrix to microcracking at these extremely low temperatures is currently a primary barrier to adoption. There are a number of issues with microcracking in this application, not least the safety and thermal issues associated with increased hydrogen permeation, but also the integrity of the tank being compromised and the chance of liquid hydrogen boil off within crack networks causing delamination or tank rupture. Matrix microcracking at cryogenic temperatures is understood to be caused by the build-up of thermally induced residual stresses through several possible mechanisms. On the microscopic level, the mismatch of co-efficient of thermal expansion (CTE) between the fibre and matrix leads to residual stresses in both constituents during thermal cycling. On the next level of structural hierarchy, the mismatch of effective CTE between adjacent plies with varying fibre orientation is a possible cause. In addition to this, when cooled down to cryogenic temperatures a material can experience thermal shock via inhomogeneous temperature distributions, where neighbouring domains encounter different temperatures, creating a steep temperature gradient across the material. This can also result in the development of transient thermally induced stresses and in turn cause microcracking. The overarching aim of this project is therefore to develop a polymer composite matrix which can withstand repeated exposure to a 20 K cryogenic environment without microcracking and be suitable for use in LH2 storage tanks. To address this, the key objectives of this project include: - Determine, through a design of experiments testing approach, which polymeric molecular properties or toughening methods enable matrices with the desired thermomechanical and physical properties to supress microcracking - Design and synthesise new matrices or adapt existing materials to incorporate these material properties or toughening methods - Characterisation of these matrix materials to validate the design process and subsequent manufacture of composite panels using the best candidates - Design and conduct a rigorous testing campaign to characterise the composite materials with respect to the key performance indicators for LH2 tanks, such as microcrack fracture toughness, hydrogen permeability and resistance to cracking under repeated cryogenic cycling