Developing crack resistant polymer composite matrices for liquid hydrogen storage

随着国际社会努力在2050年前实现净零排放，航空业正在竞相在未来几十年内采用零碳排放的燃料来源。人们普遍认为，液氢(LH2)，一种储存在20K(-253摄氏度)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。然而，与向液氢过渡相关的许多挑战将是航空业需要克服的。一个重大挑战是LH2在飞机上的储存。虽然金属坦克目前用于航天工业的一次性LH2运载火箭，很可能是民用航空市场上的第一辆；碳纤维增强聚合物(CFRP)坦克提供了显著的重力效率效益，在坦克的多周期20-25年寿命期间，这意味着相当大的成本节约。尽管CFRP储罐被认为是很有前途的长期储存容器，但聚合物基质在极低温度下对微破裂的敏感性目前是采用的主要障碍。微裂纹在这种应用中有许多问题，尤其是与氢渗透增加相关的安全和热问题，还包括正在受到损害的储罐的完整性，以及在裂缝网络中液氢沸腾导致分层或储罐破裂的机会。据了解，低温下的基体微裂纹是通过几种可能的机制形成的热致残余应力造成的。在微观层面上，纤维和基体之间的热膨胀系数(CTE)的不匹配导致了热循环过程中两个组分中的残余应力。在结构层次的下一层次上，不同纤维取向的相邻层之间的有效CTE不匹配是可能的原因。此外，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。这也可能导致产生瞬时热诱发应力，进而导致微裂纹。因此，该项目的总体目标是开发一种聚合物复合材料基质，它可以承受在20K低温环境中的反复暴露，而不会出现微裂纹，并适用于LH2储罐。为了解决这一问题，该项目的主要目标包括：-通过设计实验测试方法，确定哪种聚合物分子特性或增韧方法能够使具有所需热机械和物理特性的母体抑制微裂纹-设计和合成新母体或调整现有材料以结合这些材料特性或增韧方法-对这些母体材料进行表征，以验证设计过程和随后使用最佳候选者制造复合板-设计和进行严格的测试活动，以表征LH2储罐的关键性能指标，如微裂纹断裂韧性、氢渗透性和在重复低温循环下的抗裂性

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