Enhancing the performance of cryogenic tanks through the modified co-bonding technique
Topic(s) : Material science
Co-authors :
Rita RIBEIRO (PORTUGAL), Bernardo ROCHA (PORTUGAL), Joana F. GUEDES (PORTUGAL), Rodrigo PINTO CARVALHO (PORTUGAL), Raquel M. SANTOSAbstract :
The ongoing pursuit of optimizing performance in aerospace technologies has challenged the scientific and industrial communities to reduce the total weight of space vehicles and maximize payload capacity. In this regard, the tanks are simultaneously a crucial part of the space vehicle propulsion system and one of the main contributors to their total weight. To make the tanks lighter, material selection is crucial and composite materials naturally become a popular choice. Compared to traditional materials like metallic alloys, composite materials have high strength-to-weight ratios, are corrosion-resistant, and offer design flexibility, making them particularly advantageous.
Nowadays, tanks made entirely of carbon fibre-reinforced polymers (CFRP) can be regarded as state-of-the-art. However, developing tanks using these materials requires overcoming challenges associated with their operating conditions — bi-directional stresses at cryogenic conditions. Knowing the mechanical behaviour and permeability properties at these conditions is key to properly designing a linerless cryogenic tank. , There exist various linerless (type V) tank designs, which depending on the dimensions can be made using dissolvable mandrels, collapsible or segmented tooling. The linerless cryogenic tank recently developed by INEGI, involves an inner layer combined with a reinforcement outer layer (both using CFRP). Firstly, an internal shell (reassembling a conventional mandrel) is produced using automated fibre placement and a collapsible mandrel, which is then reinforced and finished using filament winding. The same thermoset composite material is used in both stages. This leads to a situation in which the inner shell undergoes two curing cycles, which might compromise the performance of the tank due to sub-optimal bonding between both layers.
In this work, the modified co-curing is analysed as a strategy to potentially address the bonding between the pre-cured internal shell and the reinforcement shell. This technique consists of modifying the first curing process such that it becomes partially cured, and has proven to be effective in improving the bonding between CFRP parts. This concept is studied here in the context of cryogenic conditions. Firstly, differential scanning calorimetry (DSC) measurements were carried out to establish a relationship between the curing parameters and the laminate's curing degree. Then, the bonding properties were measured through mechanical testing of the interface. Intermediate curing levels were considered in this analysis, along with the total and uncured curing of the first laminate. The experimental campaign consisted of testing the samples at room temperature and after being subjected to cyclic cryogenic thermocycling, by immersing them in liquid nitrogen. The modified co-cured samples are compared with the directly co-bonded (one part is pre-cured) and co-cured samples (both parts are cured together).
Nowadays, tanks made entirely of carbon fibre-reinforced polymers (CFRP) can be regarded as state-of-the-art. However, developing tanks using these materials requires overcoming challenges associated with their operating conditions — bi-directional stresses at cryogenic conditions. Knowing the mechanical behaviour and permeability properties at these conditions is key to properly designing a linerless cryogenic tank. , There exist various linerless (type V) tank designs, which depending on the dimensions can be made using dissolvable mandrels, collapsible or segmented tooling. The linerless cryogenic tank recently developed by INEGI, involves an inner layer combined with a reinforcement outer layer (both using CFRP). Firstly, an internal shell (reassembling a conventional mandrel) is produced using automated fibre placement and a collapsible mandrel, which is then reinforced and finished using filament winding. The same thermoset composite material is used in both stages. This leads to a situation in which the inner shell undergoes two curing cycles, which might compromise the performance of the tank due to sub-optimal bonding between both layers.
In this work, the modified co-curing is analysed as a strategy to potentially address the bonding between the pre-cured internal shell and the reinforcement shell. This technique consists of modifying the first curing process such that it becomes partially cured, and has proven to be effective in improving the bonding between CFRP parts. This concept is studied here in the context of cryogenic conditions. Firstly, differential scanning calorimetry (DSC) measurements were carried out to establish a relationship between the curing parameters and the laminate's curing degree. Then, the bonding properties were measured through mechanical testing of the interface. Intermediate curing levels were considered in this analysis, along with the total and uncured curing of the first laminate. The experimental campaign consisted of testing the samples at room temperature and after being subjected to cyclic cryogenic thermocycling, by immersing them in liquid nitrogen. The modified co-cured samples are compared with the directly co-bonded (one part is pre-cured) and co-cured samples (both parts are cured together).