Mechanism of restraining maize stalk block springback under pressure maintenance/strain maintenance

Chopped corn straw with a low density needs to be compressed and compacted, thereby improving the utilization rate of straw for transportation, storage, and subsequent utilization. However, the chopped corn straw is viscoelastic materials that can rebound to a large extent after compression, which can affect the compression effect. Previous studies reported that the pressure and strain maintenance can effectively reduce the rebound of straw after compression, but a specific mechanism in detail is lacking to clarify the confusion in practice. This study aims to reveal the mechanism of pressure and strain maintenance how to inhibit the rebound of straw after compression, optimize the straw compression process, and further improve the dimensional stability of straw block after compression. Taking the chopped corn straw as the test material, a compression test was carried out to investigate the effects of pressure and strain maintenance characteristics on the dimensional stability of straw blocks under various compression conditions, such as the moisture content, the maximum compression stress, and feeding mass. The results showed that both pressure and strain maintenance significantly increased the dimensional stability coefficient of straw after compression, but there were different mechanisms for restraining the rebound of straw. A mechanism of pressure maintenance resistance to the rebound of straw: The relative rebound displacement was reduced whether to increase the compression shift or to reduce the rebound displacement, thereby increasing the dimensional stability coefficient of compressed straw. The essence was to maintain a certain pressure to further compress the straw, where the viscoelastic strain in the compressed straw was under high pressure. In this situation, the irreversible strain increased in the compressed straw. The strain maintenance reduced the residual stress in straw after compression, where the relaxation rate after 30 s of strain maintenance was more than 30%, and the relaxation rate after 150 s of strain maintenance was about 40%, indicating that the relaxation rate in the first 30 s accounted for 80% of the 150 s relaxation rate in total. A mechanism of strain maintenance was obtained to inhibit the rebound of straw after compression. It was essential to reduce the viscoelastic stress in the straw block after compression. Specifically, a feasible way is to relax the viscoelastic resilience for the reduction of strain in straw, thereby increasing the dimensional stability coefficient of straw after compression. A comparison was made on the effects of pressure and strain maintenance on the stability under various compression conditions. In the chopped corn straw, the pressure maintenance for 150 s increased the dimensional stability coefficient of the compressed straw by 1.52 percent point-4.26 percent point, whereas, the strain maintenance for 150 s increased by 4.36 percent point -6.78 percent point. Both stabilization processes significantly inhibit the rebound of compressed straw, but under the same compression condition, there was always a better effect of strain maintenance than pressure maintenance. The finding can provide an sound reference for the pressing molding for other biomass and straw with small particle size. The results of this study can also offer an essential basis on the development of technology and equipment for the compression baling and cold pressing molding of chopped corn stalk.