Elsevier

Biosystems Engineering

Volume 206, June 2021, Pages 135-149
Biosystems Engineering

Research Paper
Sugarcane stem cut quality investigated by finite element simulation and experiment

https://doi.org/10.1016/j.biosystemseng.2021.03.013Get rights and content

Highlights

  • Internal and external cut quality factors examined by simulation and experiment.

  • Finite element numerical simulations verified by real cutting test.

  • Optimum settings determined by orthogonal experiment and verified by test.

  • Lower cutting forces benefit good quality cutting.

  • Damage mechanism of stem explained by numerical simulations.

Previous studies on the cut quality of sugarcane stalks have mainly focused on external factors. However, the effects of internal factors on the cut quality have rarely been studied. In this study, the influence of internal and external factors on the cut quality were considered. Numerical finite element simulations and an experimental design were utilised to investigate the influences of the internal and external factors on the cut quality. The numerical model was validated using experimental cutting tests and based on a theoretical analysis. The optimum combination of cutting system parameters was investigated using an orthogonal test. The cut quality of the optimal combination was verified based on experiments. From the results, it was seen that the cutting bevel angle plays a significant role in affecting the cutting force, whereas machine forward speed (within the range 0.4–0.6 m s−1) and rotational speed (within the range 650–750 rpm) had no noticeable influence on cutting force. The optimal combination obtained by the orthogonal experiment was a cutting bevel angle of 30°, forward speed of 0.4 m s−1, and cutter rotational speed of 650 rpm. The optimised parameter combination produced an improved quality of cut in a cutting test. The damage mechanisms of sugarcane arising from internal factors were also investigated. This study provides basic information for the design of a base cutter for sugarcane harvesting.

Introduction

At present, research on mechanised sugarcane harvesting mainly focuses on two aspects, i.e., the energy consumption and cut quality (see Fig. 1). Mathanker, Grift, and Hansen (2015) investigated the influences of the cutting speed and blade oblique angle on the cutting energy with an impact type cutting mechanism, and found that the specific cutting energy increases with the cutting speed. Wang, Ma, Ke, Xing, and Bai (2020) examined the cutting energy consumption for cutting stalks and found that the rotational speed of the base cutter and sugarcane feeding rate had significant effects on the energy consumption during cutting, whereas the tilt angle of the base cutter and the number of blades mounted on the base cutter had no noticeable effects. In addition to investigations of cutting energy consumption, more attention is being paid to cut quality in mechanised harvesting. To establish mechanised harvesting of sugarcane in hilly areas, many difficulties remain to be solved but one is reduced cut quality from stalk damage during harvesting relative to manual harvesting (Xie, Wang, Cheng, Zeng, & Yang, 2018). Stalk damage can result in sugar loss and/or deterioration in juice quality (Ma et al., 2016). Sugarcane is generally cut by the impact of a rotating disc with multiple cutting blades (Mello & Harris, 2003). The contact forces and stresses accumulate, and a stress pattern is established inside the stalk until failure conditions are reached under the continued motion of the knife (Chattopadhyay & Pandey, 1999). Therefore, the factors affecting the stalk cut quality include both external and internal factors. In this study, “external causes” refers to the motion parameters and the structural parameters of the base cutter, whereas “internal causes” refers to the mechanical properties of the stalk and movements and stress wave propagations that occur during the cutting process.

Several studies have focused on the external factors affecting cut quality. Momin et al. (2017) found that the blade design of the base cutter had an influence on sugarcane cut quality, and they provided guidelines for optimal blade configurations. The major factors causing cane damage in the process of mechanical harvesting were investigated by Xie et al. (2018), aiming to reduce harvesting losses. Using cutting height as a quality indicator, Salvi et al. (2007) studied the performance of a base cutting machine. A series of laboratory-based cutting tests were conducted using a smooth-edge blade, and it was observed that the cane stalks were split or broken instead of being cut when the cutting disc speed was 22.0 m s−1 or less (Liu et al., 2007a). Yang et al. (2007) investigated the effects of the base cutter vibration frequency and amplitude on the stubble damage, and obtained a positive correlation between the stubble damage and the frequency and amplitude of the base cutter vibration. This indicated that stubble damage could be reduced by modifying the structure of the base cutter to reduce the vibration. Different blade and disc combinations for the base cutter mechanism were compared, and it was found that tilted cutting blades produced the lowest damage levels, and that serrated blades and normal discs produced the best cutting height (de Toledo et al., 2013). Zhang et al., 2017 investigated the effects of a contra-rotating base cutter on cut quality using a quadratic regression revolution design. They observed that the stubble damage rate of the contra-rotating base cutter was lower than that of a conventional base cutter. Thanomputra and Kiatiwat (2016) believed that a blade wears down rapidly under the actions of impacts with the ground and rocks, leading to stalk damage, and increasing the energy requirements. A non-contact cutting method (a waterjet) has been tested for sugarcane cutting research. The results showed that waterjet cutting has potential, but also revealed some weaknesses. At present, there are no reports of the application of waterjets in commercial sugarcane cutting.

Compared to studies on the external factors affecting cut quality, there are relatively fewer studies considering the internal factors of the stalk. Liu et al. (2004) studied the damage to sugarcane stalks under bending loads using a three-point bending method. However, this approach was not employed in a real cutting process, leading to only limited damage prediction for the stalk during the real cutting process. In general, very little is known regarding the internal causes of stalk damage during cutting. Moreover, there are some studies that attempt to explain the damage mechanisms by utilising the useful information can be extracted from numerical simulations.

Rectangular blades are frequently used to cut sugarcane (Fig. 2a). This type of blade employs an impact cutting principle that originated from manual sugarcane cutting. The sugarcane stalk tends to crack from impact with the blade. In one study, a trapezoidal-shaped knife with a specified cutting angle based on a principle of sliding cutting was utilised in the design of a sugarcane harvester (Fig. 2b). Nevertheless, the side cutting edge of the trapezoidal knife design was the first to lodge in the stalk, demonstrating that the sliding cutting angle did not play a major role in cutting. As the movement advanced, it gradually became more apparent that the turn of the main cutting edge was what severed the cane. There are also additional studies on using traditional blades for stem cutting (Mathanker et al., 2015; Ma et al., 2016; Momin et al., 2017; Yang, Zhao, Liu, Chen, & Yang, 2021). However, studies on the cutting processes of arc blades and on their cut quality, especially those based on the finite element method, remain limited. Thus, an arc blade was chosen in this study. It has only a major arc edge, and does not have a side edge (Fig. 2c).

Overall, cut quality remains a problem to be solved. The present research approach is mainly to explore the rule(s) regarding cut quality through physical experiments. However, physical experiments require considerable time and cost. Moreover, the duration of time for cutting an individual cane is very short. It is therefore difficult to clearly observe the cutting process when the base cutter is in a working state. However, numerical simulations can compensate for the deficiencies of testing. The LS-DYNA multi-physics simulation software package is an explicit nonlinear dynamic analysis program, and is capable of simulating a variety of real–world complex nonlinearities, material nonlinearities, and contact nonlinearities that has been used to investigate a variety of cutting problems with finite element models established based on different tool angles and cutting speeds. The process of sugarcane cutting was simulated using LS-DYNA (Huang, Wang, Tang, Zhao, & Kong, 2011) and Yang, Yang, Liu, Liang, and Mo (2011) built a dynamic simulation model for a soil-sugarcane cutting machine system, and conducted a dynamic simulation experiment using LS-DYNA. Meng, Wei, Wei, Chen, and Cui (2019) studied a circular saw blade cutting system for a small mulberry cutting machine using LS-DYNA, and obtained the best working parameters for the circular saw blade cutting system. Yang et al. (2021) explored the forces acting on blade surfaces and roots based on LS-DYNA. Thus, it has shown that various contact problems can be effectively simulated using LS-DYNA, and that phenomena that are difficult to observe in physical experiments can be investigated.

In view of the above, the purpose of this study is to examine the effects on cut quality from combinations of internal and external factors, using numerical simulations and an experimental design (see Fig. 1). The objective was to validate the numerical model against the experimental results, optimise the parameter combination for the cutting system using an orthogonal experiment and then conduct a cut quality using the optimum combination. Moreover, the damage mechanisms of the stalk, that is, the internal factors, were also to be investigated. Thus the overall aim of this study was to provide a foundation for the optimisation and improvement of sugarcane harvesters.

Section snippets

Model development

The structural parameters of the model are listed in Table 1. To establish a proper physical model and reduce computational time, the model of the cutting system was simplified into four blades and the sugarcane stalk (see Fig. 3a). Thus, this cutting device structure was simple; an actual cutting system is often a more complex construction, with a wide array of components and transmission systems. Accordingly, so as to reduce the computational load of the simulation, features such as the drive

Optimisation of parameters and analysis of stem damage mechanism

Using the simulation techniques presented above, a dynamic cutting process for sugarcane was developed and examined in this study. To obtain the optimal parameter combination of the cutting force, an orthogonal simulation test was conducted. Variance analysis was used to determine whether the factors had significant effects on the cutting force. Finally, the optimal parameter combination was obtained through the above analysis.

Conclusions

The cut quality of sugar cane was examined considering internal and external factors using numerical simulations and experiments. The optimal parameter combination for the cutting force was investigated based on an orthogonal test. The cut quality under the optimal combination was examined. The damage mechanisms of the sugarcane were also considered. The findings and conclusions of the present study are summarised as follows.

  • (1)

    Within the ranges of the selected parameters, the cutting bevel angle

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

This work was supported by the National Natural Science Foundation of China, China (grant number 61763001), Science Foundation of Guangxi University of Science and Technology, China (grant number 174517). The authors sincerely acknowledge the members of the research team for their help.

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