## 1 Introduction  
As one of the three major grains in China, wheat is prone to breakage and damage due to collisions, transportation, extrusion, vibrations, impacts, and other factors [1]. Broken grains can cause various problems, such as changes in taste, nutrient loss, and even mold growth. At present, [PERSON] [2], [PERSON] [3], [PERSON] [4], and other cases mainly studied the crushing of wheat grain under different moisture contents. But these studies are all based on physical crushing tests; there is no specific study on the form of wheat-grain crushing, which could not accurately reflect the process of wheat-grain crushing. [PERSON] [5] obtained relationships between shear force values and physical parameters, such as protein content and bulk density, by placing two electronic universal testing machines in different positions but did not analyze the mechanical crushing characteristics of wheat when broken. [PERSON] [6] observed rice stress cracking and damage phenomenon through scanning electron microscopy, but scanning electron microscopy could only observe the stress crack in rice when broken at a static moment and could not dynamically display cracks during the rice crushing process. [PERSON] [7] studied the relationships between different placement methods and the critical load of wheat through a finite-element method. However, the wheat model was simplified as an ellipsoid, which had low accuracy and could not accurately represent the external characteristics of the wheat grain and the specific situation of its crushing. [PERSON] [8] and [PERSON] [9] obtained seed models of barley and wheat through three-dimensional scanning technology and studied the crack location and crushing process during the crushing process. However, the filling particles were relatively small, the accuracy was not high, and no scientific design method was adopted.  
The discrete-element method was initially employed in mechanical fields such as rock mechanics and subsequently extended to various sectors including agriculture, food, and chemical industries. In recent years, it has found extensive applications in agricultural engineering, grain storage, and related areas [10; 11; 12]. With continuous advancements and refinements in the discrete-element method, the discrete-element software EDEM has gained widespread adoption. It is now extensively employed to investigate the mechanical properties of crops through simulation experiments [13; 14]. Currently, the calibration of model parameters using EDEM software mainly relies on the measurement of the angle of repose for various crops, including soybean [15], rice [16], corn [17], spinach main-root [18], and rape stalk [19]. This parameter serves as a key indicator for evaluating and refining the simulation models. However, most of these calibration parameters are contact parameters, and there is less calibration for bonding parameters. [PERSON] [20], [PERSON] [21], and [PERSON] [22] calibrated the binding parameters of cornstalk, but their discrete-element simulation models were relatively simple and not accurate enough.  
This paper mainly establishes an accurate model of wheat grain through CT scanning, which is a prerequisite for establishing a simulation model of wheat fragmentation in the future. Then, taking the critical load of wheat-grain crushing as the target value, the single-factor test, the Plackett-Burman test, the steepest-climbing test, and the Box-Behnken test are designed for bond parameter calibration. Eventually, the optimal calibration parameters are obtained to provide the parameter basis for studying the internal crushing characteristics of wheat grain.