3. Results and Discussion
When the ball collides with the plate material, the inelasticity parameter (
) between the two and force time during the impact change owing to different material properties. The Zener collision theory equation was numerically analyzed and complex calculations were performed. Furthermore, the force–time collision curve diagram was drawn with
at 0, 0.5, 1.0, and 1.5, as shown in
Figure 4a.
Figure 4a shows the process of change in the impact contact time and the magnitude of the contact force. Through the Hertzian contact force as a function of the displacement (Equation (26)), the impact force was converted to material displacement and other parameters. Next, the material inelasticity parameter (
) was calculated using Equation (29).
Boettcher et al. [
12] revised the nonlinear motion equation (Equation (25)) [
2] proposed by Zener with a dimensionless parameter,
, to be adjusted (determined by adapting the
dimensionless analytical displacement–time function), and Hertz’s equation (Equation (26)) [
1], and established a method that simply analyzes the nonlinear motion equation of the Zener collision [
3,
12]. Boettcher et al. also simplified the Zener nonlinear collision equation (Equation (28)) to a linear differential equation, which can be regarded as a damped oscillation equation. When
, an ideal elastic collision without damping is indicated, whereas
is an inelastic collision and has a damping state [
12]. The process obtains the force–time impact curve of
, which is a perfect elastic collision equation, and then adjusts
to obtain
, that is, the inelastic collision [
3,
12].
Figure 4b shows the normalized impact force curve obtained by Boettcher et al. after a simplified analysis of Zener’s nonlinear motion equation [
12]. This work is based on the nonlinear motion equation provided by Zener [
2], which establishes the force–time collision curve equation in different ways.
As observed in
Figure 4, the sphere collides with the plate, and the contact force changes with time. Additionally, the force ascends from zero to the maximum value and then decreases gradually. It is considered to be an ideal elastic collision when the inelasticity parameter is zero. The impact process is not affected by the friction force and causes energy attenuation. Consequently, the force–time variation curve is a symmetrical graph. When the inelasticity parameter is larger (
), it is an inelastic collision. Energy loss was generated during the collision between the sphere and the plate, and the contact force was smaller, while the contact time was longer. As seen in
Figure 4, the force–time collision curve based on Equation (28) correlates well with the dimensionless displacement (
) and time (
). As shown in
Figure 5, the force–time curve is a graph of the quadratic function. First, we used the approximation method, and the curve was drawn based on Equation (30).
The relationship between the elastic collision time (
τ) and the inelasticity parameter (
) of the plate is based on the equation
provided by Müller et al. [
4]. Additionally, the displacement (
) can be converted into force using Equation (26). Equation (30) provides the left–right symmetrical quadratic function graph. When the elasticity parameter is 0, it is an elastic collision curve. Consequently, the inelasticity parameter value (
) and impact force are greater and the contact time is longer, as shown in
Figure 5.
However, in the actual collision process,
. After the sphere collides with the plate, the force on the plate shows an exponential attenuation as the sphere leaves the plate. Therefore, we multiply the
in Equation (30) by
to obtain Equation (31), as
Equation (31), as seen from
Figure 6a, shows an exponential decay change with time in the force process of different inelasticity parameter materials. The selection range of
coefficient is from
to
. When multiplied by
, the force is an attenuated process of the contact time. As per the comparison curve between
Figure 6b and the
of Equation (30) multiplied by
and
Figure 4a, Zener’s standard force–time collision curve is the closest.
Figure 6b shows that
, and the maximum collision force (
) is not equal to 1. Therefore, the correction Equation (31), multiplied by
, aims to correct the change in contact time and force of different inelasticity parameters, and the force (
) of
can be corrected to 1, as shown in
Figure 7a.
The force–time collision curve of Equation (32) is quite close to the original Zener force–time diagram (
Figure 4), as shown in
Figure 7a. However, when the inelasticity parameters are 1 and 1.5, the maximum force curve is very different from the Zener curve; hence, we multiply the
in Equation (32) by
to modify the same, as shown in Equation (33).
When the
of Equation (32) is multiplied by
, the force–time curve with n > 0 and
does not change, as shown in
Figure 7b–d. However, when the value of n in Equation (33) becomes larger, and
, the impact force curve gradually becomes smaller, whereas for
, it gradually becomes larger, as shown in
Figure 7b–d. Additionally, the value of n gradually increases from 1.0, 1.3, and 1.5 for comparison. Finally, the value of
is the maximum force peak value of the force–time curve drawn using Equation (33) established in this study is between the peak force value of the inelasticity parameter 0.5 to 1.5 and the Zener value, and the peaks of the force–time curve are equidistant, as shown in
Figure 7c.
As shown in
Figure 7c, the force–time curve peak values of the inelasticity parameters 0.5–1.5 are approximately equidistant from the Zener force–time curve peak values. Therefore, the correction Equation (33) adjusts the peak force of the force–time curve and multiplies it by
to provide Equation (34).
When
,
, n is any value, the force is 1, and the force–time curve remains constant. Thus, the inelasticity parameter is between 0.5 and 1.5. When the value of n in Equation (34) is larger, the force–time curve of the inelasticity parameter gradually increases the force value, as shown in
Figure 8. When
, it is nearly identical to the time–force curve of the original Zener, and the curve drawn with inelasticity parameters of 1–1.5 uses Equation (34). Therefore,
is the most suitable. As shown in
Figure 9a,b, the force–time collision curve given using Equation (34) and that given by Boettcher et al. are different from the analytical methods that provide graphs and equations that are considerably similar to the diagrams of the force–time collisions proposed by Zener.