2 Theoretical modeling of the first impact buffering performance
The theoretical basis for the establishment of corrugated board liners is based on the three-dimensional differential constitutive equations of nonlinear viscoelastic-plastic materials. Based on the basic characteristics of the corrugated paperboard cushioning properties in the literature, the nonlinear model for the corrugated board at the time of the first impact is established as follows:
In order to reflect the stress-strain curve, a sine term is introduced in the equation, a negative stiffness occurs in a small strain range, and a tangent term is introduced in order to reflect the part where the stress rises sharply with an increase in strain. According to the acceleration data of the mid-stroke test, the optimization method of the complex method is used to identify the objective function in the model parameters ai and b1o optimization design methods:
According to the identified model parameter values, according to the dynamic numerical calculation of the model, the acceleration curve, velocity curve and displacement curve of the triple corrugated cardboard material under the impact of a 10 cm height drop impact are shown in FIG. 2 .
It can be seen from Fig. 2 that the buffering performance of the model is in accordance with the basic characteristics of the cushioning performance of the triple corrugated cardboard material based on the experimental test data, that is, the three basic characteristics of the relationship among the drop height, material thickness and acceleration peak. . However, due to the failure to consider the influence of the acceleration waveform, there are certain errors in the acceleration, velocity, and displacement waveforms of the theoretical model, and it cannot reflect the characteristics of plastic deformation and impact damage of the material, and cannot be shown in the continuous impact process. Significant differences in the dynamic characteristics of one stroke and subsequent impacts, as well as the effects of temperature, humidity and deformation types. For this purpose, a nonlinear viscoelastic-plastic model of corrugated cardboard with multiple impacts needs to be established.
3 Conclusion
Three basic characteristics of corrugated board's cushioning performance are summarized from the experimental curves. Based on the nonlinear viscoelastic-plastic model of corrugated board liners, the nonlinear viscoelastic-plastic model parameters of multilayer corrugated cardboard are identified by using the measured data.
For the first time, the six-parameter nonlinear model of mid-stroke can reflect the basic characteristics of the cushioning performance of corrugated cardboard, but it does not consider the influence of plastic deformation, impact frequency and damage characteristics during the compression process of corrugated cardboard, and basically reflects multilayer corrugated cardboard. Dynamic characteristics during continuous multiple impacts.
(Author/Liu Hao Gaode Harbin University of Commerce, Zhejiang University of Technology)
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