Research And Its CAD Applications Of Constitutive Model Of Cushioning Packaging Materials

Expanded polypropylene (EPP) foam for its advantages of good energyabsorption, excellent recoverability from repeated shocking and deformations,environmental friendly, high service temperature, light weight, dimensionalstability, has become an increasingly important material in the segments ofindustry, automobile and packaging. Therefore, study on static and dynamicmechanical properties of EPP has mostly practical significance that providingdata used in the design of cushioning packaging.Static constitutive equation for expanded polypropylene (EPP) was derivedby using compression test performed on pressure testing machine YE-50, with aninput of three different combinations of density and strain ratio. The parametersconsidered density dependent. Dynamic constitutive equation based on staticconstitutive equation was also studied. The parameters added the effects of strainratio were further subjected to recognition analysis.Shock test with the purpose to obtain the maximum acceleration-staticstress curves was performed on different densities, drop height, thicknessesunder different static stress. In addition, we exemplified the application ofG m σ_scurves in packaging design of certain cabinet with the method of“six-step” cushioning packaging design. Also, the prototype sample was madeand tested. Comparative analysis of several modified cushioning design theorieswas developed to overcome drawbacks of “six-step” method. Dynamic shockconstitutive equation was proposed as the basis of data testing by DY-3testmachine. The response acceleration andG_m σ_scurves under different thicknessand static stress can be fitted by using a set of experimental acceleration data.The curves fitting well with experimental data can be effectively used to reducetesting times. In this thesis,1stopt, a new tool that being used widely in nonlinearparametric recognition, optimization, differential equations solving wasintroduced. Its simple and practical programming language can greatly helpengineers overcome the obstacles on mathematics. Meanwhile, simplified dynamic shock constitutive equation related to shape function and strain rationwas established, and the equation was further subjected to curve fitting andparametric recognition.The application of compression constitutive equation in packaging designwith the model proposed was studied. Comparing the result calculated bytraditionalG_m σ_smethod, the result needing more material was over-packaging.Using ANSYS LS-DYNA to simulate the EPP drop test by DY-3test machinewith the fitting stress-strain data obtained by static compression constitutiveequation as loading curve, we found that comparing the experimental result ofacceleration, the error of simulation result was less than10%, it showed that thefitting data derived by static compression constitutive equation can not onlyovercome the inaccuracy simplified EPP as a linear material, but also avoidexperiment to obtain the loading curve.Using graphic programming LabVIEW to develop cushioning packagingdesign software was studied at the basic of theory and experiment described bythe previous section. Function that automatically calculating the cushioning area,thickness was developed for the cushioning design. The cushioning packagingdatabase was established based on some experiment and calculation. The userscan design the packaging with different materials and density by calling thecorresponded data in the database. An extended function of database was added,users can add their own testing data of certain packaging materials, expandingmaterials in the database. Users inputting cushioning material, product basicinformation, the software can automatically calculate the target, which can helpsome engineers without testing conditions, and greatly improve the efficiency ofdesign cycle.