Wang Fuwei,Zhu Shuhuan,Wei Mingdi,Luo Tianshen

(School of Mechanical and Electrical Engineering,North Minzu University,Yinchuan,750021)

Abstract:In this paper,the mechanical properties of fused-deposited 3D printed PLA levers were studied by experimental methods.Tension and compression tests were carried out on 3D printed levers of square grid with filling rate of 15%.The relationships between load and deformation,stress and strain were analyzed,and the elastic modulus,intensity limit,tension and compression stiffness and approximate poisson's ratio were calculated.The results show that there is obvious creep phenomenon in the tension process of 3D printed PLA levers and similar phenomenon in the compression process.The compression limit of the lever is about 7 times of the tension limit,and its bearing capacity is much higher than the tension capacity.

Keywords:fused deposition;3D printing;Mechanical properties;PLA levers

3D printing technology,praised as an important symbol of the“Third Industrial Revolution”,is one of the most concerned advanced manufacturing technologies.At present,3D printing technology has been widely used in all aspects of industrial production and people's daily life, such as aerospace, biomedical, automobile industry,education,literary and artistic creation and family entertainment.People's work and life style are changing due to 3D printing technology.

Fused deposition technology is currently the mainstream desktop-level 3D printing technology,which is highly recommended due to its convenient operation and simple principle.However, fused deposition of 3D printed PLA materials has the problem of insufficient intensity[1],which can only be used for viewing and functional verification in most cases.On the intensity of 3D printing components,scholars have carried out more research,for example,Jiang Xin and others studied the mechanical properties of ceramic matrix composites reinforced by 3D printing carbon fiber through compression experiments[2],Wang He studied the photosensitive resin and its mechanical properties reinforced by short carbon fiber through tension,compression and bending experiments.

In this paper,the mechanical properties of 3D printed PLA levers with specific filling rate and filling form are studied by experimental methods.The load-deformation and stress-strain changes of the levers under tension and compression are analyzed,and the tension and compression strength limits of 3D printed levers are obtained.

Ⅰ.Experimental Design

（i）Preparation of 3D Printing Specimens

The tension and compression specimen models are designed in Pro/E 3D modeling software,exported to STL format,then imported into slicing software to slice and set printing model,and finally printed with desktop 3D printer, as shown in Figure 1.

Fig.1 3D Printing Process of Levers

The filling rate of specimens is 15%,and its filling form is square grid.The diameter of the tension specimen is 10mm,and the gauge length is 70mm,80mm and 90mm respectively.The diameter of the compression specimen is 15mm and the length is 25 mm.

（ii）Experimental Process of Tension &Compression

Tension and compression tests were carried out on the above-mentioned specimens using a universal mechanical testing machine.The loading rate of tension test is 1mm/min and the loading ends when the specimen breaks.The loading rate of compression experiment is 2mm/min,and the loading is finished when a large dislocation deformation of time comes.The tension and compression experimental results are shown in figure 2 and 3.

Fig.2 Tension Experiment

Fig.3 Compression Experiment

During the tension experiment,the loading and the elongation of the lever are recorded on the computer in real time,and the diameter of the lever at a specific interval time is measured.In the compression experiment,the load and compression deformation are recorded in real time, and the diameter of the lever is measured in real time with vernier caliper.

Ⅱ.Results and Discussion

（i）Lever Tension

Fig.4 shows the load and deformation variation curve of the 3D printed lever during tension.It can be seen from the figure that,with the increase of deformation,the load shows a stepped increase:after loading for a period of time,the deformation increases without changing the load, and then the load continues to increase with the deformation, thus circulating until the lever breaks.

The same rule also exists in the stress-strain curve,as shown in fig.5.This shows that there is creep phenomenon in the tension process of 3D printed PLA levers,which means the stress (or load)is constant while the strain (or deformation) is variational.From the figure,it is known that creep phenomenon exists in the whole elastic deformation stage.When the stress reaches 3.4MPa,the levers undergo plastic deformation;when the stress reaches 4.5MPa,the levers undergo necking and fracture.

Thereby,it can be judged that when the filling rate is 15%,with the diameter of 10mm,and the effective tension length of 80 and 90mm,the tension elastic limit of the lever is about 3.4MPa,and its tension limit is about 4.5MPa.According toσ=Eε，it is known that its elastic modulus is about 0.152GPa.

（ii）Lever Compression

Fig.6 shows the load deformation curve of the round lever during compression.When the load reaches 2411N, the lever deformation increases rapidly,while the load decreases rapidly first,then decreases slowly,and finally gradually flattens out.It shows that the deformation is mainly elastic deformation when the load is less than 2411N;while the deformation of the lever is plastic deformation when the load exceeds this numeric.

Fig.7 is a stress-strain curve under compression,and the change of the curve is basically consistent with that of the load-deformation curve.When the load is 2411N,the stress value is 30.7MPa,which is the strength limit of the component.However,before the complete plastic deformation occurs,the stress rises slowly for a period of time.During this period of slow rise, both elastic deformation and plastic deformation occur.Therefore,it can be determined that the compression elastic limit should be less than 30.7MPa,about 21.3MPa.

Fig.4 Tension Load-Deformation Curve of Lever

Fig.5 Stress-Strain Curve of Tension Lever

Fig.6 Compression Load-Deformation Curve of Lever

Fig.7 Compression Stress-Strain Curve of Lever

Ⅲ.Conclusion

Taking the filling rate of 15%and the square filling form as an example,this paper studies the tension and compression mechanical properties of 3D printed PLA levers by experimental methods.After analysis and discussion,the following conclusions are drawn:

(1)Creep exists in the tension process of the lever, and it even exists in the whole tension deformation process;

(2)The tension elastic limit of the lever is about 3.4MPa and the stretch limit is about 4.5MPa；

(3)The elastic limit and compression limit of round lever are about 21.3MPa and 30.7MPa respectively.

(4)The compression limit of 3D lever is about 7 times of the tension limit,which indicates that the capacity of 3D lever to bear compression load is much higher than that to bear tension load.