2017 2nd International Conference on Applied Mechanics, Electronics and Mechatronics Engineering (AMEME 2017) ISBN:

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1 2017 2nd International Conerene on Applied Mehanis, Eletronis and Mehatronis Engineering (AMEME 2017 ISB: Investigation on Strain Fatigue Lie o Metal Bar with V-shaped oth in a Radial-orging Cropping Method Li-jun ZHAG 1, *, Xian-eng CHE 1, Sheng-dun ZHAO 2, Zhen-wei WAG 3, Han-xiang WAG 1, Hao JIAG 1, Yan-xin LIU 1 and ai-ming LI 4 1 College o Mehanial and Eletroni Engineering, China Universit o Petroleum, Qingdao, China 2 Shool o Mehanial Engineering, Xi an Jiaotong Universit, Xi an, China 3 Shool o Aeronautis and Astronautis, Universit o Eletroni Siene and Tehnolog o China, Chengdu, China 4 Jiangsu Forged Pipe Fittings Co., LTD, Yanheng, China *Corresponding author Kewords: Metal bar, Radial-orging ropping, Strain atigue lie, V-shaped noth. Abstrat. To estimate the radial-orging ropping time auratel, it is essential to obtain the strain atigue lie (SFL o the metal bar with V-shaped noth. Aording to the radial-orging ropping mehanism, the relation urve between the atigue strain and the SFL is onstruted. Based on it, a new SFL ormula o the metal bar with V-shaped noth, whih is related to the rature dutilit o material, the atigue strain ritial value and the stress onentration ator o the V-shaped noth, is proposed. The omparison results or the metal bars show that the relative errors between the results obtained b the new SFL ormula and the orresponding experimental results are within 10%. Introdution The baiting o metal bars is the irst proess and is widel used in industrial prodution. owadas, the required baiting amount is numerous annuall and is still inreasing ear b ear [1]. However, the urrent ropping proesses are plagued with a big shearing ore, a poor bar ross-setion qualit and a long ropping time. Thereore, a new method with the radial-orging ropping whih is a promising low-stress blanking proess has been proposed [2, 3]. In the ropping proess, the mahine skillull utilizes the radial-orging ation to make the rak propagate along the preabriated V-shaped noth or shearing the bar. It is also a ast and energ-saving ropping sstem beause o the stress onentration eet o the V-shaped noth in the bar [4, 5]. However, the radial-orging ropping results show that the ropping time is long and not stable. Ater repeated analses, it has been onirmed that the rak SFL o the bar with V-shaped noth is not studied learl. Thereore, a new SFL ormula o the bar with V-shaped noth is proposed and the orresponding experiments are also arried out in this paper. The Work Priniple o the Radial-orging Cropping The mehanial part o the radial-orging mahine mainl onsists o ive parts (as shown in Figure 1 and the radial displaement adjustment mehanism (not given in Figure 1 [6]. Beore the mahine works, one end o the bar with V-shaped noth is ixed on the lamping die and the other end is plaed at the enter o the main shat as shown in Figure 2. In the plane perpendiular to the axis o the bar, there are seven stationar eeding rollers and our ropping hammers whih are homogeneousl inlaid in the guide hute o the main shat and an rotate with the main shat snhronousl. In ourse o ropping, the load ated on the bar is distributed uniorml along its irumerene. When the main shat rotates one irle, the bar an be uniorml hit 28 times. As the speed o the main shat is high, up to 3500r/min, the rak at the V-shaped noth tip will propagate uniorml. With the inrease o the displaement load ated on the bar, the rak at the V-shaped noth tip grows stabl until the bar breaks. 97

2 1- Feeding roller; 2-Cropping hammer; 3-Blanking die; 4-Main shat; 5-Metal bar Figure 1. The work priniple o the radial-orging ropping method[6]. Figure 2. The ore diagram o the metal bar. The Strain Fatigue Lie or the Metal Bar with V-shaped oth Establishment o ew Strain Fatigue Lie Formula The initiation time o the V-shaped noth tip rak aounts or about 80% o the ropping time [7], so the SFL o the bar in this paper reers to the rak initiation time. With the data proessing method, the SFL urve o the bar is proposed as shown in Figure 3 based on the radial-orging ropping mehanism. This urve meets two onstraint onditions: irst, the bar will rature in one-wa 1/4-le; seond, the SFL tends to ininit when the atigue strain range ε is less than the ritial value o the atigue strain ε. Figure 3. Strain atigue lie urve o the metal material. Based on the urve in Figure 3 and data proessing results, the expression o the SFL proposed in this paper is given b (, (, C D A ε ε = ε ε ε. (1 Where ε is the material rature dutilit and ε is the ritial value o atigue strain; ε D is the damage strain range, ε D = ε ε ; is the SFL; A( ε, ε is the atigue strain strength and C( ε, ε is the atigue strain index. Both the strain atigue strength and the strain atigue index are untions o ε and ε. Aording to material mehanis, the material rature dutilit is a nominal strain. Under the ation o 1/4-le li load, when the bar ratures, the atigue strain range is denoted as ε = ε

3 Thereore, ater transormation, Eq. (1 an be written as 1 ε ( = 4 2ε 1 C ( ε, ε. (2 Based on Zheng s ormula [8], and negleting the inluene o the rature dutilit, the atigue strain ritial value an be expressed as 2σ 1 ε = ln( + 1. (3 E Where σ 1 is material s ield strength and E is Young s modulus. Ater the omparison o the atigue strain ritial value obtained rom experiments and Eq. (3, the aura o Eq. (3 an be proved extremel high with the biggest relative error o 0.433%. As the ators inluening the strain atigue index are ε and ε, the ollowing expression an be obtained b 1 1 ε log = log( + log( 4 C( ε, ε 2ε. (4 In the double logarithmi oordinates, the relationship between log and log( ε 2ε is linear and the slope k o the straight line is as ollowing k ε log( 2ε 1 = C( ε, ε =. (5 log B means o the least square method, the strain atigue index or dierent materials is alulated b C ε ε 2 ( ε, ε = (log i / (log 4 i (log i i= 1 2ε i = 1 2ε. (6 Based on it, b means o the data itting and the Talor deomposition method based on above slope values, the expression o the strain atigue index is obtained b C ε ε ξ ξ ξ ξ ξ ξ ξ Where ξ = log(2 ε ε (, = + +. (7 Analsis o the Strain Fatigue Lie Formula Aording to Eq. (2, there is the same starting point in the double logarithmi oordinates or the SFL ormula proposed in this paper, i.e., when ε = 2ε, = 1/ 4, whih satisies the onstraint ondition o the SFL. (a (b ( Figure 4. The alulation data and the orresponding experimental data o SFL[3]: (a Fatigue lie urve with 52100; (b Fatigue lie urve with AM350H; ( Fatigue lie urve with 1100Al. 99

4 Figure 4 shows that the strain atigue urves obtained b Eq. (2 are in good agreement with the urves obtained b the existing experimental data in [6], whih indiates that the SFL ormula proposed in this paper is reasonable. Calulation o the ew Strain Fatigue Lie or the Metal Bar with V-shaped oth In the state o three-dimensional stress, the plasti deormation at the V-shaped noth tip is ver small. Thereore, or the bar with V-shaped noth, Eq. (2 is denoted as the ollowing expression 1 ε ( = 4k 2ε φ 1 C ( ε, ε. (8 Where k φ is the stress onentration ator o the V-shaped noth and its expression is [9] s φ ( d d kφ = 1 + (2 ( d / b 1 [1 ( ], (9 s 180 d 3 d 1 d 3 d 5 d 35 d d b 8 b 2 b 8 b 16 b 128 b b = ( ( (1 [1 (1 (1 (1 ( (1 ] Where b is the radius o the bar, as shown in Figure 2; d is the depth o the V-shaped noth; s is the radius at the noth bottom and φ is the lare angle o the V-shaped noth. Experimental Results and Disussion To veri the availabilit o Eq. (8, the radial-orging ropping experiments or bars are arried out. The bar diameter is 15mm, s= mm, d= mm, φ =60º-90º, and other parameters are shown in Table 2. B obtaining the rature dutilit, the ritial value o atigue strain and the stress onentration ator o the V-shaped noth, Table 3 shows that the relative errors between the results o the SFL obtained b Eq. (8 and the orresponding experimental results are within 10%, whih also urther proves that the proposed ormula o the SFL is reasonable. Under dierent ontrol modes, the ross-setions o 45 steel bar and LY8 bars are shown in Figure 5, whih show that the smoothness o the bar ross-setions is high and stable. Table 2. Material parameters. ε 1 Material σ 1 /Mpa ψ k /% E /Pa C( ε, ε ε e Cr e (a (b ( (d (e ( Figure 5. The ross-setions o 45 steel and LY8 bars under dierent ontrol modes: (a 45 steel with step derement urve; (b 45 steel with linear derement urve; ( 45 steel with onvex ar derement urve; (d LY8 with step derement urve; (e LY8 with linear derement urve; ( LY8 with onvex ar derement urve

5 Table 3. Calulation results obtained b Eq. (8 and the orresponding experimental results. Material 45 40Cr ε alulation result/ le experimental result/ le relative error % 4.75% 2.49% 5.13% 2.00% 5.91% 3.89% 2.24% 9.39% 9.31% 1.88% 9.76% Summar Based on the radial-orging ropping mehanism, the relation urve between the atigue strain and the atigue lie is onstruted, whih an satis two onstraint onditions: the material will rature in one-wa 1/4 le and the SFL tends to ininit when the atigue strain range is less than the ritial value o atigue strain. Based on it, a new SFL ormula o the metal bar with V-shaped noth is proposed. The omparison results show that the relative errors between the results obtained b the SFL ormula proposed in this paper and the orresponding experimental results are within 10%, whih proves that the new SFL ormula is reasonable. In addition, the experimental results show that the ross-setion smoothness o ever segment o the bars is ver high and stable. Aknowledgements The author wishes to express gratitude to the ational atural Siene Foundation o PR China (Approval o and the Fundamental Researh Funds or the Central Universities (Approval o. 15CX08007A, whih have supported this work. Reerenes [1] Xuan Liu, Advaned manuaturing tehnolog, Peking Universit Press, Beijing, 2012, pp [2] Yong Tang, Sheng-dun Zhao, Zhen-wei Wang. A novel tpe o preision ropping mahiner using rotar striking ation. Pro. IMehE, Part C: Journal o Mehanial Engineering Siene. 223 ( [3] Zhen-wei Wang, Stud on the new tpe radial-orging atigue ropping method o metal bar and its atigue and rature rules. Dotor's degree thesis o Xi an Jiaotong Universit. China, [4] Li-jun Zhang, Sheng-dun Zhao, Jing Lei, Wei Liu, Investigation on the bar lamping position o a new tpe o preision ropping sstem with variable requen vibration, International Journal o Mahine Tools and Manuature. 47( [5] Chun-jian Hua, Sheng-dun Zhao, Li-jun Zhang, Wei Liu, Investigation o a new-tpe preision ropping sstem with variable-requen vibration, International Journal o Mehanial Sienes. 48 ( [6] Li-jun Zhang, Sheng-dun Zhao, Zhen-wei Wang, Researh on radial motion harateristi o the ropping hammer in radial-orging ropping method, Advanes in Materials Siene and Engineering. (2015, Artile ID , 8 pages, doi: /2015/ [7] Xue-lai. Zhang, Investigation in the mehanism o a low stress preision bar ropping sstem with variant requen vibration method, Master's degree thesis o Xi an Jiaotong Universit. China,

6 [8] Xiu-lin Zheng, Quantitative theor o metal atigue, orthwestern Poltehnial Universit Press, Xi'an, 1994, pp [9] Li-jun Zhang, Jin-heng Zhao, Researh o eets o bar geometri parameters on initial external ore in preision ropping, International Journal o Advaned Manuaturing Tehnolog. 68 (