Tube spinning, also known as flow forming, is one of spinning processes widely used to produce cylindrical components with thin-walled section and high precision [
1,
2]. In this process, the metal is displaced axially along a mandrel, while a continuous and localized plastic deformation is applied by the feeding movement of one or more rollers and rotational motion of the mandrel to reduce the thickness of components [
3,
4]. According to the relationship between the direction of material flow and roller traversing, the process can be classified as forward and backward tube spinning, as shown in
Figure 1 [
5]. 3A21 aluminum alloy is one of the most commonly used alloys for aviation, aerospace and automotive industries because of its versatile properties, economical benefit and no need for-heat-treatment advantages [
6]. However, due to the highly non-linear feature and complicated stress state during tube spinning, it is prone to cracking in 3A21 aluminum spun parts, which severely restricts the improvement of the forming quality and forming limit of components. Therefore, it is necessary to study the damage evolution of 3A21 aluminum alloy to guide the actual production of spun components.
Researches on the damage evolution in spinning process coupled with ductile fracture criteria have been reported in recent years. Ma
et al. [
7] investigated the damage evolution in tube spinnability of TA2 titanium tube with nine types of un-coupled ductile fracture criteria in detail. Their result indicated that except for the Freudenthal, Rice and Tracey (R-T) and Ayada models, all the other models can correctly predict the damage distribution on TA2 titanium tube in spinnability test. Cockcroft-Latham (C-L) criterion provided the highest prediction accuracy on the spinnability of TA2 titanium tube, which was only 9% less than the measured experimental value. Zhan
et al. [
8] predicted the failure occurring in shear spin-forming, splitting spin-forming of LF2M aluminum alloy by embedding the Lemaitre and Cockcroft-Latham (C&L) criteria into the finite element (FE) model. The results showed that the Lemaitre criterion was better than the C&L criterion at accurately predicting the position at which damage will occur. A thermal damage model for tube spinning process of Ti-6Al-2Zr-1Mo-1V combining the Oyane ductile fracture criterion with the relationship among damage threshold, temperature and strain rate was also established by Zhan
et al. [
9]. Their results indicated that the inner surface of the spinning region was the zone most prone to damage due to positive stress triaxiality and large strain rate.
Recently, studies on expansion and accumulation of cavities in ductile material have been carried out. It is often believed that, the ductile failure process of metal material consists of three stages in mesoscopic scale: micro-voids nucleation, growth and coalescence, respectively [
10,
11]. The typical model to describe these three stages is the Gurson-Tvergaard-Needleman (GTN) damage model, which is proposed by Gurson [
10] and further modified by Tvergaard and Needleman [
11]. Compared with other ductile fracture criteria, GTN damage model is a coupled ductile fracture criterion, incorporating the void evolution into the constitutive equations. Generally, GTN damage model and modified GTN damage model are applied to predict void initiation, propagation, and final rupture [
12,
13] combined with FE simulation in some process. Chen and Dong [
12] predicted the damage in deep drawing test of AA6111 aluminum alloy well with a modified GTN yield criterion based on a quadratic anisotropic yield criterion and an isotropic hardening rule. Butcher
et al. [
13] predicted the burst pressure, formability and failure location in tube hydroforming of dual phase (DP600) steel using GTN constitutive model and interpreted the influence of void shape and shear on coalescence. Sun
et al. [
14] analyzed the ductile damage and failure behavior of steel sheet with edge defects under multi-pass cold rolling based on the shear GTN damage model proposed by Nahshon and Hutchinson [
15]. Li
et al. [
16] indicated that the GTN damage model can predict the damage in tube bending process. However, it cannot predict the damage evolution due to the negative stress triaxiality in split spinning. It can be found that most of these studies about GTN damage model concentrate on the simple stress state. Researches on GTN damage model applied in other complicated deformation, such as tube spinning process, are limited. In tube spinning process, many researches on damage evolution have been studied based on other ductile fracture criteria. However, there are few researches on damage evolution based on GTN damage model in this process. Thus, the applicability and limitation of GTN damage model in tube spinning should be evaluated in detailed.
To investigate the applicability of GTN damage model to predict fracture in tube spinning process, an FE model coupled with GTN damage model for forward tube spinning of 3A21-O aluminum alloy is established based on ABAQUS/Explicit platform. Then the applicability of GTN damage model in spinning process is evaluated by experiment. Distributions of the stress triaxiality, the maximum principal stress, and the void volume fraction (VVF) are analyzed to reveal damage evolution in forward tube spinning finally.