A semi-analytical method to evaluate the J-R curve for the surface-cracked round bar under three-point bending

The current paper presents a semi-analytical method for obtaining J-R curves of round bars with elliptical cracks. This method derives the semi-analytical expressions between load and displacement, J-integral and displacement for surface-cracked round bars, based on the energy density equivalence principle, taking into account the effect of material and crack size. The validity of semi-analytical expressions examined by three-dimensional finite element analysis shows that load~displacement curves and J-integral~load curves predicted by the expressions match well with the simulation results. Through fracture toughness testing conducted on the carbon steel 45, the load~displacement data are used to calculate the average J-R curves for the surface-cracked round bar by the semi-analytical expressions. With the distributions of J-integral along the crack front obtained from three-dimensional finite element analyses, this study also determines the J-R curves at different crack-front points.

The Atmospheric Corrosion of Structural Steel after Exposure in the Palm Oil Mill Industry Area of Aceh-Indonesia

The major cause of early failure in the infrastructures of the palm oil industry in Aceh, Indonesia has been discovered to be the corrosion caused by air pollution from exhaust fumes of the factory plants. Therefore, this research was conducted to analyze the effect of the atmospheric corrosion of the structural steel used in the palm oil mill industry. The five types of structural steel used as samples include strip, l-shape, round bar, plate, and SAPH 610 low carbon steel with a carbon content of 0.18%. These specimens were cleansed from dirt, scaled, and rubbed with sandpaper to achieve a grid of 600, later washed with fresh water and rinsed with alcohol, and subsequently exposed to the environment in PT ASN and PT AKTS palm oil mills for 12 months. Moreover, they were placed on a measuring tray for exposure and the corrosion rate was recorded once a month using the mass loss method in line with the ASTM G50. The results showed the steel construction with a round bar shape was more resistant to atmospheric corrosion and the remaining samples were also observed to be safe and relatively resistant based on their classification as being outstanding (< 1 mpy).

Comparison of Modified Mohr–Coulomb Model and Bai–Wierzbicki Model for Constructing 3D Ductile Fracture Envelope of AA6063

Ductile fracture of metal often occurs in the plastic forming process of parts. The establishment of ductile fracture criterion can effectively guide the selection of process parameters and avoid ductile fracture of parts during machining. The 3D ductile fracture envelope of AA6063-T6 was developed to predict and prevent its fracture. Smooth round bar tension tests were performed to characterize the flow stress, and a series of experiments were conducted to characterize the ductile fracture firstly, such as notched round bar tension tests, compression tests and torsion tests. These tests cover a wide range of stress triaxiality (ST) and Lode parameter (LP) to calibrate the ductile fracture criterion. Plasticity modeling was performed, and the predicted results were compared with corresponding experimental data to verify the plasticity model after these experiments. Then the relationship between ductile fracture strain and ST with LP was constructed using the modified Mohr–Coulomb (MMC) model and Bai-Wierzbicki (BW) model to develop the 3D ductile fracture envelope. Finally, two ductile damage models were proposed based on the 3D fracture envelope of AA6063. Through the comparison of the two models, it was found that BW model had better fitting effect, and the sum of squares of residual error of BW model was 0.9901. The two models had relatively large errors in predicting the fracture strain of SRB tensile test and torsion test, but both of the predicting error of both two models were within the acceptable range of 15%. In the process of finite element simulation, the evolution process of ductile fracture can be well simulated by the two models. However, BW model can predict the location of fracture more accurately than MMC model.

Comparison of modified Mohr–Coulomb model and Bai–Wierzbicki model for constructing 3D ductile fracture envelope of AA6063

Ductile fracture of metal often occurs in the plastic forming process of parts. The establishment of ductile fracture criterion can effectively guide the selection of process parameters and avoid ductile fracture of parts during machining. The 3D ductile fracture envelope of AA6063-T6 were developed to predict and prevent its fracture. Smooth round bar tension tests were performed to characterize the flow stress, and a series of experiments were conducted to characterize the ductile fracture firstly, such as notched round bar tension tests, compression tests and torsion tests. These tests cover a wide range of stress triaxiality (ST) and Lode parameter (LP) to calibrate the ductile fracture criterion. Plasticity modeling was performed, and the predicted results were compared with corresponding experimental data to verify the plasticity model after these experiments. Then the relationship between ductile fracture strain and ST with LP was constructed using the modified Mohr–Coulomb (MMC) model and Bai-Wierzbicki (BW) model to develop the 3D ductile fracture envelope. Finally, two ductile damage models were proposed based on the 3D fracture envelope of AA6063. Through the comparison of the two models, it was found that BW model had better fitting effect, and the sum of squares of residual error of BW model was 0.9901. The two models had relatively large errors in predicting the fracture strain of SRB tensile test and torsion test, but both of the predicting error of both two models were within the acceptable range of 15%. In the process of finite element simulation, the evolution process of ductile fracture can be well simulated by the two models. However, BW model can predict the location of fracture more accurately than MMC model.

Protection of objects from local damage and destruction

The paper deals with the dynamic process of local destruction of an object of armor protection. It is modeled as an object of destruction in the form of a spherical shell, and the threat is represented in the form of a metal round bar. Formulas are given and an estimate of the acceleration rate at which the object of armor protection is guaranteed to lose continuity is made. It is shown that if the rod has a tip covered with a layer of iridium, then under certain conditions, due to the fact that this metal has a high dynamic viscosity under intense loads, the object of armor protection is highly likely to be hit.

The study for constant force characteristic of C-shaped superelastic SMA

Clamping devices with constant force or pressure are desired in medical device, such as hemostatic forceps and the artificial sphincter, to prevent soft tissues from injures due to overloading. It is easily obtained by stretching an SMA wire. However, studies with SMA bending round bar have seldom been reported before. This paper studied constant force characteristic of C-shaped round bar with shape memory alloys. Optimization designs of the components were carried out with computational simulation. Numerical results show that the phenomenon of constant force strongly depends on contour curve shape and geometric dimensions of the C-shaped round bar of SMA component.