Experimental and Numerical Evaluation on Deformation and Fracture Mechanism of Cast Duplex Stainless Steel Tubular Specimen

The deformation behavior and fracture mechanism of cast duplex stainless steel tubular specimens under different tensile stages were investigated through experimental and numerical evaluation. The results showed that the axial stress was redistributed due to the necking of the tubular specimen, the axial stress near the internal wall was larger than those near the external wall, and its maximum axial stress was distributed between the internal wall and the center of the wall thickness. Microcracks and voids were initiated under the maximum shear stress along the δ/γ phase interface and propagated to the ferrite interior. The voids were connected and merged into the main crack through the propagation of the microcracks. Moreover, the main crack first propagated to the internal wall and then rapidly propagated to the external wall. The fracture morphology can be divided into three types: shear lip zones that can be found on both the internal and external walls, and shear lip zones that can be found on either only the internal wall or the external wall.

Failure Analysis of Hydraulic Cylinder Bolt on Turntable Vibrating Compactor in Aluminum Processing Plant

The aluminum and its alloy have several characteristics i.e. relatively low density, high electrical and thermal conductivity and also good in corrosion resitance. The molding process of green anode blocks at an aluminum plant is carried out by an anode forming system. In this system, there is a printer called as turntable vibrating compactor or referred to as a ‘shaking machine’. During 55 seconds of anode block compaction, the fluctuating stress would be received by hydraulic cylinder bolt due to vibrations of the turntable vibrating compactor. Fluctuating stress that works continuously on the bolt can increase the tendency of failure. This paper aims to find out the causing factors and alternative solution for failure of the hydraulic cylinder bolt. To determine the cause of failure, several methods are carried out, i.e. fractography investigation, metallography examination according to ASTM E3-95, hardness testing according to ASTM E92-17 and tensile testing according to ASTM E8/E8M-16a. Fractography investigation show the failure mode of low cycle fatigue due to the application of high nominal stress. This is indicated by the presence of ratchet, beach mark, river mark and shear lip. The short life of the bolt due to the hardness and strength of the bolt after undergoing the heat treatment process Q + T cannot increase its endurance limit.

Influence of different filler weld wire chemistries on metallurgical and mechanical behavior of ultrahigh strength steel welded joints

Three different filler combinations comprising of ferritic, austenitic, and (ferritic + austenitic) were used to fabricate butt welded joints on 15 mm thick ultrahigh strength steel using hybrid arc welding processes. Owing to different weld metal compositions, a significant variation in metallurgical properties of these welds was observed, which consequently affected their mechanical properties in terms of tensile and impact toughness. Acicular ferrite with relatively soft zones formed in the ferritic weld metal imparted better impact toughness and ductility, whereas the joints welded using austenitic filler wire due to formation of hard martensitic structure showed high hardness across all their zones which resulted into higher tensile strength but poor ductility and impact toughness. SEM fractographs facilitated studying of shear lip formation and percentage shear area, and could be correlated with the ductility and impact toughness of the welded joints to a reasonable extent. Among all the welds, ferritic filler showed relatively less joint efficiency as well as ultimate tensile strength, but could be considered as a better choice over the austenitic as well their combination (ferritic + austenitic), as it performed better in terms of tensile ductility as well as impact toughness.

Inverse Fracture in DWTT and Brittle Crack Behavior in Large-Scale Brittle Crack Arrest Test

The drop weight tear test (DWTT) has been widely used to evaluate the resistance of linepipe steels against brittle fracture propagation. Although there is an ambiguity in the evaluation of DWTT results if inverse fracture appears on the fracture surfaces, the cause of inverse fracture is not yet fully understood. In the present work, DWTTs were performed with X65, X70, and X80 steel linepipes. In addition to the conventional DWTT specimen with a pressed notch (PN), PN specimens with a back slot (BS) and specimens with a chevron notch (CN) or static precrack (SPC) were also examined, and the fracture appearances in different strengths and different initial notch types were compared. Although the frequency of inverse fracture in these DWTTs was different with each material and each specimen type, there was no material or specimen type that was entirely free from inverse fracture. The purpose of the DWTT is to evaluate the brittle crack arrestability of the material in a pressurized linepipe. Therefore, the DWTT results should be examined with a running brittle crack arrest (BCA) test. A large-scale BCA test with temperature gradient was also performed with the X65 mother plate, and the shear area fraction measured in the DWTT fracture surface was compared with the local shear lip thickness fraction in the BCA test. Based on the results, the count of inverse fracture in the DWTT was discussed in comparison with the long BCA behavior in the BCA test.

Plastic Deformation and Damage Behavior of AL6XN Super-Austenitic Stainless Steels

Tensile and compressive deformation and damage behaviors of Al6XN super-austenitic stainless steels were examined at different strain rates. The deformation and fracture surfaces were characterized by scanning electron microscopy (SEM). It was found that the uniaxial deformation (tensile or compressive) behaviors of Al6XN stainless steel shows a low strain rate sensitivity over the range of 10-4s-1 - 10-2s-1. The tensile and compressive yield strengths measured are nearly comparable. The steel shows a good tensile plasticity. Dislocation slip deformation is the main characteristic of uniaxial deformation. All fracture surfaces induced by tensile deformation at different strain rates can be divided into two parts, i.e., fibrous zone and shear lip zone. The fibrous zone consists of dimples with a bimodal size.

Study on Ductile Fracture Including Shear-Lip Fracture under Mixed Mode Loading Condition

Dimple fracture tests are conducted under mode I and mixed mode lading conditions. Dimple fracture zone and shear-lip fracture zone are observed by scanning electron microscope precisely. It is found that crack growth direction is affected largely by the change of loading condition. It is also found that the differences of fracture pattern between mid-plane and at free surface are very large. Void diameter and crack growth direction are measured. Numerical simulation is conducted to simulate fracture tests in three-dimensional field. Gurson’s constitutive equation is used and large deformation analyses are conducted. It is assumed that void nucleation is controlled by both plastic strain and stress. Numerical results are compared with those of experiments. It is found that results of numerical simulation agree well with those of experiment qualitatively.