scholarly journals The fracture toughness of martensite islands in dual-phase DP800 steel

2021 ◽  
Author(s):  
Chunhua Tian ◽  
Christoph Kirchlechner
Keyword(s):  
Fracture Toughness ◽  
Fracture Initiation ◽  
Initiation Toughness ◽  
Dual Phase ◽  
Dp Steel ◽  
Bending Tests ◽  
Damage Initiation ◽  
Linear Elastic ◽  
Steel Grades

Abstract In situ microcantilever bending tests were performed on martensite islands in a dual-phase (DP) steel to extract the fracture toughness of martensite at the microscale and to understand damage initiation during forming of DP steels. All microcantilevers were produced through FIB milling. The martensite islands do not exhibit linear elastic brittle fracture; instead, significant ductile tearing is observed. The conditional fracture initiation toughness extracted by definition and by Pippan’s transfer criterion is Ki = 6.5 ± 0.4 MPa m1/2 and Ki,2% = 10.1 ± 0.3 MPa m1/2, respectively. The obtained value is well-represented by the strength-toughness trend of other ferritic steel grades. Considering the yield stress of the same martensite island, we found that crack initiation can occur only in very large martensite islands or in a banded or agglomerated martensite structure. Graphic abstract

Testing Techniques for Establishing Fracture Resistance of Steel in a Sour Environment

2017 ◽  
Author(s):  
Muhammad S. Ali
Keyword(s):  
Fracture Toughness ◽  
Fracture Resistance ◽  
Crack Extension ◽  
Pipeline Steel ◽  
Fracture Initiation ◽  
Load Level ◽  
Manganese Steel ◽  
Initiation Toughness ◽  
Loading Rates ◽  
Rate Of Increase

It is well established that sour operating environments can give rise to significantly reduced fracture toughness of pipelines made of carbon manganese steel. Fracture resistance of a material is usually defined in terms of a fracture resistance curve, commonly known as an R-curve which is determined by testing pre-cracked specimens under a rising load. Fracture resistance data can be derived by the single specimen method, where crack extension is determined using unloading compliance or the multiple specimen method, where crack extension is measured from the fracture face of each specimen and each specimen is taken to a different load level. The fracture resistance behaviour of API 5L X65 grade pipeline steel determined by testing single edge notched bend specimens in a specific sour environment using both single and multiple specimen test methods is reported. The fracture resistance of the steel was found to be highly sensitive to the loading rates (described by the initial rate of increase of stress intensity factor in the elastic range) applied during the fracture resistance tests. It was possible to identify a loading rate slow enough to provide fracture initiation toughness reasonably close to the expected lower bound toughness. It is possible to produce similar R-curves from single and multiple specimen testing methods (if conditions are otherwise the same). Under comparable loading rates and environmental conditions, side grooved specimens resulted in lower fracture toughness as compared to the toughness determined from the plane sided specimens. It was also noticed that there was a weaker correlation between side grooving and toughness at slower loading rates.

Failure Initiation in Dual-Phase Steel

2013 ◽  
Vol 586 ◽  
pp. 67-71 ◽  
Author(s):  
Ali Ramazani ◽  
Alexander Schwedt ◽  
Anke Aretz ◽  
Ulrich Prahl
Keyword(s):  
Research Work ◽  
Tensile Tests ◽  
Bending Test ◽  
Dual Phase ◽  
Extended Finite Element ◽  
Dp Steel ◽  
Failure Initiation ◽  
Before And After ◽  
Macroscopic Failure

This research work aims to model the failure initiation in dual-phase (DP) steel. A microstructure based approach by means of representative volume elements (RVE) is employed to evaluate the microstructure deformation and the failure initiation on the mesoscale. In order to determine cohesive parameters for martensite cracking, a two level approach has been performed experimentally. First, in-situ bending test in SEM with EBSD measurements before and after the test showed that the crack initiation occurs in martensite islands. Then, mini tensile tests with DIC technique were carried out to identify macroscopic failure initiation strain values. RVE modeling combined with extended finite element method (XFEM) was utilized to model martensite cracking on mesoscale. The identified parameters were validated by comparing the predictions with the experimental results.

Effects of the microstructure and minor elements on the fracture toughness of Nb-Si alloy

2012 ◽  
Vol 1516 ◽  
pp. 163-167
Author(s):  
Takuya Okawa ◽  
Seiji Miura ◽  
Tetsuo Mohri
Keyword(s):  
Fracture Toughness ◽  
In Situ Observation ◽  
Bending Tests ◽  
Minor Elements ◽  
Notched Specimens ◽  
Four Point Bending ◽  
Arc Melting ◽  
High Temperature Structural Material ◽  
Laser Confocal Microscope

ABSTRACTThe development of a new high temperature structural material is recently required in various fields. As one of the potential materials, Nb-Si alloys have attracted attention due to their high melting point and low density. A microstructure composed of ductile Nb matrix containing finely dispersed spherical Nb5Si3 phase is obtained by the addition of ternary elements such as Au and it is found that such microstructure is effective in improving room temperature toughness. The main purpose of the present study is evaluating fracture toughness of Nb-Si-Au alloys using small specimens and investigating the effects of the microstructure and other minor elements on the fracture toughness. Alloy ingots of Nb-15at.%Si-3at.%Au and Nb-3at.%Au are prepared by arc-melting under Ar atmosphere, followed by heat-treatments at up to 1500oC for 100 hours. Chevron notched specimens with a size of 1.0x2.0x10mm are subjected to four-point bending tests under a laser confocal microscope for in-situ observation of crack propagation, and the effect of the microstructure and minor elements such as oxygen on the evaluated fracture toughness is investigated on both the Nb/Nb5Si3 alloys and the Nb solid solution (Nbss) alloys.

scholarly journals Study of Testing Method for Dynamic Initiation Toughness of Sandstone under Blasting Loading

2018 ◽  
Vol 2018 ◽  
pp. 1-13 ◽  
Author(s):  
Dingjun Xiao ◽  
Zheming Zhu ◽  
Rong Hu ◽  
Lin Lang
Keyword(s):  
Fracture Toughness ◽  
Blast Hole ◽  
Fracture Initiation ◽  
Strain Gauges ◽  
Inversion Method ◽  
Numerical Inversion ◽  
Initiation Toughness ◽  
Type I ◽  
Initiation Fracture Toughness ◽  
Sandstone Specimen

In this paper, an internal central single-cracked disk (ICSCD) specimen was proposed for the study of dynamic fracture initiation toughness of sandstone under blasting loading. The ICSCD specimen had a diameter of 400 mm sandstone disc with a 60 mm long crack. Blasting tests were conducted by using the ICSCD specimens. The blasting strain-time curve was obtained from the radial strain gauges placed around the blast hole. The fracture initiation time was determined by circumferential strain gauges placed around the crack tip. The stress history on the blast hole of the sandstone specimen was then derived from measured strain curve through the Laplace transform. The numerical solutions were further obtained by the numerical inversion method. A numerical model was established using the finite element software ANSYS. The type I dynamic stress intensity factor curves of sandstone under blasting loading were derived by the mutual interaction integration method. The results showed that (1) the ICSCD specimen can be used to measure dynamic initiation fracture toughness of rocks; (2) the stress on the blast hole wall can be obtained by the Laplace numerical inversion method; (3) the dynamic initiation fracture toughness of the ICSCD sandstone specimen can be calculated by the experimental-numerical method with a maximum error of only 7%.

scholarly journals Effect of the gold remodeling preparation method on the microstructure and mechanical behavior of steel

2020 ◽  
Vol 2 (10) ◽  
Author(s):  
Christian Oen Paulsen ◽  
Tore Børvik ◽  
Ida Westermann
Keyword(s):  
Elevated Temperatures ◽  
Preparation Method ◽  
Tensile Behavior ◽  
Image Correlation ◽  
Polished Surface ◽  
Dual Phase ◽  
Sem Images ◽  
Dp Steel ◽  
Successful Technique

Abstract The application of gold speckles on a polished surface is a successful technique for improving digital image correlation (DIC) contrast in scanning electron microscope (SEM) images. In the process of creating the gold speckles, the material is subjected to elevated temperatures for prolonged times. As a consequence, not all materials are suitable for the gold speckled method to improve the contrast for DIC measurements during an in-situ SEM tensile test. In this letter, the effect of gold remodeling on two different steels is investigated. These steels are a dual-phase (DP) steel and a ferrite–pearlite steel (NVE36). The results demonstrate that the temperature these steels are subjected to during gold remodeling will influence the tensile behavior of the DP steel while the NVE36 steel is unaffected by the heat treatment. As a result, we can conclude that the gold remodeling method for creating contrast in SEM images may affect the microstructure. However, the effect of these changes depends on the material at hand and will vary from material to material.

Hydrogen Embrittlement Susceptibility of Clad Steel Pipes

2017 ◽  
Author(s):  
Lise Jemblie ◽  
Vigdis Olden ◽  
Bård Nyhus ◽  
Odd Magne Akselsen
Keyword(s):  
Hydrogen Embrittlement ◽  
Base Material ◽  
Fracture Initiation ◽  
Experimental Investigations ◽  
Initiation Toughness ◽  
Steel Pipes ◽  
Ni Interlayer ◽  
Clad Steel ◽  
Hot Rolled

The objective of the present work has been to evaluate the hydrogen embrittlement susceptibility of 316L - X60/X65 carbon steel hot rolled bonded clad pipes through experimental investigations and cohesive zone numerical simulations. Fracture mechanical testing in air and under in situ electrochemical hydrogen charging revealed little hydrogen influence on the samples with a Ni-interlayer between the clad and the base material, while significant hydrogen influence on the sample without a Ni-interlayer. Cohseive zone simulations were able to predict the detrimental influence of hydrogen on the fracture initiation toughness. The simulations suggest that hydrogen trapped at dislocations are mainly responsible for the embrittlement of the clad pipe base material.

The Formation of Multiphase Microstructures in Low-Alloy Steel

2010 ◽  
Vol 638-642 ◽  
pp. 3520-3530 ◽  
Author(s):  
Jilt Sietsma
Keyword(s):  
Mechanical Properties ◽  
Alloy Steel ◽  
Dual Phase ◽  
Low Alloy Steel ◽  
Microstructure Formation ◽  
Basic Principles ◽  
Dp Steel ◽  
Transformation Induced Plasticity ◽  
Steel Grades ◽  
Multiphase Steel

Although relatively simple in its chemical composition, low-alloy steel can form in a wide variety of microstructures, which directly implies that the (mechanical) properties of the material can vary strongly. Mankind has been using this to his advantage for ages, but the requirements for modern production and use of the material necessitate an ever better insight in the formation of these microstructures. Newly developed steel grades like DP-steel (Dual-Phase) or TRIP-steel (Transformation-Induced Plasticity) consist of several of the well-known phases ferrite, bainite, martensite, austenite, which need to be carefully balanced in their amount, composition and morphology to attain the desired material properties. An overview is given of the basic principles of microstructure formation in low-alloy steel, and the implications for several types of multiphase steel microstructures, in relation to the mechanical properties, are discussed.

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