title: Analysis of fracture, fatigue, and metallurgical properties of dissimilar TIG & RFW Welds: S355J2/SS316L and Ti-64/Ti-1023

authors: Das, Rajkumar

abstract: Weld joints comprising dissimilar metals with varying compositions are widely utilized across numerous contemporary industrial sectors such as aerospace, automotive manufacturing, shipbuilding, oil and gas, power generation, and medical device production. They offer cost efficiency, performance enhancement, weight reduction, design flexibility, and functionality. However, welding dissimilar metals with varying compositions poses complexity due to compositional gradient and differences in microstructure, leading to variations in properties across the joint. Gaining insight into the influence of parameters in welding on material properties for manufacturing defect-free welded joints is crucial. Nonetheless, there is a considerable gap in knowledge in understanding the relationship between welding parameters, microstructure, fracture toughness, and fatigue in dissimilar material joints.
This study focuses on investigating how parameters in welding influence the microstructure and fracture toughness of welds between two dissimilar materials i.e. structural steel (S355J2) and stainless steel (SS) (316L) using Rotary Friction Welding (RFW) and Tungsten Inert Gas (TIG) welding. Additionally, the study explores how parameters in welding affect the microstructure and fatigue characteristics of welds between two dissimilar titanium alloys i.e. Ti-6Al-4V (Ti-64) and Ti-10V-2Fe-3Al (Ti-1023) using RFW. To achieve the project objectives, dissimilar welding preforms of S355J2 and SS316L are meticulously prepared using corresponding pipe pup pieces and welded via RFW and TIG processes. A comprehensive series of tests are conducted, including microstructural analysis, tensile, hardness, and fracture toughness characteristics are accomplished using compact tension (CT) specimens extracted from various zones of both dissimilar weld joints. For titanium, dissimilar weld joints are fabricated using a round bar of Ti-64 and Ti-1023 via RFW, and tests, including microstructural analysis, tensile, hardness, and stress-controlled high cycle fatigue (HCF), are performed.
Results reveal significant microstructural variations in both dissimilar welding processes for the S355J2 and SS316L as well as the Ti-64 and Ti-1023 alloys. RFW joint between S355J2 and SS316L shows less instability in hardness across the weld with the highest hardness of 208 HV1 in the thermo-mechanically affected zone (TMAZ) of S355J2. Noticeable changes in hardness are observed across the TIG weld with 419 HV1 at the weld centre line (WCL) due to chromium carbide precipitation and 284 HV1 at the TIG heat affected zone (HAZ) of S355J2 is attributed to martensite formation. Both welds exhibit superior tensile characteristics, with the RFW weld displaying ultimate tensile strength (UTS) of 540 MPa and yield strength (YS) of 367 MPa, while the TIG weld shows UTS of 526 MPa and YS of 300 MPa. Tensile failures predominantly occur on the S355J2 side, exhibiting ductile features. Both welds show nearly identical fracture toughness (KQ) values, closely matching those of the parent metal, whereas, in terms of crack tip opening displacement (CTOD), RFW-WCL shows superior performance with 0.35 mm compared to TIG-WCL's 0.32 mm. Notably, the HAZ of S355J2 in the TIG weld exhibits the lowest CTOD of 0.31 mm. Fractography exhibits ductile failure, except for the TIG WCL, which displays cleavage fracture.
In the RFW joint between Ti-64 and Ti-1023, the highest hardness of 342 HV1 occurs at the WCL, gradually diminishing on either side of the weld, attributed to formation of hard microstructural phases and the growth of secondary alpha (αs) phases. The weld exhibits remarkable tensile properties, comparable with those of the parent metal, with a UTS of 826 MPa and an YS of 792 MPa. Tensile failures primarily manifest on the Ti-1023 side, demonstrating ductile characteristics. The HCF test, conducted at a frequency of 40 Hz with a R value of 0.1, reveals a fatigue strength of the weld at 550 MPa, surpassing that of the Ti-64 parent metal. In all HCF specimens, crack initiates at the surface, with those under higher stress exhibiting a narrow crack propagation area characterized by coarse fatigue striation marks indicative of dominant tensile overloading, while specimens under lower stress reveal a wider crack propagation area with quasi-cleavage facets and very fine fatigue striations.
Overall, the study findings establish that the RFW process yields a robust dissimilar weld joint between different materials S355J2 / SS316l and Ti-64 / Ti-1023.

text: Analysis of fracture, fatigue, and metallurgical properties of dissimilar TIG & RFW Welds: S355J2/SS316L and Ti-64/Ti-1023 Weld joints comprising dissimilar metals with varying compositions are widely utilized across numerous contemporary industrial sectors such as aerospace, automotive manufacturing, shipbuilding, oil and gas, power generation, and medical device production. They offer cost efficiency, performance enhancement, weight reduction, design flexibility, and functionality. However, welding dissimilar metals with varying compositions poses complexity due to compositional gradient and differences in microstructure, leading to variations in properties across the joint. Gaining insight into the influence of parameters in welding on material properties for manufacturing defect-free welded joints is crucial. Nonetheless, there is a considerable gap in knowledge in understanding the relationship between welding parameters, microstructure, fracture toughness, and fatigue in dissimilar material joints.
This study focuses on investigating how parameters in welding influence the microstructure and fracture toughness of welds between two dissimilar materials i.e. structural steel (S355J2) and stainless steel (SS) (316L) using Rotary Friction Welding (RFW) and Tungsten Inert Gas (TIG) welding. Additionally, the study explores how parameters in welding affect the microstructure and fatigue characteristics of welds between two dissimilar titanium alloys i.e. Ti-6Al-4V (Ti-64) and Ti-10V-2Fe-3Al (Ti-1023) using RFW. To achieve the project objectives, dissimilar welding preforms of S355J2 and SS316L are meticulously prepared using corresponding pipe pup pieces and welded via RFW and TIG processes. A comprehensive series of tests are conducted, including microstructural analysis, tensile, hardness, and fracture toughness characteristics are accomplished using compact tension (CT) specimens extracted from various zones of both dissimilar weld joints. For titanium, dissimilar weld joints are fabricated using a round bar of Ti-64 and Ti-1023 via RFW, and tests, including microstructural analysis, tensile, hardness, and stress-controlled high cycle fatigue (HCF), are performed.
Results reveal significant microstructural variations in both dissimilar welding processes for the S355J2 and SS316L as well as the Ti-64 and Ti-1023 alloys. RFW joint between S355J2 and SS316L shows less instability in hardness across the weld with the highest hardness of 208 HV1 in the thermo-mechanically affected zone (TMAZ) of S355J2. Noticeable changes in hardness are observed across the TIG weld with 419 HV1 at the weld centre line (WCL) due to chromium carbide precipitation and 284 HV1 at the TIG heat affected zone (HAZ) of S355J2 is attributed to martensite formation. Both welds exhibit superior tensile characteristics, with the RFW weld displaying ultimate tensile strength (UTS) of 540 MPa and yield strength (YS) of 367 MPa, while the TIG weld shows UTS of 526 MPa and YS of 300 MPa. Tensile failures predominantly occur on the S355J2 side, exhibiting ductile features. Both welds show nearly identical fracture toughness (KQ) values, closely matching those of the parent metal, whereas, in terms of crack tip opening displacement (CTOD), RFW-WCL shows superior performance with 0.35 mm compared to TIG-WCL's 0.32 mm. Notably, the HAZ of S355J2 in the TIG weld exhibits the lowest CTOD of 0.31 mm. Fractography exhibits ductile failure, except for the TIG WCL, which displays cleavage fracture.
In the RFW joint between Ti-64 and Ti-1023, the highest hardness of 342 HV1 occurs at the WCL, gradually diminishing on either side of the weld, attributed to formation of hard microstructural phases and the growth of secondary alpha (αs) phases. The weld exhibits remarkable tensile properties, comparable with those of the parent metal, with a UTS of 826 MPa and an YS of 792 MPa. Tensile failures primarily manifest on the Ti-1023 side, demonstrating ductile characteristics. The HCF test, conducted at a frequency of 40 Hz with a R value of 0.1, reveals a fatigue strength of the weld at 550 MPa, surpassing that of the Ti-64 parent metal. In all HCF specimens, crack initiates at the surface, with those under higher stress exhibiting a narrow crack propagation area characterized by coarse fatigue striation marks indicative of dominant tensile overloading, while specimens under lower stress reveal a wider crack propagation area with quasi-cleavage facets and very fine fatigue striations.
Overall, the study findings establish that the RFW process yields a robust dissimilar weld joint between different materials S355J2 / SS316l and Ti-64 / Ti-1023.

year: 2024-05-23

title: Non-suicidal self-injury: Suicide risk or social activity?

authors: Curtis, Cate

subjects: NSSI

abstract: Deliberate self-harm (DSH) has been conceptualised as indicative of mental illness, on a continuum ending with suicide. Recently our understanding of DSH has become more nuanced, with distinctions made between suicidal behaviour and non-suicidal self-injury (NSSI). Indeed, there is some evidence that NSSI may be consciously countersuicidal. Moreover, NSSI appears to have recently increased markedly among young women. This research explores the motivations, meanings and functions of NSSI in young New Zealand women through 19 in-depth interviews. The results show that precursors range from serious anguish including suicidality, to purely social, with functions from the alleviation of distress to participation in a social activity. Often minimal physical or psychological harm is involved, either preceding NSSI, or as a result. Previous beliefs about the dynamics and the social contexts in which NSSI occurs are thus problematic, as are assumptions about the appropriate support. Though a potential indicator of mental ill-health, NSSI may be a harm-reduction technique, or a relatively normalised teenage activity within the peer group.

text: Non-suicidal self-injury: Suicide risk or social activity? Deliberate self-harm (DSH) has been conceptualised as indicative of mental illness, on a continuum ending with suicide. Recently our understanding of DSH has become more nuanced, with distinctions made between suicidal behaviour and non-suicidal self-injury (NSSI). Indeed, there is some evidence that NSSI may be consciously countersuicidal. Moreover, NSSI appears to have recently increased markedly among young women. This research explores the motivations, meanings and functions of NSSI in young New Zealand women through 19 in-depth interviews. The results show that precursors range from serious anguish including suicidality, to purely social, with functions from the alleviation of distress to participation in a social activity. Often minimal physical or psychological harm is involved, either preceding NSSI, or as a result. Previous beliefs about the dynamics and the social contexts in which NSSI occurs are thus problematic, as are assumptions about the appropriate support. Though a potential indicator of mental ill-health, NSSI may be a harm-reduction technique, or a relatively normalised teenage activity within the peer group.

year: 2017

title: What is Māori typography?

authors: Kennedy, Nikki Eileen

subjects: Māori Design

abstract: Te Reo Māori was traditionally an oral language similar to many indigenous cultures. Writing systems were not familiar to Māori until 1769 where Māori were introduced to the written language by Pākehā. Early Māori writing can be found printed, carved and painted in a number of different parts of Māori society. These myriad texts were strongly influenced and inspired by Pākehā biblical texts and newspapers. The influence of Pākehā texts meant that overtime the written language of Te Reo Māori had a Pākehā visual identity.

To date, there is minimal research about the history and visual identity of Māori typography. The lack of research and resources about Māori typography confirms how underdeveloped Māori typography is and highlights the potential for research and development in this space.

This thesis aims to explore Māori typography. In particular, this thesis will provide an understanding of how Māori typography has evolved, addressing the perceptions of Māori text features and advice on design guidance of Māori typography.

Two studies within this thesis involved analysing the text-based features in 21 Māori newspapers dated from 1842-1935. Māori newspapers are a valuable resource that captured moments in history and also early displays of Māori text. The second study involved interviews with 50 participants — Māori and non-Māori, from a range of different backgrounds — who provided their understandings and perceptions surrounding the features of Māori text.

The results from these studies have shown that the serif typeface classification was commonly used in early print such as Māori newspapers. Serif lettering also reminded participants in our studies of early Māori texts such as old text books and newspapers. This appears to be the reason as to why, a strong theme of serifs and the style of Didone typefaces have been used throughout Māori typography and by default are recognised features of Māori typefaces today.

Having analysed Māori newspapers, an unexpected finding appeared in the 1908 Te Pipiwharauroa newspaper. Two unique letter characters were found that was revolution for Te Reo Māori text of the time. This oddity combined the ‘ng’ letters into one letter character and the ‘wh’ letters into one letter character also. The aim in combining the two letters together was to emphasise the one sound that the ‘ng’ and the ‘wh’ make to avoid confusion in the pronunciation of Māori words. The results showed that these two letter characters appeared from 1908 through to 1912. There is no evidence of these characters appearing after 1912 and also appearing in other newspapers. The two characters were a rare appearance of its time.

As a result of this research it is clear that the visual identity of Te Reo Māori remains unclear and was highly influenced by serif lettering. This thesis highlights the need for more research about Māori typography and design guidance for developing appropriate Māori typefaces that are influenced and inspired by Maori culture.

text: What is Māori typography? Te Reo Māori was traditionally an oral language similar to many indigenous cultures. Writing systems were not familiar to Māori until 1769 where Māori were introduced to the written language by Pākehā. Early Māori writing can be found printed, carved and painted in a number of different parts of Māori society. These myriad texts were strongly influenced and inspired by Pākehā biblical texts and newspapers. The influence of Pākehā texts meant that overtime the written language of Te Reo Māori had a Pākehā visual identity.

To date, there is minimal research about the history and visual identity of Māori typography. The lack of research and resources about Māori typography confirms how underdeveloped Māori typography is and highlights the potential for research and development in this space.

This thesis aims to explore Māori typography. In particular, this thesis will provide an understanding of how Māori typography has evolved, addressing the perceptions of Māori text features and advice on design guidance of Māori typography.

Two studies within this thesis involved analysing the text-based features in 21 Māori newspapers dated from 1842-1935. Māori newspapers are a valuable resource that captured moments in history and also early displays of Māori text. The second study involved interviews with 50 participants — Māori and non-Māori, from a range of different backgrounds — who provided their understandings and perceptions surrounding the features of Māori text.

The results from these studies have shown that the serif typeface classification was commonly used in early print such as Māori newspapers. Serif lettering also reminded participants in our studies of early Māori texts such as old text books and newspapers. This appears to be the reason as to why, a strong theme of serifs and the style of Didone typefaces have been used throughout Māori typography and by default are recognised features of Māori typefaces today.

Having analysed Māori newspapers, an unexpected finding appeared in the 1908 Te Pipiwharauroa newspaper. Two unique letter characters were found that was revolution for Te Reo Māori text of the time. This oddity combined the ‘ng’ letters into one letter character and the ‘wh’ letters into one letter character also. The aim in combining the two letters together was to emphasise the one sound that the ‘ng’ and the ‘wh’ make to avoid confusion in the pronunciation of Māori words. The results showed that these two letter characters appeared from 1908 through to 1912. There is no evidence of these characters appearing after 1912 and also appearing in other newspapers. The two characters were a rare appearance of its time.

As a result of this research it is clear that the visual identity of Te Reo Māori remains unclear and was highly influenced by serif lettering. This thesis highlights the need for more research about Māori typography and design guidance for developing appropriate Māori typefaces that are influenced and inspired by Maori culture.

year: 2020