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1. The Effect of Temperature on the Strain-Induced Austenite to Martensite Transformation in SS 316L During Uniaxial Tension

   https://doi.org/10.1007/978-3-030-75381-8_155  

   Mamros E.M., Bram Kuijer (July 2021, Forming the Future. The Minerals, Metals & Materials Series)

   Daehn G., Cao J. (Ed.)

   Controlling the microstructure of components is of interest to achieve optimal final part properties, i.e., materials by design. The manufacturing process itself can affect a material’s characteristics by changing the microstructure. For example, past research has shown that austenite to martensite phase transformation in stainless steel occurs during deformation. Temperature is known to have a significant influence on this phenomenon. In this paper, the effect of temperature on the austenitic to martensite phase transformation in SS 316L under uniaxial tension is investigated. Both a cooling system and a heat exchanger were employed in a uniaxial tension experimental setup to control the temperature. Tensile specimens were strained to fracture at four temperatures of −15, 0, 10, and 20 °C. Digital imaging correlation (DIC) and a thermal imaging camera were used for tests at 0 °C and above to capture strain and temperature data, respectively. Strain and temperature data could not be obtained at −15 °C due to the DIC paint flaking during testing. X-ray diffraction was used to measure the volume fraction of martensite in both the as-received and the tensile-tested materials. 

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2. Martensitic transformation of SS304 truncated square pyramid manufactured by single point incremental forming

   https://doi.org/10.1016/j.cirpj.2024.08.006  

   Mamros, Elizabeth M; Maaß, Fabian; Tekkaya, A Erman; Kinsey, Brad L; Ha, Jinjin (December 2024, CIRP Journal of Manufacturing Science and Technology)

   To investigate the microstructural changes that occur in stainless steel (SS) 304 during single point incremental forming (SPIF), experiments and finite element (FE) simulations were conducted for a truncated square pyramid geometry. Results from material characterization experiments for four stress states, i.e., uniaxial tension, equibiaxial tension, shear, and uniaxial compression, were combined to construct a material model based on the constituent phases and transformation kinetics. The material model was implemented into numerical analyses, where a two-step FE approach was utilized to predict martensite transformation in SPIF with increased computational efficiency. Validation experiments showed good agreement with the martensite transformation predictions from the FE simulations. The four locations along the pyramid wall revealed varying martensite volume fractions because of the differing stress states of bending, stretching, and shear that the blank is subjected to during SPIF, which can affect the microstructure. The stress state can be defined in terms of the stress triaxiality and Lode angle parameter. The FE results indicate that stress triaxiality impacted the martensitic transformation kinetics in SS304 more than the Lode angle parameter for SPIF for this particular material and geometry. Thus, distinct stress states in incremental forming can affect the martensitic transformation locally and, when used strategically, achieve functionally graded materials. This is pertinent to industrial applications requiring custom components, e.g., trauma fixation hardware for medical applications. 

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3. Manipulating martensite transformation of SS304L during double-sided incremental forming by varying temperature and deformation path

   https://doi.org/10.1016/j.cirp.2023.04.015  

   Darzi, Shayan; Adams, Matt D.; Roth, John T.; Kinsey, Brad L.; Ha, Jinjin (January 2023, CIRP Annals)

   Double-sided incremental forming (DSIF) is a die-less sheet metal forming process capable of fabricating complex parts. The flexibility of DSIF can be used for in-situ mechanical properties alteration, e.g., by controlling deformation-induced martensite transformation of austenitic stainless steels. In this paper, SS304L is deformed using DSIF at three different cooling conditions and two different tool paths to affect the martensite transformation. Additionally, finite element analyses were used to understandthe effect of tool paths on springback and plastic strain. Implementing a reforming tool path at the lowest achievable temperature resulted in a martensite volume fraction as high as 95%. 

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4. Experimental Implementation of SS 316L Cruciform Testing to Achieve Various Deformation Paths

   https://doi.org/10.1007/978-3-030-75381-8_166  

   Mamros E.M., Mayer S.M. (July 2021, Forming the Future. The Minerals, Metals & Materials Series)

   Daehn G., Cao J. (Ed.)

   By following varying deformation paths, e.g., a linear path to equibiaxial loading versus a bilinear path of uniaxial loading followed by biaxial loading, the same final strain state can be achieved. However, the stress state that the material is subjected to is considerably different due to the varying deformation. This is of interest in a growing field of stress superposition to improve formability and manipulate final part properties in metal forming applications. One potential application is forming patient-specific, trauma fixation hardware with differing strength and weight reduction requirements in various regions. In this paper, experiments were performed on a custom fabricated cruciform machine with the goal of subjecting stainless steel 316L to various deformation paths. A novel cruciform specimen geometry was designed in collaboration with the US National Institute of Standards and Technology to achieve large strain values in the gauge region. Digital Image Correlation was utilized to measure surface strain fields in real time. 

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5. Full-field investigation of in-phase and out-of-phase thermomechanical loading paths in high-temperature shape memory alloys

   https://doi.org/10.1016/j.jallcom.2025.183335  

   Cassagne, Adrien R; Mark, Joshua; Vedula, Ram; Benafan, Othmane; Lagoudas, Dimitris C; Graverend, Jean-Briac le (September 2025, Journal of Alloys and Compounds)

   This study investigated the evolution of strain and temperature fields of a NiTiHf High-Temperature Shape Memory Alloy (HTSMA) undergoing complex thermomechanical loads involving simultaneous stress and temperature changes. In situ Digital Image Correlation (DIC) was used to track strain due to combined phase transformation and plastic yielding. Two types of loadings were performed: out-of-phase (OP) involving a simultaneous increase of stress and decrease of temperature and in-phase (IP) involving a simultaneous increase of stress and temperature. Five cycles were performed for each path. Due to a temperature gradient in the samples during the experiments, transformation nucleated in regions with the adequate temperature at a given stress level. Results showed a smooth transformation behavior for out-of-phase loadings along with a concentration of residual strain where transformation fronts meet one another. Due to the simultaneous high stress and high temperature for in-phase paths, creep was identified as a significant deformation mechanism for those paths. Furthermore, DIC allowed us to identify twinning/detwinning regions within the samples. Partial phase diagrams of the alloy were generated using the test results. Those experiments demonstrated the feasibility of characterizing HTSMAs using thermo-mechanical cycling to gain insights into the couplings between thermally- and mechanically-induced solid-state phase transformations for combined loading paths. 

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