Murthy Kolluri

Verified

Murthy verified their affiliation via an institutional email.

Learn more

Verified

Murthy verified their affiliation via an institutional email.

Learn more

• Ph.D
• Senion Research Consultant at NRG, Nuclear Research & consultancy Group

The integrity assessment of the Reactor Pressure Vessel (RPV) is essential for the safe and Long Term Operation (LTO) of a Nuclear Power Plant (NPP). Hardening and embrittlement of RPV caused by neutron irradiation and thermal ageing are main reasons for mechanical properties degradation during the operation of an NPP. The thermal ageing-induced de...

Within the framework of the European Fusion Development Agreement (EFDA), an EU batch of oxide-dispersion-strengthened (ODS) Eurofer97 steel samples have been irradiated with neutrons to nominal dose levels of 1 and 3 displacements per atom (dpa) in the High Flux Reactor (HFR) located in Petten to investigate irradiation induced changes in the micr...

Prevention of delamination failures by improved design calls for accurate characterization and prediction of mixed-mode interface delamination. In this paper, a combined in situ experimental-numerical approach is presented to fully characterize the interface behavior for delamination prediction. The approach is demonstrated on two types of industri...

An experimental investigation into the constant stress amplitude compression-compression fatigue behavior of closed-cell aluminum foam, both with and without lateral constraint, was conducted. Results show that while the early stages of strain accumulation due to fatigue loading are independent of constraint, the rapid strain accumulation stage beh...

In the past few years, miniature testing techniques to evaluate the mechanical properties of structural materials of nuclear reactors have gained interest due to the limited number of irradiated surveillance specimens and strict safety regulations. One of such miniature testing techniques is the Small Punch Testing (SPT) method, which uses tiny dis...

Assessing the embrittlement and hardening of reactor pressure vessel steels is critical for the extension of the service lifetime of nuclear power plants. This paper summarises the tensile test results on the irradiation behaviour of realistic VVER-1000 welds from the STRUMAT-LTO project. The welds were irradiated at the HFR (Petten, the Netherland...

The present paper provides a summary of an inter-laboratory round robin on the fracture toughness testing and Master Curve application on unirradiated materials. First, a validation exercise was performed on the analysis of a given force-displacement curve. Then, a validation exercise was performed on the application of the Master Curve procedure o...

Surveillance testing is the basis for all reactor pressure vessel (RPV) integrity and lifetime assessments to evaluate the validity of the RPV embrittlement trend curve used for a specific reactor. Most of the standard surveillance programmes, do not contain sufficient number of surveillance specimens for beyond the original design life of 40 years...

One of the main points of any project implementation is the dissemination of the obtained results among the nuclear community, young researchers, public, stakeholders, etc. Communication and dissemination activities are considered as high-priority elements in European collaborative research projects. The article briefly presents EUROATOM project “S...

Miniature / sub-sized specimen test methods for the mechanical characterization of metallic alloys like the small punch test (SPT) have the benefit that only small quantities of material are needed to perform a reasonable number of tests. This makes such tests in particular interesting if only limited quantities of material are available for mechan...

Understanding the mechanical behaviour of reactor pressure vessel (RPV) steels at high fluences has become an important topic in regard to Long-Term Operations (LTO) of existing nuclear power plants (NPP). The effectiveness of thermal annealing treatments to recover the mechanical properties of compositionally tailored pressurised water reactor (PW...

A number of surveillance programs for pressurized water reactor (PWR)-type reactors do not contain enough surveillance samples for their long-term operation (LTO) beyond the original design life of 40 years. The use of testing methods based on small/sub-sized specimen is considered a promising approach to overcome this limitation. In addition, smal...

Most standard surveillance programs for pressurized water reactors (PWR), do not contain enough surveillance specimens for their long-term operation (LTO) beyond the original design life of 40 years. The use of testing methods based on small/sub-sized specimen such as mini-CT (0.16 CT, 4 mm thickness) is considered a promising approach to overcome...

Understanding the irradiation induced degradation of the reactor pressure vessel (RPV) steels at high fluences becomes more important in view of safe long term operation (LTO) of existing nuclear power plants. Specifically, the role of Ni, Mn and Si and associated synergetic effects on embrittlement behaviour need to be further investigated to unde...

Mechanical testing and microstructural investigation on VVER-440 15Cr2MoV welds were carried out after irradiation and after recovery annealing treatment at two different temperatures (340°C and 475°C) for 100h. The welds are part of the last surveillance chain of an Armenian nuclear power plant and have been irradiated for ∼200,000h at 270°C, rece...

The small punch (SP) test technique is expected to become a more common tool for estimating tensile properties since the technique has been approved for standardization and will be published early 2020 as EN-10371. The testing technique is naturally of interest in the nuclear field due to the small amount of material needed for estimating the prope...

The reactor vessel of the High Flux Reactor (HFR) in Petten has been fabricated from Al 5154-O alloy grade with a maximum Mg content of 3.5 wt. %. The vessel experiences large amount of neutron fluences (notably at hot spot), of the order of 1027 n/m2, during its operational life. Substantial damage to the material’s microstructure and mechanical p...

Eurofer97 is a candidate structural material for nuclear fusion reactors. To better understand the ageing effects due to radiation during long-term use in real fusion conditions, Eurofer97 was neutron irradiated at the High Flux Reactor in The Netherlands. TEM images of post-irradiation Eurofer97 reveal a high density of irradiation-induced disloca...

The reactor vessel of the High Flux Reactor (HFR) in Petten has been fabricated from Al 5154 - O alloy grade with a maximum Mg content of 3.5 wt. %. The vessel experiences large amount of neutron fluences (notably at hot spot), of the order of 1027 n/m2, during its operational life. Substantial damage to the material’s microstructure and mechanical...

A literature review on highly irradiated 5xxx and 6xxx series Al alloys is conducted to understand the expected changes in mechanical properties of high flux reactor (HFR) vessel material in relation with microstructural aspects beyond the current surveillance data to support the HFR Surveillance Program (SURP). It was found that the irradiation sw...

Alloy 800H is considered as a candidate material for intermediate heat exchanger (IHX) components of (very) high temperature reactors (V)HTRs. Qualification of the this alloy for the aforementioned nuclear applications requires understanding of its high temperature tensile, low-cycle fatigue behavior and creep-fatigue interactions because the IHX c...

A TEM investigation of an EU batch of oxide dispersed strengthened (ODS) Eurofer97 steel specimens, irradiated to 1 and 3 dpa at 300, 450 and 550°C in high flux reactor at Petten, has been performed to understand the influence of irradiation temperature on the characteristics of irradiation defects and, eventually, on the resulting mechanical prope...

Delamination is often identified as an important failure mechanism in structures with a high interface density, such as modern microelectronic systems and advanced composite materials. Delamination tests performed on different interface structures reveal complex failure mechanisms (crack bridging, fibre pull out, micro-void coalescence, fibrilation...

Interfacial delamination is a key reliability challenge in composites and micro-electronic systems due to (high density) integration of dissimilar materials. Predictive finite element models require the input of interface properties, often determined with an interface delamination growth experiment with (nearly) constant process zone, relying on th...

Cohesive zone models are common tools for the simulation of delamination since two decades. However, application of these models in a quasi-static finite element framework requires a sufficiently fine discretization to resolve a quasi-brittle process zone. As an alternative to mesh refinement, an adaptive approximation of the growing delamination w...

Interfacial delamination is a key reliability challenge in composites and micro-electronic systems due to (high density) integration of dissimilar materials. Predictive finite element models are used during the design and optimization stage to minimize delamination failures, however, they requires a relevant interface model to capture the (irrevers...

Precise characterization of interface delamination in miniature interface structures is an ongoing challenge with the advent of miniaturization and multi-functionality in the electronics industry. Accurate numerical prediction of the interface behavior is necessary to minimize delamination failures. Successful prediction requires (i) accurate deter...

System-In-Package (SIP) microsystems, contain several interfaces formed between stacked, multiple, thin layers, manufactured using different materials and processes. Interface delamination is often recognized as a critical failure mechanism concerning the reliability of these products due to the high stresses at the interfaces. Accurate measurement...

The crush bands that form during plastic deformation of closed-cell metal foams are often inclined at 11-20 degrees to the loading axis, allowing for shear displacement of one part of the foam with respect to the other. Such displacement is prevented by the presence of a lateral constraint. This was analysed in this study, which shows that resistan...

A new miniature mixed mode bending (MMMB) setup for in-situ characterization of interface delamination in miniature multi-layer structures was designed and realized. This setup consists of a novel test configuration to accomplish the full range of mode mixities and was specially designed with sufficiently small dimensions to fit in the chamber of a...

A novel test frame configuration was developed and employed to design a new miniature mixed mode bending (MMMB) setup for in-situ characterization of interface delamination in miniature multi-layer structures to accomplish full range of mode mixities. This advanced setup is specially designed with sufficiently small dimensions to fit in a scanning...

A new miniature test setup capable of in-situ characterization of interface delamination is designed and constructed. Two unique features of the newly designed setup are its compactness to fit under a scanning electron microscope (SEM) and its ability to trigger delamination in bilayer samples over a full range of mode mixity from pure mode I to mo...

It was reported recently that closed cell A1 foams exhibit strain hardening when subjected to monotonic or cyclic loading with lateral constraint. In the present study compressive and fatigue testing was carried out on some A1poras foams with lateral constraint. The deformation mechanisms responsible for this behaviour were examined in this study,...

An experimental investigation into the effect of lateral constraint on mechanical properties of a closed-cell Al foam, Alporas, was conducted. Results show that while the initial plastic strength of the foam is unaffected, the constraint induces significant strain hardening as plastic deformation progresses. The strain hardening is also sensitive t...

Experimental results, presented in the companion article, show that the compressive deformation of a closed-cell Al foam under lateral constraint is characterized by significant strain hardening. This enhanced hardening is due to the change in stress state from uniaxial to triaxial, which additionally contributes to friction between the deforming f...