37. Development of Concrete Building Cutting Technology Using HIgh-Power Laser

S. GOYA a, H. MORI b, T. OKUDA b , Y. FUJIYA c, N. SHIMONABE d, T. AKABA e

a)Research Manager, Manufacturing Technology Research Department, Research & Innovation Center, Mitsubishi Heavy Industries, Ltd. 

b)Manufacturing Technology Research Department, Research & Innovation Center, Mitsubishi Heavy Industries, Ltd. 

c)Senior Manager, Manufacturing Technology Research Department, Research & Innovation Center, Mitsubishi Heavy Industries, Ltd. 

d)Chief Staff Manager, Nuclear Plant Component Designing Department, Nuclear Energy Systems, Mitsubishi Heavy Industries, Ltd. 

e)Manager, Research & Development Department, Nuclear Plant Service Engineering Co., Ltd. 

With the increasing power and better quality of laser oscillators, laser processing, which has not been applied to thick concrete, has been increasingly used in recent years. In this report, we describe laser cutting of thick concrete columns (with a maximum thickness of 1200 mm) by using high-power fiber laser of over 20 kW and an ultra-long focus optical system, aiming at establishing a remote demolition technology for nuclear plant buildings that are high radiation areas. This report also describes a new beam laser damper system using water that was developed as a technology for receiving the high-power laser beam passing through a cutting object, which has been an issue in high-power laser processing. 

36. Surface ablation efficiency and quality of fs lasers in single-pulse mode, fs lasers in burst mode, and ns lasers

M. Domke a, V. Matylitsky b, S. Stroj a 

a)Josef Ressel Center for Material Processing with Ultrashort Pulsed Lasers, Research, Center for Microtechnology, Vorarlberg University of Applied Sciences, Hochschulstr. 1, Dornbirn 6850, Austria 

b)Spectra-Physics, Feldgut 9, Rankweil 6830, Austria 

In recent years, the burst-mode caught a lot of attention in the field of ultrashort-pulse laser micro machining. One of the major issues is the influence of the burst pulse number and frequency on ablation efficiency and quality. A recent publication reported of a significant increase in ablation efficiency when processing with ≥25 burst pulses at ≥100 MHz burst frequencies. This raises the question of whether processing with such high pulse densities can be attributed to non-thermal ablation, or whether a quasi-nanosecond laser ablation behavior is achieved. To answer this question, we determined ablation efficiencies as function of fluence for silicon, stainless steel, and copper and compared the ablation quality at the optimal fluence using the following laser systems: femtosecond laser operated in single-pulse mode, fs laser operated in 28-pulse-burst mode with a burst pulse frequency of 148 MHz, and a nanosecond laser with a pulse duration of 175 ns, which is identical with the temporal length of the burst pulse train. The comparison showed that the burst mode used produces similar surface morphologies and melt burrs as the nanosecond laser, but at about 2/3 of its efficiency. 

35. Ultra vibration assisted laser (UVAL) treatment of copper for superhydrophobicity

Menglei Zhao a, Zeng Yang a, Jingnan Zhao a b, Pranav Shrotriya a b c, Yan Wang a b, Yuanchen Cui d, Zhiquan Guo a b 

a)Tianjin University of Science and Technology, Tianjin, China

b)Tianjin Key Laboratory of Integrated Design and On-line Monitoring for Light Industry & Food Machinery and Equipment, Tianjin, China

c)Iowa State University, Department of Mechanical Engineering, Ames, USA

d)U. S. Polyco, Ennis, USA

In this paper, a hybrid ultrasonic vibration assisted laser (UVAL) prepared copper surface of super-hydrophobic was reported. After UVAL treatment, the water contact angle (WCA) of copper surface to 3 μL water was 157.4°and the water slip angle (WSA) was less than 10°. The wettability, microstructure, chemical composition and durability of copper surface were measured by contact angle measuring instrument, field emission scanning electron microscopy (FESEM), surface predatory X-ray diffraction (XRD) and three-dimensional morphology. The results revealed that after UVAL treatment, the microcoral-like structure and nano-grass structure were formed on the surface of the sample, which were similar to the surface of lotus leaf. Ultrasonic vibration combined with laser treatment can accelerate the adsorption of airborne hydrocarbon contaminations on the surface of micro and nanostructures, and reduce the surface energy of copper particles on the surface. This study provides a fast, convenient and effective method for the rapid preparation of stable superhydrophobic copper surface. 

34. Development and testing of a laser-based decontamination system

A. Anthofer*, W. Lipopmann and A. Hurtado

Chari of Hydrogen and Nuclear Engineering, Institute of Power Engineering, Technische Universitaet Dresden, Germany

Decontamination of radioactive concrete surfaces may be necessary during operation or decommissioning of nuclear power plants. Usually only the upper layers of the concrete structure are contaminated and are removed using labor-intensive mechanical milling processes. Production of a large amount of dust, which can lead to secondary contamination, is inherent to these processes. Improvements in high-energy laser technology have now made it possible for laser radiation to be used in decontamination technologies for the removal of concrete layers. A decontamination unit comprising a diode laser with a beam power of 10 kW in continuous wave (CW) mode in combination with an autonomous manipulator was developed for use in nuclear plants. The laser beam melts the concrete surface to a depth of approximately 5 mm. Compressed air jets then detach the molten layer from the concrete surface and convey it to a suction system, with which it is transported to a collection container. Most of the radionuclides are trapped in the solidifying melt particles, which form an extremely stable effluent well suited to long-term storage. A relatively small amount of dust is generated in the process. Because there is no backlash during energy transfer, the laser device carrier can be designed to be lightweight and flexible. A specially developed manipulator that can move freely along walls and ceilings by means of suction plates is used for the carrier unit. This results in short setup times for preparing for use of the device and minimal personnel exposure to the radiation. Experiments were conducted on a concrete wall to demonstrate the functionality of the overall system in realistic conditions. An optimal ablation rate of 2.16 m2 /h at an ablation depth of 1–5 mm was achieved. Today’s commercially available diode lasers with powers higher than 50 kW enable ablation rates of 410 m2 /h to be achieved and hence make these laser-based systems competitive alternatives to mechanical systems.

33. A laboratory study about laser perforation of concrete for application in oil and gas wells

H. Kariminezhad1) , H. Amani2) and M. Moosapoor1)

1)Department of Physics, Babol University of Technology, Babol, Iran

2)Faculty of Chemical Engineering, Babol University of Technology, Babol, Iran

Laser perforation is the application of light to make a flow path between wellbore regions through the casing wall and cement layer all the way to reservoir production zone. Due to significant losses of laser power at long distances, introducing a novel method in order to facilitate laser perforation in oil and gas reservoirs is necessary. This paper aims to study on concrete perforation using a continuous 240 W/cm2 CO2 laser. In this research, the effect of water on the parameters of laser perforation such as rate of perforation (ROP), specific energy (SE) and dominant mechanisms was investigated. For this, two groups of concrete samples (dry and wet) were illuminated at 2, 6, 15, 30 and 60 s by the laser. Our results showed evaporation was main mechanism for dry samples at exposure times above 15 s, while spallation was the dominant mechanism for the wet samples at all exposure times. ROP and SE were significantly increased and decreased in the presence of moisture, respectively. Maximum ROPs obtained 2.26 mm/s and 0.45 mm/s for wet and dry samples, respectively. Also, minimum of SEs for wet and dry samples obtained 1.05 J/mm3 and 4.3 J/mm3, respectively. Finally, our experimental results were justified using a simplified heat conduction model. All these characteristics demonstrate presence of water in concrete possesses an important role to improve rate of laser perforation. Therefore, the results of this research could significantly reduce time and cost of laser perforation for application of oil recovery. 

32. Using a High-Power Fibre Laser to Cut Concrete

K. Nagai1) and K. Shimizu1)

1)Department of Architecture and Architectural Engineering, College of Industrial Technology, Nihon University, Japan

Concrete cutting at construction sites causes problems such as noise, vibration, and dust. In particular, during the demolition and renovation work on buildings in urban areas, protection against noise, vibration, dust, etc., is needed. Concrete cutting using a CO2 laser was investigated 20 years ago. However, this method had never used because the equipment is difficult to carry. In this study, we used a portable fibre laser, which is convenient to carry. Two types of concretes with different strengths were prepared for the experiment. High-strength concrete has never been used in similar research before. High-strength concrete is just only used for skyscrapers because of its high quality and cost. Furthermore, it has already been used for skyscrapers in Japan. It is for this reason that we chose to use it in this study. Irradiation measurements were conducted under various conditions using laser powers of 6 and 9 kW. It was confirmed that the cutting effectiveness of CO2 and fibre las ers was approximately identical for concretes with a thickness of 200 mm. Furthermore, the cutting effectiveness for the two concretes with different densities was almost the same. However, the situation after cutting was different because the vitrification of the cutting and glass formation progressed in low-density concrete and an explosion phenomenon occurred in high-density concrete, simultaneously. This study suggests that laser concrete cutting can be used as a solution when noise and dust are major problems. 

31. Laser weldability of cast and rolled high-entropy alloys for cryogenic applications

H. Nam1), C. Park1), J. Moon3), Y. Na2), H. Kim3), and N. Kang1)

1)Department of Materials Science and Engineering, Pusan National University, Republic of Korea

2)Titanium Department, Korea Institute of Materials Science, Republic of Korea

3)Department of Materials Science and Engineering, Pusan UniversityNational University, Republic of Korea

Laser similar welding of cast and rolled high-entropy alloys (HEAs) was performed using the cantor system (Co0.2Cr0.2Fe0.2Mn0.2Ni0.2). As the welding velocity was increased from 6 to 10 m min−1, the shrinkage voids, primary dendrite arm spacing, and dendrite packet size decreased, thus improving the mechanical properties of the cast and rolled HEA welds. The cast HEA welds showed tensile properties comparable to those of the base metal (BM). In all the specimens fracture occurred near the heat-affected zone and BM at 298 K. However, the rolled HEA welds showed lower tensile strength than the BM, and fracture occurred in the weld metal (WM). This can be attributed to the larger dendrite packet size of the WM than the grain size of the BM. In addition, the tensile properties of the specimens at the cryogenic temperature were superior to those observed at 298 K, regardless of the cast and rolled HEA welds. This is because the formation of deformation twins and dislocations was predominant at 77 K. Therefore, the laser similar welds of cast and rolled HEAs are suitable for cryogenic applications. 

30. Microstructure and properties of Laser Surface Remelting AlCoCrFeNi2.1 HighEntropy Alloy

J. Chen1), J. Zhang1), K. Li2), D. Zhuang2), Q. Zang3), H. Chen3), Y. Lu4), B. Xu4) and Y. Zhang1)

1)School of metallurgy and materials engineering, Jiangsu University of Science and Technology, China

2)School of materials science and technology, Jiangsu University, China

3)School of materials science and technology, Jiangsu University of Science and Technology, China

4)Suzhou institute of technology, Jiangsu University of Science and Technology

In this study, laser surface remelting of an AlCoCrFeNi2.1 high-entropy alloy was performed using a Yb:YAG laser. The effects of laser surface remelting on the phase structure, microstructure, Vickers hardness, frictional wear properties, and corrosion resistance of the high-entropy alloy were investigated. The remelted layer of the AlCoCrFeNi2.1 high-entropy alloy was produced by remelting at 750 W laser power and formed a good metallurgical bond with the substrate. The X-ray diffraction results showed that the 750 W remelted layer consisted of face-centered cubic and body-centered cubic phases, which were consistent with the phases of the as-cast AlCoCrFeNi2.1 high-entropy alloy, and a new phase was not generated within the remelted layer. Laser surface remelting is very effective in refining the lamellar structure, and the 750 W remelted layer shows a finer lamellar structure compared to the matrix. The surface hardness and wear resistance of the AlCoCrFeNi2.1 high-entropy alloy were substantially improved after laser surface remelting. In a 3.5 wt.% NaCl solution, the laser-remelted surface had a larger self-corrosion potential and smaller self-corrosion current density, and the corrosion resistance was better than that of the as-cast high-entropy alloy. 

29. Colorizing metals with femtosecond laser pulses

A. Y. Vorobyev1) and  C. Guo1)

1)The institute of optics, University of Rochester, USA

This research team has demonstrated, visually and through spectral measurements, the creation of color metals with femtosecond laser surface structuring technique. We show that our technique essentially provides a controllable modification of optical properties of metals from UV to terahertz via surface structuring on the nano-, micro-, and submillimeter-length scales. The size of the optically modified metal surface area can be as small as a tightly focused laser spot, i.e., down to about 10 m, or as large as needed when a scanning laser beam is used. Given the additional advantages of laser processing such as low contamination and the capability to process complicated shapes, the color metals created in this work have tremendous potential in various technological applications. 

28. Effect of silica fume content in concrete blocks on laser-induced explosive spalling behavior 

Seong Y. Oh1), Gwon Lim1), Sungmo Nam1), Byung-Seon Choi1)

1)Korea Atomic Energy Research Institute

The experimental study is conducted to investigate the effect of silica fume mixed in concrete blocks on laser-induced explosion behavior. We use a 5 kW fiber laser as a thermal source to induce explosive spalling on a concrete surface blended with and without silica fume. An analytical approach based on the difference in the removal rate and thermal behavior is used to determine the effect of silica fume on laser-induced explosive spalling. A scanner is employed to calculate the laser-scabbled volume of the concrete surface to derive the removal rate. The removal rate of the concrete mixed with silica fume is higher than that of without silica fume. Thermal images acquired while scabbling is used to qualitatively analyze the thermal response of laser-induced explosive spalling on the concrete surface. At the early stage of laser heating, an uneven spatial distribution of surface temperature appears on the concrete, including silica fume, because of frequent explosive spalling within a small area. By contrast, in laser-heated concrete without silica fume, the spalling frequency is relatively lower, and a larger area is removed via one explosive spalling event owing to its high porosity. 

17. Laser decontamination of epoxy painted concrete surfaces in nuclear plants

원전 내 에폭시 도색 콘크리트 표면의 레이저 제염

A. Anthofer, W. Lippmann, A. Hurtado

Laser technology offers an efficient decontamination of surfaces contaminated by polychlorinated biphenyls (PCB) by precise application of highly focused laser beam power. In the context of nuclear decommissioning all walls and floors of a reactor building have to be cleaned from chemical-toxic substances. State of the art is a manual and mechanic ablation and a subsequent treatment in a hazardous waste incinerator. In this study, alternatively, a laser-based system exhibiting, decontamination rates of up to 6.4 m^2/h has been operated using a 10-kW diode laser in continuous wave (CW)mode with a spot size of 45 X 10 mm^2 and a wavelength of 980–1030 nm. The system allows a rapid heating of the surfaces up to temperatures of more than 1000 celsius degree leading to ablation and thermal decomposition of PCB  in one process step. Thermal quenching prevents formation of polychlorinated dioxines (PCDD) and polychlorinate furans (PCDF) in the flue gas. Additionally, an in situ measurement system based on laser induced fluorescence (LIF) is developed to monitor the thermal decomposition of PCB. Forinitial experiments samples covered with epoxy paint were used to evaluate the process and to carry out finite element based simulations. In this paper, experimental results of ablation tests by laser irradiation of epoxy painted concrete are presented and discussed.

16. Ultra-high power (100kW) fiber laser welding of steel

철의 초-고출력 (100kW) 파이버 레이저 용접

YOUSUKE KAWAHITO, HONGZE WANG, SEIJI KATAYAMA, AND DAICHI SUMIMORI

    A 100 kW fiber laser was first used to weld steel. Speeds at the range between 0.3 and 5.0 m/min were tested, and the maximum weld bead depth of 70 mm was achieved by single pass welding. Solidification cracking and porosity occurred when the welding speed was lower than 0.5 m/min, while undercut appeared when the welding speed was higher than 3.0 m/min. Both the ratio of depth to width and the cross section area of the weld bead had a positively linear relationship with the welding speed. A high speed camera was used to observe the characteristics of the keyhole and molten pool. The average number of spatters increased with the welding speed, while the keyhole diameter and the length of the molten pool in front of the keyhole decreased with the welding speed. This Letter validates the application potential of a 100 kW ultra high power fiber laser in manufacturing, e.g., welding, cutting, and additive manufacturing.

15. Studies on enhanced thermally stable high strength concrete incorporating silica nanoparticles

실리카 나노입자가 함유된 열안전성이 향상된 고강도 콘크리트에 관한 연구

R. Kumar, S. Singh*, L.P. Singh

 The performance of silica nanoparticles incorporated high strength concrete (SNPs-HSC) has been evaluated under elevated temperature conditions by exposing up to 800  C, followed by cooling to ambient temperature before performing experiments. Time-temperature studies revealed that incorporation of silica nanoparticles (SNPs) in concrete mix delays the heat transfer by 11%, 18%, 22% and 15% at 200  C, 400  C, 600  C and 800  C respectively thereby, decreasing the rate of degradation as compared to the conventional high strength concrete (HSC). A reduction in weight loss was observed in SNPs- HSC specimens after exposure to 200  C, 600  C, and 800  C; whereas at 400  C the weight loss quantity was  3.5% higher than the control HSC specimens due to the evaporation of water from calcium silicate hydrate (C-S-H) gel. On exposure up to 400  C for 2 h, the compressive strength and split-tensile strength increased by 40% and 13% respectively, for SNPs-HSC specimens, whereas in control HSC specimen’s strength didn’t increase after 200  C. A higher residual compressive (7%) and split-tensile strength (8%) was found to be in SNPs-HSC specimens exposed to 800  C for 2 h as compared to the control HSC specimens. The stress-strain curves revealed that SNPs-HSC specimens exhibits brittle failure up to 600  C whereas in control HSC brittle failure was observed only up to 400  C. Microstructural studies performed on the samples taken from the core of the 400  C exposed SNPs-HSC revealed the formation of higher C-S-H content and lower amount of calcium hydroxide (CH) leading to their enhanced mechanical and thermal stability. 

14. Laser scabbling of mortars

모르타르의 레이저저 스케블링

B. Peach*, M. Petkovski*, J. Blackburn, D.L. Engelberg

Laser scabbling of concrete is the process by which the surface layer of concrete may be removed through the use of a low power density laser beam. Previous research has suggested that the driving force responsible for laser scabbling is developed within the mortar. The aim of this investigation was to establish the key parameters that influence laser scabbling of mortars. All scabbling tests were carried out using an IPG photonics YLS-5000 (5kW) Yb-fibre laser. the specimens were subjected to a static, continuous, diverging laser beam with a stand off distance of 340mm from the focal point which gave a nominal beam diameter of 50mm. Tests were conducted with the laser beam applied to a vertical concrete surface to avoid debris falling back onto the specimen during testing. The results show that the removal of free water from mortars prohibits scabbling, but resaturation allows mortar to scabble. A reduced permeability, either due to a reduction in the water/binder ratio or the use of 25% PFA replacement, enhances the scabbling. A higher fine aggregate content increases volume removal and fragment sizes during laser scabbling.

13. Laser cutting of aluminium-alumina metal matrix composite

알루미늄-알루미나 금속 메트릭스 복합체의 레이저 절단

S. Marimuthu, J. Dunleavey, Y. Liu, M. Antar, B. Smith

Laser cutting of monolithic materials like metals and alloys is well-established and is used extensively in various industries including aerospace, medical and automotive. However, laser cutting of anisotropic materials like metal matrix composites (MMC) is challenging due to the differences in the chemical and physical properties of the matrix and fibre reinforcement. This manuscript contains details and results of an investigation into laser cutting of 2mm thick aluminium metal matrix reinforced with aluminium oxide fibre (Al MMC). The laser cutting mechanism and the influence of laser cutting parameters on the quality of cuts were examined in detail. The experimental results demonstrated that the laser cutting mechanisms of fibre reinforced MMCs are vastly different from the mechanisms observed in laser cutting of monolithic metals and alloys. The Al2O3 fibres within the MMC are not vaporized but are removed along with the molten, low melting point matrix materials. A thin and uniform layer of Al2O3 was been deposited over the cut surface which can be advantageous for applications that involve moving gases or fluids, for example, aero-engine cooling holes.

12. Surface Cleaning of Metals Using Low Power Fiber Laser

저출력 fiber laser를 이용한 금속 표면 세정

E. KAYAHAN, L. CANDAN, M.ARAS and O. GUNDOGDU

Lasers are used in industry in a large variety of applications. These applications can mainly be divided into two categories: one specifically being materials processing. Material processing includes cutting, drilling, welding, etc., and generally involves the use of high-powered lasers. Laser applications such as rust/dye removal and surface cleaning are not yet very common for the industry. This paper reports experiments on industrial applications of a ytterbium fiber laser (1064 nm) with a maximum output power of 20 W, pulse duration of 200 ns and pulse repetition rate of 10-100 kHz. Furthermore, the laser beam was focused on the target through a 160 mm focal length F-T lens. Scanning speed and line spacing of laser are 3-100 mm/s and 1-100 um, respectively. Experimental studies showed that a low-power fiber laser could be used for a variety of applications such as surface cleaning of metals and rust-dye removal. Optimum laser parameters were also determined for these applications.

11. High-Power Fibre Laser Cleaning for Green Shipbuilding

 G. X. Chen, T. J. Kwee, K. P. Tan, Y. S. Choo and M. H. Hong

Blasting techniques in shipbuilding and ship repair have been developed for surface preparation of steel to a standard equivalent to SA2.5 as defined by ISO Standard 8501. The usage of consuma-bles, such as abrasive materials, air and water, constitutes a recurring cost in these processes. When blasting work is carried out in the open space, such as during a dry docking, abrasive blasting gen-erates a lot of dusts which in turn pollutes the environment with consequential social and economi-cal costs. Laser blasting or laser cleaning, which has not been introduced commercially in shipbuild-ing and ship repair, offers an alternative for green manufacturing and green repairs. Laser cleaning has significant advantages on these issues over the conventional blasting techniques. It is a well-controlled process with unique properties, such as precise treatment, high selectivity, and high flexi-bility. A cleaning technique using a high-power fibre laser is developed for the surface preparation of steel. Fibre laser has advantages of compact system, automation capability, and low maintenance cost. We report the laser cleaning results using a 500-W pulsed high-power fibre laser. The laser cleaning is able to meet the SA 2.5 requirements of blast cleaning as described in the International Organization for Standardization (ISO) standard 8501.

10. Microstructural analysis of interfacial transition zone (ITZ) and its impact on the compressive strength of lightweight concretes

Interfacial transition zone (ITZ)의 미세 구조 해석과 경량 콘크리트의 압축강도에 미치는 영향 

P. Vargas, Oscar Restrepo-Baena, Jorge I. Tobón

   Lock-in thermography and heat flow measurements with peltier sensor(TEC-1089-SV) was performed during fatigue crack growth testing. Moreover, elastic stress fields (E-Amplitude) as well as dissipated energies (D-Amplitude) can be determined. In case of thermographic measurements the specimens have to be painted to enhance the emissivity, but the thickness of the coating influences the results and therefore quantitative measurements are problematic. The heat flow measurements are easy to perform and provide quantitative results, but only integral values in an area given by the size of the peltier element can be achieved. In order to get comparable results the evaluation of the thermographic measurements were performed in the same area as the peltier measurements. In case of the mean temperature measured by thermography and the heat flow determined with the peltier sensor a good agreement was found. The measurement of elastic stresses with the peltier sensor is restricted to low loading frequencies due to the response characteristic of the sensor. For the measurement of dissipated energies the cooling of the specimen by heat conduction into the clamps and heat radiation has to be taken into account.

8. Investigation on rock breaking for sandstone with high power density laser beam

고출력 레이저 빔을 이용한 사암 암석 파괴에 대한 조사

Meiyan Li, Bin Han, Qi Zhang, Shiyi Zhang, Qingkun He

6. Experimental Investigation of Multi-mode Fiber Laser Cutting Cement Mortar

다중 모드 광섬유 절단 시멘트 모르타르의 실험적 연구

D. K. Lee, S. H. Pyo