bluuebunny/crossref_metadata_2025 huggingface dataset:
A modular diagnosis system based on fuzzy logic for UASB reactors treating sewage
Authors: Borges R. M. , Mattedi A. , Munaro C. J. , Franci Gonçalves R.
Published: April 2016

A modular diagnosis system (MDS), based on the framework of fuzzy logic, is proposed for upflow anaerobic sludge blanket (UASB) reactors treating sewage. In module 1, turbidity and rainfall information are used to estimate the influent organic content. In module 2, a dynamic fuzzy model is used to estimate the current biogas production from on-line measured variables, such as daily average temperature and the previous biogas flow rate, as well as the organic load. Finally, in module 3, all the information above and the residual value between the measured and estimated biogas production are used to provide diagnostic information about the operation status of the plant. The MDS was validated through its application to two pilot UASB reactors and the results showed that the tool can provide useful diagnoses to avoid plant failures.
Temporary Stabilization with External Fixator in ‘Tripolar’ Configuration in Two Steps Treatment of Tibial Pilon Fractures
Authors: Daghino Walter , Messina Marco , Filipponi Marco , Alessandro Massè
Published: April 2016

Background:

The tibial pilon fractures represent a complex therapeutic problem for the orthopedic surgeon, given the frequent complications and outcomes disabling. The recent medical literature indicates that the best strategy to reduce amount of complications in tibial pilon fractures is two-stages procedure. We describe our experience in the primary stabilization of these fractures.

Methods:

We treated 36 cases with temporary external fixation in a simple configuration, called "tripolar": this is an essential structure (only three screws and three rods), that is possible to perform even without the availability of X-rays and with simple anesthesia or sedation.

Results:

We found a sufficient mechanical stability for the nursing post-operative, in absence of intraoperative and postoperative problems. The time between trauma and temporary stabilization ranged between 3 and 144 hours; surgical average time was 8.4 minutes. Definitive treatment was carried out with a delay of a minimum of 4 and a maximum of 15 days from the temporary stabilization, always without problems, both in case of ORIF (open reduction, internal fixation) or circular external fixation

Conclusion:

Temporary stabilization with external fixator in ‘tripolar’ configuration seems to be the most effective strategy in two steps treatment of tibial pilon fractures. These preliminary encouraging results must be confirmed by further studies with more cases.
Depression and CD4 Cell Count Among Patients With HIV in a Nigerian University Teaching Hospital
Authors: Olisah Victor Obiajulu , Adekeye Oluwatosin , Sheikh Taiwo Lateef
Published: April 2016

Objective

Depression is common in people living with HIV/AIDS and there is some evidence that depressive symptoms may have adverse effects on immune functioning. The purpose of this study was to determine the prevalence of current depressive disorder in patients with HIV/AIDS and its association with CD4 cell count.

Methods

A consecutive sample of 310 patients with HIV/AIDS attending Out-patient clinic in Ahmadu Bello University Teaching Hospital (A.B.U.T.H.), Zaria, Nigeria was assessed. The Center for Epidemiologic Studies Depression Scale (CES-D) was used to screen for depressive symptoms, and the Schedule for Clinical Assessment in Neuropsychiatry (SCAN) was used to confirm the diagnosis of current depressive disorder. The CD4 cell counts of participants with depressive disorder were compared with those of participants without depressive disorder. Multiple regression analysis was conducted to identify socio-demographic and disease-related factors associated with depression.

Results

Among the 310 HIV-infected participants assessed for depression, 14.2% had current depressive disorder. Adjusting for age, gender, education, occupation, and marital status, patients with CD4 counts < 150 cells/μl were more likely to be depressed.

Conclusion

Depression is common among HIV-infected persons in Nigeria and is associated with low CD4 cell counts. The screening and treatment of mental health problems such as depression should be considered an integral component of HIV care and support.
Religious Involvement, Suicidal Ideation and Behavior in Mainland China
Authors: Wang Zhizhong , Koenig Harold G. , Ma Wanrui , Liu Lan
Published: April 2016

Objective:

Little is known about relations between religious involvement and suicidal behaviors in mainland China. This study aims to examine the association between religious involvement and suicidal ideation, planning, and attempts within a general community population controlling for socio-demographic, physical, and mental health factors.

Method:

Data were examined from a population-based sample of 2,769 community-dwelling adults in the province of Ningxia China, where nearly 40% are Muslim, 11% other religious affiliations, and 49% no religion. Four separate logistic regression models examined correlations between religious involvement and self-reported suicidal thoughts, plans, and attempts. Analyses were also stratified by Muslim affiliation ( n = 1103) and no religion ( n = 1,366).

Results:

Bivariate analyses in the overall sample demonstrated that higher personal religiosity scores (χ2 = 6.8, p < 0.01) and total religiosity scores (χ2 = 5.1, p < 0.05) were positively correlated with developing a suicidal plan, which disappeared after controlling for demographic characteristics. Otherwise, no significant correlations were found between any religious characteristic and suicidal ideation, plan, or attempt in either Muslims or those with no religion.

Conclusions:

In contrast to most previous studies, religious involvement plays less of a role in suicidal behaviors in at least one province of mainland China.
HLA-DQ Mismatches and Rejection in Kidney Transplant Recipients
Authors: Lim Wai H. , Chapman Jeremy R. , Coates Patrick T. , Lewis Joshua R. , Russ Graeme R. , Watson Narelle , Holdsworth Rhonda , Wong Germaine
Published: April 2016

Background and objectives

The current allocation algorithm for deceased donor kidney transplantation takes into consideration HLA mismatches at the ABDR loci but not HLA mismatches at other loci, including HLA-DQ. However, the independent effects of incompatibilities for the closely linked HLA-DQ antigens in the context of HLA-DR antigen matched and mismatched allografts are uncertain. We aimed to determine the effect of HLA-DQ mismatches on renal allograft outcomes.

Design, setting, participants, & measurements

Using data from the Australia and New Zealand Dialysis and Transplant Registry, we examined the association between HLA-DQ mismatches and acute rejections in primary live and deceased donor kidney transplant recipients between 2004 and 2012 using adjusted Cox regression models.

Results

Of the 788 recipients followed for a median of 2.8 years (resulting in 2891 person-years), 321 (40.7%) and 467 (59.3%) received zero and one or two HLA-DQ mismatched kidneys, respectively. Compared with recipients who have received zero HLA-DQ mismatched kidneys, those who have received one or two HLA-DQ mismatched kidneys experienced greater numbers of any rejection (50 of 321 versus 117 of 467; P<0.01), late rejections (occurring >6 months post-transplant; 8 of 321 versus 27 of 467; P=0.03), and antibody-mediated rejections (AMRs; 12 of 321 versus 38 of 467; P=0.01). Compared with recipients of zero HLA-DQ mismatched kidneys, the adjusted hazard ratios for any and late rejections in recipients who had received one or two HLA-DQ mismatched kidneys were 1.54 (95% confidence interval [95% CI], 1.08 to 2.19) and 2.85 (95% CI, 1.05 to 7.75), respectively. HLA-DR was an effect modifier between HLA-DQ mismatches and AMR (P value for interaction =0.02), such that the association between HLA-DQ mismatches and AMR was statistically significant in those who have received one or two HLA-DR mismatched kidneys, with adjusted hazard ratio of 2.50 (95% CI, 1.05 to 5.94).

Conclusions

HLA-DQ mismatches are associated with acute rejection, independent of HLA-ABDR mismatches and initial immunosuppression. Clinicians should be aware of the potential importance of HLA-DQ matching in the assessment of immunologic risk in kidney transplant recipients.
Childcare Teachers' Job Satisfaction: Effects Of Personality, Conflict-handling, and Organizational Characteristics
Authors: Kim Sanglim , Yang Sungeun
Published: April 2016

We aimed to examine the comprehensive effects of individual personality traits, interpersonal conflict-handling styles, and organizational characteristics on job satisfaction as perceived by childcare teachers. The sample comprised 179 childcare teachers in South Korea. Survey results
revealed that organizational characteristics, such as rewards, director support, collegial relationships, and participation in organizational decision making, positively affected job satisfaction. In addition, job satisfaction was increased by the influence dimension of personality profiles,
whereas it was not significantly influenced by conflict-handling styles. The findings in this study suggest that the structural and operating conditions of childcare centers should be improved to increase teachers' job satisfaction.
Effect of Product Presentation Order and Purchase Quantity on Consumers' Additional Purchase Behavior
Authors: Kim Jonghum , Park Eun-A , Kim Hayea
Published: April 2016

We examined how presentation order and purchase quantity affect the purchase intention of consumers and the amount of information they search for in regard to target products. Participants (N = 122) were students at universities in the Republic of Korea who were assigned to 1
of 3 types of experimental condition. The effects of presentation order were tested in conditions where the number of products being purchased was small. The effects of purchase quantity were examined in conditions where the number of products being purchased was larger. Results showed that
when a small number of items made up the purchase presentation order this had an effect on purchase intention but did not affect the amount of information the participants searched for about the target products. When participants were purchasing a large number of products this increased the
intention to purchase the target product and decreased the amount of information search performed. Our findings in this study have an important implication for irrational consumerism in that buying a large number of products led to consumers more readily making unplanned additional purchases.
Effects of Individuals' Motivations on Communications in Online Health Forums
Authors: Wu Bing , Jiang Shan , Chen Hsinchun
Published: April 2016

Our aim was to analyze the effects of individuals' motivations, specifically reciprocity, experience, activity, and emotion, on their communications in an online health forum. We employed an exponential random graph approach to analyze concrete models embedded in online health networks.
According to the research that we conducted over a 5-year period on a dataset drawn from a global diabetes forum, reciprocal information diffusion occurred in the forum; a high level of online activity had a positive impact for gratification of the individual user. Both having more experience
and expressing polarized emotions played an important role in individuals' post contributions, however these factors had little influence on reply interaction among users. We also modeled post contribution and reply interaction in the same network in respect to the relationship-building processes,
which may help in gaining more understanding about the mechanisms underlying communication in online health forums.
Love for One's Country or Oneself: A Brand-choice Framework in Emerging Markets
Authors: Zhu Xiaodong , Yu Chunling , Hu Saiquan
Published: April 2016

We utilized 185 Chinese survey responses to evaluate the effects of national brand consciousness (NBC) and self–brand connection (SBC) on Chinese consumer preferences. We used linear models, and our analyses established two key effects. First, NBC was positively related to Chinese
consumers' attitudes toward national brands and negatively related to foreign brands. Second, SBC exerted a positive influence on Chinese consumers' attitudes toward both national and foreign brands. Whereas quality judgments moderated their attitude toward national brands, psychological distance
between consumer and brand moderated their attitude toward foreign brands. The relationship between brand attitude and purchase intention was also positive. Finally, we have suggested branding strategies for both Chinese and foreign firms operating in the Chinese market.
A review paper on offline inspection of finished and semi-finished products and emerging research directions
Authors: Babar Ramzan , Wook Kang , Sarkar Biswajit
Published: April 2016

Organizations want to focus on product quality along with productivity to
get their competitive advantage in global market. In order to achieve this
aim, quality management system and its different aspects are becoming more
valuable than before. This study has considered quality control and its
activities with specific focus on offline inspection. The objective of this
study is to provide a literature review that identifies different models and
methodologies, developed for offline inspection under different
manufacturing and inspection conditions. This review is based on research
work accepted by international journals and published in the years from 2000
to 2016. These studies are classified into six groups on the basis of their
research objectives, model developed, adopted methodologies, and research
outcomes. This review paper also gives ? brief look at the offline
inspection to propose future research opportunities and emerging trends. The
proposed research directions can be helpful in developing new models or
modifying the existing models to improve the performance of offline
inspection.
The Impact of Estimate Source and Social Pressure on Auditors' Fair Value Estimate Choices
Authors: Brink Alisa G. , Tang Fengchun , Yang Ling
Published: April 2016

This paper reports the results of an experiment examining whether estimate source (developed by an external consultant or the audit client) interacts with social pressure (obedience pressure from a superior or conformity pressure from a peer) to influence Chinese auditors' judgments of fair value estimates. The results reveal an interaction between the source of the estimate and the type of social pressure. Specifically, Chinese auditors' risk assessments and judgments regarding whether an auditor will investigate further are not influenced by relevant information about a fair value estimate's source when advised to use a questionable estimate by a superior. However, when the same advice is received from a peer, the likelihood of further investigation and auditors' risk assessments are impacted by the estimate's source.
Laser cutting of composites—Two approaches toward an industrial establishment
Authors: Staehr R. , Bluemel S. , Jaeschke P. , Suttmann O. , Overmeyer L.
Published: April 2016

Carbon fiber reinforced plastics (CFRP) are of high interest as a lightweight material due to their high strength-to-weight ratio. Within industrial fields with a requirement on lightweight design and energy efficiency, the demand of CFRP increases continuously. Up to now, the cutting of CFRP, as a basic production step within the production of composite parts, is mainly performed by conventional cutting techniques such as milling and abrasive water jet cutting. These techniques are known to have drawbacks, e.g., force input, handling of auxiliaries, and tool wear. The laser cutting of CFRP has already shown high potential to be a practical alternative due to the wear-free and contactless processing. However, as a thermal technique, laser cutting has to overcome the challenge of heat input into the material. Two different approaches concerning deterioration free cutting will be examined and compared within this research. For that purpose, two different laser sources were used. Both laser sources have a maximum average laser power of PL = 1500 W, one emitting continuous wave and the other emitting pulsed wave. The first approach investigated is the laser cutting with a single mode fiber laser emitting continuous wave at high beam quality. A small focal diameter was achieved by the optical setup used, enabling narrow cutting kerfs and finely machined cutting contours. The relative movement of laser beam and material was realized by a combination of scanning optic and three precise linear stages. The second laser source is a high power thin-disk laser emitting nanosecond pulses. The optical setup consists of a fiber with a diameter of d = 600 μm and a galvanometer scanner by TRUMPF, called 3D programmable focusing optic (PFO-3D), leading to a focal diameter bigger than that of the single mode fiber laser. The relative movement was realized by the PFO-3D and a six-axis robot system. The required process strategies, differences, benefits, and drawbacks of both setups will be reviewed. The review will be completed by an examination of the complexity of the setups and introduction of efficient processing solutions. Comparative investigations with an identical material for both described setups were performed as a basis for discussion. Differences exist in appearance of the cuts and the choice of best parameters, while comparable qualities and efficiencies can be achieved for both setups.
Morphology evolution of γ′ phase in K465 nickel-base superalloy during laser forming repairing
Authors: Li Qiuge , Lin Xin , Wang Xinghua , Yang Haiou , Huang Weidong
Published: April 2016

Laser forming repairing (LFR) was performed on the damaged K465 nickel-base cast superalloy parts. LFR presented the uneven microstructure characteristics at different positions of the LFRed K465 superalloy, such as substrate zone (SZ), heat affected zone (HAZ), and repaired zone (RZ), which experienced the different thermal history. Compared with the coarser γ′ precipitates in the cast SZ, the γ′ precipitates in RZ were refined obviously. As for HAZ, γ′ phase presented an incomplete solid solution and reprecipitation growth characteristics. This led to an increase in the microhardness from SZ, HAZ to RZ.
Accuracy of calculated component distortions using the weld pool length to calibrate the heat source
Authors: Belitzki Alexander , Zaeh Michael F.
Published: April 2016

A better understanding of the laser welding process is fundamental for improving the quality of welded components. Hence, an experimental analysis, as well as an increase of the accuracy of computational approaches is important. When using a structural simulation to predict the component distortions caused by a welding process, it is necessary to reconstruct the temperature field. The use of heat source models is an established approach for the reconstruction of the temperature. This work is focused on evaluating the accuracy of calculated component distortions using the weld pool length to calibrate the heat source. For the implementation, image processing tools and an automated algorithm to calibrate the heat source are used. The experiments were carried out using an adapted intensity distribution which results from superimposing the beams of a high-power diode laser and a neodymium-doped yttrium aluminum garnet (Nd:YAG) laser. To observe the process in general and the weld pool in particular, a high-speed camera was used. The image data was subsequently analyzed by an algorithm to extract the transient weld pool length. To simulate the laser welding process in an FEA-tool, a parameter calibration of two double ellipsoid heat sources, based on optimization algorithms, was used. To compare the computational and the experimental results, the component distortions were measured by position sensors. The results of the study are shown and the relevance of implementing the weld pool length to calibrate the heat source is pointed out.
Investigations on ultra-high-speed laser material deposition as alternative for hard chrome plating and thermal spraying
Authors: Schopphoven Thomas , Gasser Andres , Wissenbach Konrad , Poprawe Reinhart
Published: April 2016

The development of new coating technologies for the wear and corrosion protection of large, high-quality components in the manufacturing industry is becoming more significant, not only from an economic but also from an ecological perspective. In various branches such as aerospace, oil and gas, automotive, papermaking, and others, hard chrome plating (HCP) is a widespread, standard process. However, the implementations of EU directives such as 1999/13/EC (VOC), 2011/65/EU (RoHS), and 2012/19/EU (WEEE) as well as the EU regulation EC 1907/2006 (REACH) to environmental protection, to environmental protection, CO2-reduction, and energy efficiency are leading to considerable market upheavals in the future. In HCP, toxic and carcinogenic hexavalent chromium (Cr6+) is used, which can only be used with authorization after the so-called sunset date in September 2017. Similar applies to the use of nickel in electroplating have been classified as dangerous for the environment and toxic by the World Health Organization. Coating technologies which are considered capable of replacing HCP are thermal spray technologies, especially high-velocity oxygen-fuel (HVOF) thermal spraying and laser material deposition (LMD). With HVOF thermal spraying, coatings out of a large range of materials can be applied, which feature high wear resistance at relatively low investment costs. Nevertheless, thermal spray coatings are technologically constrained in regard to limited adhesion strength due to the poor mechanical bonding between coating and substrate. Moreover, thermal spray coatings are typically difficult to repair and often exhibit porosity levels in the range of 1%–2%. In the production of wear and corrosion protection layers, LMD is only established in individual applications. With LMD, high-quality pore- and crack-free coatings out of a large range of materials can be produced with metallurgical bonding and low dilution. However, typical coating thicknesses (>500 μm) are commonly too large for the wear and corrosion protection and attainable surface rates in the range of 10–50 cm2/min far too small for the coating of large components. In this paper, a novel approach for LMD of Inconel 625 with surface rates up to 500 cm2/min and deposition speeds up to 200 m/min is presented. The influence of the main processing parameters on layer thickness and appearance of bonding zone is investigated. With this new process variant much thinner, pore- and crack-free wear and corrosion protection layers with a thickness in the range of approximately 10–250 μm can be produced.
Laser beam welding of ultrahigh strength martensitic steels with active cooling
Authors: Gerhards Benjamin , Reisgen Uwe , Olschok Simon
Published: April 2016

Recent steel developments create new possibilities for steel construction and lightweight design. The reason for this is the ultrahigh strength of particular steel grades. Fully martensitic steels like 22MnB5 or S1100 QL gain ultimate yield strengths of up to 1500 MPa. Therefore, those grades are predestined for crash relevant or highly loaded parts, and they gain increasing importance as construction materials. As promising as the martensitic ultrahigh strength steels are as construction materials, there are some issues when it comes to joining. The heat input into the material harms the costly adjusted material properties. Thus, each welding process reduces the strength in the heat-affected zone considerably. The key to reduce the drop in strength is to conduct the welding heat out of the work piece. The quicker the heat is conducted the lesser it can harm the material properties. Therefore, it is vital to select an active cooling device capable of conducting a large amount of heat out of the work piece in a very short period. Preliminary tests have shown that it is possible to reduce the width of the heat-affected zone to 50%. Therefore, the work pieces were cooled by liquid nitrogen before and straight after the welding process. To improve the cooling conditions, a clamping device including the possibility of active cooling via water or a mixture of liquid and gaseous nitrogen is designed. The clamping jaws are made out of copper for the maximum heat conduction, and it is possible to cool the weld seam directly through a nitrogen gas flow. Combined with a cooling device which mixes fluid and gaseous nitrogen, gas temperatures down to −150 °C are technically feasible. The setup is used to join martensitic steels by laser beam welding. The effects of a temperature range from room temperature down to −50 °C on the mechanical properties are investigated and discussed.
Modeling of weld pool phenomena in tungsten inert gas, CO2-laser and hybrid (TIG+CO2-laser) welding
Authors: Krivtsun Igor , Reisgen Uwe , Semenov Oleksii , Zabirov Alexander
Published: April 2016

The efficiency of the welding process in terms of weld penetration and weld width is greatly determined by the heat, mass, and charge transfer phenomena in the weld pool. These phenomena, in turn, depend on the thermal and electromagnetic interaction of the heat source used with the metal being welded. The most adequate models of the welding processes should consider the interaction of the phenomena in the heat source, on the base metal surface and inside its volume by a self-consistent way. This paper is devoted to the development of a self-consistent model of weld pool dynamics in tungsten inert gas (TIG), laser and hybrid (laser + TIG) spot welding without a keyhole formation. The proposed model allows simulation of processes taking place in the weld pool and on its surface. The model takes into account free surface deformation, influence of plasma shear stress, thermocapillary Marangoni effect, and Lorentz forces on the weld pool, as well as of the processes in the arc plasma including laser-arc interaction. For this purpose, the model of the weld pool is combined with a model of arc plasma column where the interaction processes between Gaussian beam radiation emitted by a continuous-wave CO2 laser and the argon arc plasma are described. The equations of the model proposed are solved numerically by means of finite element method. The simulation results are compared with real welding experiments performed with steel S-235JR. A good accordance between simulation and experimental results is observed.
Laser soldering and brazing of steel-aluminum sheets for tailored hybrid tubes
Authors: Nothdurft Sarah , Springer André , Kaierle Stefan , Ross Jonathan , Stonis Malte
Published: April 2016

Lightweight construction plays an important role in meeting the increasing demands of the automotive industry regarding weight reduction. In this work, two approaches have been chosen: weight reduction based on material and weight reduction based on design. Steel and aluminum are used for the first approach, and hydroforming is the method used for design optimization by shaping. Mixed material seams of steel and aluminum have been generated using laser soldering and laser brazing to make steel-aluminum tailored hybrid tubes for hydroforming. The seam has to provide sufficient formability and strength. The main difficulty in joining steel and aluminum is the formation of intermetallic phases, and these hard and brittle phases have to be avoided to ensure good forming properties. Pyrometric temperature detection for power control and longitudinal beam oscillation can provide an appropriate temperature-time profile to reduce the heat input, and consequently the intermetallic phases. Tests have been performed for joining aluminum (EN AW-6xxx, EN AW-7xxx) and two different galvanized steels. The sheet thickness was 1 and 2 mm for each material, and combinations of the same and different sheet thicknesses were tested. Another variation is edge preparation for different geometries and qualities. In this paper, the results of the joining process are described.
Into polarization control in laser cutting with direct diode lasers
Authors: C. Rodrigues Gonçalo , Duflou Joost R.
Published: April 2016

Laser cutting of metal sheets with direct diode lasers (DDL) has recently proven to be feasible, showing industrial relevant cutting speeds at acceptable cutting quality. Further developments are still required to optimize the cutting performance of such technology before it can be considered as an alternative to CO2 or fiber laser variants. In this paper, laser polarization control is studied as a strategy to enhance the cutting performance of such lasers systems. For this purpose, two DDL sources, with output powers in the range of 750 W, have been installed in an experimental gantry platform which allows an independent control of common cutting parameters (focal point position, stand-of-distance, cutting speed, nozzle opening, gas selection, and gas pressure). Different optical designs and combinations of optical components were used to obtain a set of spatial polarization arrangements, including: linear-, cross-, azimuthal-, and radial-polarizations schemes. A series of experiments on different materials (stainless steel 304 L and 316 L and steel S355) were done to verify the influence of such configurations on laser cutting of metals with both reactive and nonreactive gases. Influence of polarization on the cutting results is found to be very high when cutting with a nonreactive gas, such as nitrogen, while the same effects are less evident when a reactive gas, oxygen, is used. Focal point position and material composition are found to significantly influence the performance obtained with the different polarization schemes. Axes of symmetry of the tested polarization strategies and directionality dependence of the cutting results are taken into account and discussed in this paper, while different strategies are proposed to improve their applicability.
Research status and development of laser shock peening
Authors: Xu Yujie , Du Zhenying , Ruan Liang , Zhang Wenwu
Published: April 2016

Laser shock peening (LSP) is a noncontact surface strengthening technology. It has been widely used because of its advantages in applied scope and strengthening effects. LSP has made considerable progress during the past four decades, but some technical issues affecting their applications remain to be resolved, for instance, the utilization rate of laser shock energy is only about 50%, the processing adaptability of rigid confinement layer is poor, and the thickness of the flexible confinement layer represented by a water layer is difficult to control. In this paper, the current research status of LSP technology was reviewed, and an outlook was given toward further development of this technology. On this basis, a method to form composite shock waves by designing a cavity to confine the water layer is presented in this paper, which is expected to address the issues mentioned above. A preliminary simulation for analyzing the relationship between the strengthening effect and the characteristic parameters of the composite shock wave was carried out, and the simulated results were discussed. The results show that the time interval between the adjacent waves and the wave attenuation factor have significant influence on the strengthening effects, which is helpful to the cavity design.
Vision-based keyhole detection in laser full penetration welding process
Authors: Zhao Hongbo , Qi Huan
Published: April 2016

In a laser full penetration welding process, keyhole behavior affects the welding quality most. Due to the variation of wall thickness, constant welding speed and power will lead to partial penetration or over heat. So, effective monitoring and control method is needed to improve the quality of laser full penetration welding. In this paper, a vision based full penetration hole detection system is studied. The effects of exposure time, zooming lens, and optical filters on the quality of coaxial images are investigated. Among these factors, narrow bandwidth filters affect coaxial images most, because according to Plank law, workpiece under different temperature will emit light of different wavelengths, and the images under different narrow bandwidth filters reflect the temperature distribution of workpiece. The full penetration hole detection algorithm is developed based on region grow algorithm. Images of different welding speed and power are captured, and the relationship of the diameter of full penetration hole with welding speed and laser power is studied. The detection algorithm can identify partial penetration welding and laser cutting. It can be used to closed loop control of laser welding in future.
Metallurgical response of weld metal to different filler metal and joint design combinations of laser-arc hybrid welded lean duplex and novel ferritic stainless steels
Authors: Karhu Miikka , Kujanpää Veli , Romu Jyrki , Sarikka Teemu
Published: April 2016

Laser and laser-arc hybrid welding of duplex and ferritic stainless steels is demanding, because microstructure of the welds tends to be highly ferritic. Therefore, filler metal must be used for maintaining corrosion and mechanical properties of the welds. In this study, different filler metals including duplex, basic, and overalloyed austenitic grades were used with laser-arc hybrid method to weld lean duplex 1.4162 and novel ferritic stainless steels grades 1.4622 and 1.4509. Several sets of joint design and welding parameter combinations were used to adjust the amount of filler metal in the weld. The purpose of the trials was to evaluate whether weld metal microstructures (grain morphology, austenite/ferrite balance, etc.) can be modified by using an applicable joint preparation and an “overmatched” filler metal addition. Weld characterization included several research methods such as: Macro- and microscopic examination using light microscope¸ cross-sectional dilution ratio determination from the metallographic cross sections, electron backscatter diffraction method in order to assess austenite, and ferrite phase proportions in the test welds. The effects of used groove geometry, filler metal composition, and content on resulting metallurgical features of the welds are discussed in detail.
Experimental research of hybrid welding processes in combination of gas tungsten arc with CO2- or Yb:YAG-laser beam
Authors: Reisgen Uwe , Krivtsun Igor , Gerhards Benjamin , Zabirov Alexander
Published: April 2016

Hybrid welding is a field in welding technology in which several welding procedures are combined to operate in one weld bath. An attempt is being made to combine the positive properties of the processes in a way that synergy effects take place and can be taken advantage of. Comparative experimental analysis of hybrid welding processes is carried out. The used hybrid welding process is a combination of tungsten cathode in argon shielding gas atmosphere and laser beam of different wave lengths (CO2- and Yb:YAG laser). Both lasers were used in heat transfer mode, without keyhole. To carry out these experiments, a special hybrid welding torch was developed to combine arc and laser heat sources in one common weld pool. Depth of penetration and the area of welds' cross sections for pure tungsten inert gas (TIG), TIG plus CO2 laser, and TIG plus Yb:YAG laser were compared. High-speed video images (500 frames per second) with synchronized current and voltage recording were used. The experimental results demonstrate a different behavior of the arc in CO2- and Yb:YAG laser hybrid welding. It is shown that in case of hybrid welding the efficiency of input energy from the arc is higher than the sum of two separately used heat sources.
Comparison of three different arc modes for laser-arc hybrid welding steel
Authors: Frostevarg Jan
Published: April 2016

Traditionally, Laser Arc-Hybrid Welding (LAHW) is made using a gas metal arc heat source in pulsed mode. In this study, welds made with three different arc modes under various conditions are compared. The arc modes compared for LAHW are: Standard, Pulsed, and Cold Metal Transfer (CMT). The pulsed mode, using power modulation, is more controlled than the “natural” Standard mode and offers globular drop transfer with reduced heat input to the work piece, enabling thinner materials to be welded. The CMT arc mode also uses power modulation as well as controlled wire feeding. This enables surface tension drop transfer, involving even less heat input and is also considered to generate less undercuts and spatter than the other two arc modes. The welds compared were made in 7 mm thick S420 laser cut steel sheets with two different welding speeds and gap sizes. They were made using close-to-production setup within the limitations of the CMT capabilities, i.e., low and medium wire feed rates. The weld caps and roots were studied optically and the structures were analyzed by making cross-sectional macrographs longitudinally and transversally. These cross sections were analyzed geometrically, structurally, and also hardness tested. The welds were also studied and analyzed by means of pre- and postweld scanning as well as high speed imaging. The study shows that the laser keyhole reduces the effect of the arc modes, enabling higher welding speeds than without the laser. The gouge formed in front of the keyhole determines occurrence of undercuts and bead uniformity. The material mixing of filler and base material, and laser penetration spiking is also influenced by the depth of the arc gouge. The material structure is also affected to some degrees for expected performances. Even though the short-arc technique CMT show promising results, the pros and cons for each arc technique are discussed.
Process-structure-property relationship of laser-joined thermoplastic metal hybrids
Authors: Amend Philipp , Mallmann Guilherme , Roth Stephan , Schmitt Robert , Schmidt Michael
Published: April 2016

During the last years, several studies have been conducted to improve the laser-based heat conduction joining of thermoplastic metal hybrids. Most scientists tried to improve the joint quality by a prior surface enlargement of the metal in order to achieve a strong mechanical interlocking. Only a few authors investigated hybrids which consist of merely cleaned and not additionally enlarged metallic specimens. For merely cleaned specimens, Katayama et al. postulated the bubble theory which suggests that small bubbles near the metallic interface are very important for strong joints. The bubble formation leads to a high pressure between thermoplastic and metal so that the thermoplastic melt wets the metallic surface and an anchor effect occurs. Investigations by the author confirm the anchor effect theory, but the bubble theory itself cannot be verified since strong joints can be realized without the formation of bubbles. On the contrary, it seems rather advisable to avoid bubbles because they indicate a thermal decomposition of the plastic. However, there is still no sufficient description of the relationship between process parameters, joint morphology, and resulting joint strength. The main objective of this paper is to point out the process-structure-property relationship of laser-based joined thermoplastic metal hybrids.
Nonlinear absorption measurements of intraocular lens polymers by integrating Z-scan
Authors: Heberle Johannes , Häfner Tom , Schmidt Michael
Published: April 2016

An ultrashort pulsed laser processing knowledge of the amount and distribution of the absorbed energy in the workpiece is essential. For transparent dielectrics, energy input by ultrashort laser pulses occurs by nonlinear absorption in the bulk material. Even at high intensities, the penetration depth is high and for most cases decays with an unknown function. Additionally, nonlinear absorptivity dramatically changes depending on the number of incident pulses due to incubation of the workpiece. This is usually attributed to chemical modifications or generated voids inside the workpiece. Particularly, polymers are strongly influenced by incubation preventing full understanding of ablation at industrial processes. Especially, the Polymethylmethacrylate (PMMA) copolymer analyzed in this paper is of high interest for ophthalmic applications and requires high processing quality and efficiency. To gain detailed insight into interaction of polymers with multiple subsequent picosecond laser pulses, investigations on nonlinear absorptivity have to be carried out. Therefore, the determination of nonlinear transmittance and reflectance by a modified Z-scan setup is presented. Laser pulses at 1064 nm wavelength, which are commonly used for production, are applied with pulse energies up to 130 μJ. Measuring the absorptivity depending on the pulse number is enabled by integrating spheres included in the setup. Up to 100 lasers pulses which are scattered by the rough surface, caused by ablation of previous pulses, are taken into account by collecting the scattered proportion by the spheres. A significant change of transmittance and reflectance is observed depending on the pulse energy and pulse number. The influence of incubation on nonlinear absorption is quantified by fitting the recorded data to the models known from literature. The analytical model of three-photon absorption shows best agreement and is considered as the dominant absorption process. The corresponding nonlinear absorption coefficients are quantified in dependence of the pulse number showing significant increase for the first six pulses.
Laser surface modification for the prevention of biofouling by infection causing Escherichia Coli
Authors: Gillett Alice , Waugh David , Lawrence Jonathan , Swainson Mark , Dixon Ron
Published: April 2016

Bacteria have evolved to become proficient at adapting to both extracellular and environmental conditions, which has made it possible for them to attach and subsequently form biofilms on varying surfaces. This has resulted in major health concerns and economic burden in both hospital and industrial environments. Surfaces which prevent this bacterial fouling through their physical structure represent a key area of research for the development of antibacterial surfaces for many different environments. Laser surface treatment provides a potential candidate for the production of antibiofouling surfaces for wide ranging surface applications within healthcare and industrial disciplines. In the present study, a KrF 248 nm Excimer laser was utilized to surface pattern polyethylene terephthalate (PET). The surface topography and roughness were determined with the use of a Micromeasure 2, 3D profiler. Escherichia coli (E. coli) growth was analyzed at high shear flow using a CDC Biofilm reactor for 48 h, scanning electron microscopy was used to determine morphology and total viable counts were made. Through this work, it has been shown that the surface modification significantly influenced the distribution and morphology of the attached E. coli cells. What is more, it has been evidenced that the laser-modified PET has been shown to prevent E. coli cells from attaching themselves within the laser-induced micro-surface-features.
Influences on incubation in ps laser micromachining of steel alloys
Authors: Häfner Tom , Heberle Johannes , Dobler Michael , Schmidt Michael
Published: April 2016

Efficient and accurate generation of micro holes and feature geometries is one object of investigation in ultrashort pulse laser processing. Different analytical models exist to describe the relationship between energy input and removed volume. These models relate to the ablation threshold and the energy penetration depth representing material-dependent parameters. Both parameters are influenced by incubation. Against this background, incubation effects depending on the number of pulses applied on two steel alloys are presented in the paper. The ablation threshold and the energy penetration depth are analyzed by the zero-damage method and an analytical model based on Beer's law describing the crater depth. The pulse frequency is chosen to fP = 100 Hz to investigate incubation excluding the influence of temporal effects between subsequent pulses. The used ultrashort pulsed laser has a pulse duration of 10 ps and a wavelength of 1064 nm. Craters are generated with defined pulse numbers between N = 1 and N = 1000. Two commonly used steel alloys—the cold working steel 1.2379 and the austenitic stainless steel 1.4301—are investigated and compared. Additionally, the first one is investigated at two levels of hardness. All sample surfaces have the same initial average roughness Sa ≈ 0.02 μm which was realized by manual polishing. The comparison of two incubation models shows higher coincidence of the experimental results and the model proposed by Ashkenasi than for the model published by Jee, especially for pulse numbers N > 100. The linear optical penetration depths which are determined by ellipsometry measurements are larger than the energy penetration depths which are analyzed for the ablation regimes of the gentle phase. The main reasons for the pulse-number dependent decrease of the ablation threshold are investigated. Absorption changes due to surface modifications such as oxidation and generation of different surface morphologies which are observed by scanning electron microscope. The obtained results are the basis for further studies on incubation including temporal multipulse effects.
Surface structure formation in WE54 Mg alloy subjected to ultrafast laser texturing
Authors: Khadka Indira , Castagne Sylvie , Wang Zhongke , Zheng Hongyu
Published: April 2016

Pico- and femtosecond laser surface structuring of WE54 Mg alloy was investigated in this paper. In particular, the effective response of rare earth elements during laser structuring and the surface structure formation mechanisms were studied. A 10 W picosecond laser, having a wavelength of 1064 nm, and a 1.5 W femtosecond laser, having a wavelength of 795 nm, were used to irradiate WE54 surface to change the surface morphology. A number of pulses varying from 100 to 1500 were applied to create a crater at single and multiple points on the WE54 alloy surface in an air medium. Taylor Hobson profilometer and energy dispersive x-ray spectroscopy (EDS) techniques were employed in order to analyze the modification in surface morphology and chemical composition, respectively. A crater depth around 1.1 μm was measured by the profilometer. It was observed that a compound of yttrium and neodymium was formed during the process of rapid thermalization, which is investigated by x-ray diffraction. The surface portion containing yttrium was converted into a white crystal-like structure as observed by optical and scanning electron microscope (SEM). The white color compound of rare earth element is turned into gray, then dark, and is finally ablated from the surface with increasing scanning number and number of laser pulses. The change in color represents the change in optical properties of WE54. SEM analysis also revealed that no cracks were present on the laser structured surface; hence, stress effect on the surface can be neglected. Explosive vaporization of the substrate was observed in pico- and femtosecond laser structuring. The investigation on ultrafast laser structuring suggests that the surface properties created by laser structuring of WE54 can be controlled if proper laser processing is applied.