bluuebunny/crossref_metadata_2025 huggingface dataset:
Determination of welding heat source parameters for fem simulation based on temperature history and real bead shape
Authors: SZYNDLER J.
Published: April 2023

Abstract. To improve process understanding and increase the numerical prediction quality of a wire arc additive manufacturing (WAAM) process, this paper focuses on determining the parameters of a numerical model that reproduces an experimental setup of a welding process, with particular attention given to the actual shape of the weld bead. The dimensions of the heat source (HS) model in a welding process are determined based on experimentally measured weld pool sizes as well as temperature history at selected points below and adjacent to a weld seam. The whole experimental setup is accurately reproduced within the Simufact.Welding software and an optimization procedure is applied to obtain the best possible agreement between experimental and numerical results. A validated numerical model with reliable parameters for two heat sources is later used to predict and observe material behavior during the WAAM process of more complex parts.
Development of a method for performance characterisation of PEMEC process considering electrolyte temperature in case of hybrid polishing of 316L steel
Authors: KRZAK D.
Published: April 2023

Abstract. This work falls within the context of very rough parts (Ra > 10 µm) polishing using a new hybrid process called PEMEC, which combines a mechanical abrasion action (tribofinishing) and an anodic dissolution action (electrochemical polishing). The study of the performances of a polishing process requires the monitoring of the surface roughness, but also the monitoring of the dimensions and the shape of the parts. This paper proposes a new method for characterising polishing operations that enables all these criteria to be monitored in a single test. This method is applied to the study of the influence of the electrolyte temperature in the PEMEC process.
Modeling electrochemical machining based on effective parameters
Authors: WAIMANN J.
Published: April 2023

Abstract. The process of electrochemical machining uses chemical reactions to dissolve material of the surface layer. This special kind of processing avoids undesired microstructural changes in the surface, such as the formation of dislocations. ECM is thus a very promising processing technique for high-strength materials. To model the complex chemical reactions in a computationally efficient manner, an inner variable is introduced, which describes the dissolution level of the material. The evolution of the inner variable is formulated based on Faraday’s law of electrolysis. Furthermore, the use of an effective formulation of the necessary material parameters enables to consider this homogenized description of the dissolution process within an electrical finite element framework. Each effective material parameter is a result of classical mixture rules.
Effects of ultrasonic burnishing on the surface quality of corrosion-resistant tool steel using a hard-carbon-coated burnishing tool
Authors: HUUKI J.
Published: April 2023

Abstract. Ultrasonic burnishing is a relatively new and effective method for improving the surface finish of metal parts. Burnishing strongly affects the surface quality, improving surface properties such as, surface hardness and surface roughness. Previous studied have observed that changing some burnishing parameters significantly affects the burnished surface quality. In this research, using a carbon-coated burnishing tool, tangential misalignment angles were varied on a corrosion resistant tool steel that has not been previously investigated. Two different burnishing tools were used to study their effect on surface quality and surface hardness. The results revealed that coated tungsten carbide tool has produced superior surface finish compare to non-coated burnishing tool which is the new finding. It is rather surprising that surface roughness has not increased as it typically happens during burnishing but a clear surface roughness enhancement was observed. The results showed a clear improvement in surface roughness (80-86%), whereas surface hardness did not change significantly.
Out-of-autoclave molding of carbon fiber composites pipes with interlaminar carbon nanotubes
Authors: BELLISARIO D.
Published: April 2023

Abstract. Carbon fiber reinforced (CFR) composite rings with and without interlaminar carbon nanotubes (I-CNTs) were manufactured starting from high performance prepregs used in aeronautics. Nano-particles deposition was obtained by an innovative easily scalable procedure which does not affect composite processability. A CNTs-solvent solution was sonicated for an established time to reduce bulk CNTs agglomerates. The solution was poured on prepreg stripes and left at room temperature for solvent evacuation. The prepreg stripes were wrapped on steel pipe to obtain the annular configuration and manufactured by an out-of-autoclave (OOA) process. The consolidation pressure was applied through a thermo-shrinkable tube and curing occurred in oven. Stereomicroscopy and mechanical tests were performed on CFR and I-CNTs/CFR rings. A good adhesion among the plies was observed as well as the positive effects of CNTs deposition; an increase of 34%, 15% and 17% was obtained for the stiffness, the peak load and the fracture energy of the functionalized rings, respectively.
Two-step PM forging for precise fabrication of carbon fiber reinforced engineering plastic gears
Authors: AIZAWA T.
Published: April 2023

Abstract. Carbon fiber reinforced engineering plastic (CFREP) small-sized parts were fabricated by PM (Powder Metallurgy)-oriented forging process. This manufacturing procedure consisted of the green compaction and sinter-forging steps. In the first step, the CFREP powders were consolidated to a green compact with high density. This preform was further sinter-forged into a final product by hot stamping with the use of the induction heating unit. Hardness distribution was measured to describe the consolidation behavior with increasing the compression load, and to optimize the sinter-forging conditions for solidifying the green compact to the sintered product. X-ray tomography was utilized for non-destructive diagnosis on the residual pores and defects. The eight-teeth gear model was fabricated to demonstrate that two step procedure wrought well to yield the dense and defect-free gear with sufficient strength and integrity.
Modeling the shape of additive manufactured parts
Authors: BRUNI C.
Published: April 2023

Abstract. The additive manufactured parts can be made by the use of suitable layer thicknesses of the polymer in order to respect the requirements of a refined geometry and of a surface appearance of the physical object that should be as similar as possible to the original CAD model. An other important variable is the digital datum that can represent a key variable of the realization procedure. The methodology proposed and followed in the present investigation got the objective to get a physical model, through the information obtained by a 3D scanning device, taking into consideration not only the digital treatment but also the building direction to guide the FDM layer deposition in order to realize the required surface appearance. The profiles of the specimen in the digital environment were compared to each other before realizing. The physical object obtained after digital treatment was similar to the one obtained by the original CAD.
Insights on the use of PVB nanocomposites as energy directors in ultrasonic welding of epoxy composites
Authors: CILENTO F.
Published: April 2023

Abstract. The selection of an adequate coupling film for welding thermoset composites (TSC) is primary for improving the degree of automation in the composite industry. Ultrasonic welding (UW) is a well-established technique for joining composites and has recently been utilized in the aerospace and automotive industries. To achieve an efficient joining, the use of a polymer-based material placed at the welding interface called an energy director (ED) is required. The choice of the coupling layer material is linked to several requirements, such as processing temperature, high adhesion to the TSC adherend and mechanical strength of the resulting welded joints. Most importantly, the viscoelastic dissipation of the ED influences the heating mechanism and the joint behaviour since the hysteresis loops generated during welding are dissipated into viscoelastic heat. In this work, the authors investigated the possibility of using Poly-vinyl-butyral (PVB) reinforced with graphite nanoplatelets (GNPs) as a coupling layer in UW of TSC adherents, showing that an improvement of lap shear strength (LSS) of 80% with respect to neat PVB.
Effect of compression during post-treatment to improve the mechanical strength of printed carbon fiber/ PEKK composites
Authors: COMBETTES J.
Published: April 2023

Abstract. This work aims to understand the effect of consolidation on parts obtained by material-extrusion additive manufacturing process. Three plates were manufactured with carbon fiber/PEKK tapes. Two of them were consolidated under pressure at 334 and 360°C corresponding to the maximum of the melting peak and the end of the melting peak of PEKK respectively. Another plate did not undergo any post-treatment after printing, it is used as a reference. The parts were characterized to measure their porosity by density measurement and X-ray micro-computed tomography. Subsequently, short beam shear tests and dynamic mechanical analysis (DMA) tests were carried out to assess the influence of porosity on the mechanical strength of the plates. As expected, the interlaminar shear strength (ILSS) decreases when the porosity increases. The highest ILSS is obtained for the part consolidated at 360°C due to a lower porosity. The highest storage modulus is obtained for the part consolidated at 334°C whereas the loss factor indicates a lower glass transition for the same part. This could be explained by a lower degree of crystallinity as revealed by DSC, compared to the part consolidated at 360°C.
Multi-criteria decision model of sustainable industrial production: A case study on 3D printed carbon PA
Authors: ANDREOZZI M.
Published: April 2023

Abstract. In the Concurrent Engineering (CE) approach, several aspects of the life cycle of a product are considered at the same time during the design phase. This allows to respond more quickly to the market needs and improves the final products quality. However, with this approach, the design phase could result more time consuming and expensive and needs simple and easily applicable optimization models. For this reason, a new multi-criteria decision model is proposed in this paper. Additive manufacturing technologies for high performances polymers are gaining increasing interest as they are a valid option for the manufacturing of structural components. For these reasons, high performance 3D printed isogrid structures in short carbon fibers reinforced polyamide were selected as a case study. Production processes of as-printed and dried isogrid structures were carried out; mechanical characterization and environmental and cost analysis were performed on the considered scenarios. Following the proposed model, the results of the analyses were used to calculate a single value indicator for each product. In this way, it was possible to compare the different alternative and select the optimal solution.
Innovative self-learning disturbance compensation for straightening processes
Authors: BATHELT L.
Published: April 2023

Abstract. To increase the sustainability of forming processes such as punch bending, homogenization of the processed semi-finished product is an essential step in the manufacturing process. High-strength wire materials are usually available as strip material before being further processed in a forming process. For storage and transport, the material is coiled onto coils and transported to the customer. During the coiling process, residual stresses and plastic deformation are introduced into the wire. Thus, the final product quality is also influenced by the geometry of the coil. Straightening machines are used in production lines to compensate for these. Once a straightening machine has been set up, the settings for the roll positions are usually not changed. As a result, there is no reaction to material fluctuations, which means that the components to be produced do not meet the dimensional accuracy requirements. This leads to an increase in the rejection rate in manufacturing processes. To reduce the rejection rate, it is necessary to enable dynamic and flexible infeed of the straightening rollers. In this context, an innovative control concept with disturbance compensation was developed for the straightening process. The disturbance compensation uses a disturbance model that predicts the change in bending curvature over the coil radius. With this prediction, the straightening machine can be adjusted specifically. The roller positions are adjusted by a subordinate position control. The additional feedback from measured geometric product properties from the following punching-bending process enables the straightening machine to be adjusted even in the case of unforeseen fluctuations in the material properties. In this way, it is possible to react to any material fluctuations as required. This novel, demand-oriented adjustment of the straightening machine is expected to result in a high increase in the efficiency of the production process and a reduction of the rejection rate.
Biodegradable polymers for cosmetic packaging: A technical and life cycle perspective
Authors: MIFSUD S.
Published: April 2023

Abstract. The packaging industry is a significant contributor to the plastic pollution burdening our environment. One main issue with plastics is that they are designed to be durable, and so they persevere in the environment even after they have fulfilled their use. This study aims to analyse the potential benefits of switching to biodegradable and biobased polymers in the cosmetic packaging industry to lessen their environmental impact once disposed of. This assessment commenced with a sustainable material selection process to shortlist a set of viable biodegradable candidate materials (polylactic acid and wood plastic composites), for cosmetic compacts and then comparing them to acrylonitrile butadiene styrene as the benchmark material for this application. The functional, environmental and cost implications of such a change were quantified to validate the suitability of using biodegradable polymers. Functionally, polylactic acid and acrylonitrile butadiene styrene only passed the testing conducted making wood plastic composites an unviable option. wood plastic composites and polylactic acid were found to cost 40-53 per cent more than acrylonitrile butadiene styrene. In terms of the environmental impact, polylactic acid and wood plastic composites reduced the lifecycle impact by 18-30 per cent and the end-of-life impact by 26-42 per cent. The results obtained suggest great potential in shifting to such an alternative.
Modeling and control of tribological properties for subsequent forming process in skin-pass rolling
Authors: LI X.
Published: April 2023

Abstract. The surface roughness including average roughness (Ra) and peak number (RPc) after skin-pass rolling influences the strip’s product properties, such as its friction coefficient in the subsequent sheet metal forming process. In order to both ensure an optimal tribological behavior and fulfill the process requirements of the following forming steps, predefined roughness combinations of Ra and RPc should be attained in skin-pass rolling. In this work, a preliminary friction model relating friction and combination of Ra and RPc is determined using flat die drawing tests for DC04 steel. The model is validated by deep drawing tests and embedded in a roughness control system for skin-pass rolling. To show a proof of concept for independent control of tribological properties from strip thickness, a simulation framework is implemented in Matlab/Simulink. The results indicate that the friction coefficient can be controlled between 0.0924 and 0.1003 for the considered test scenario (which is) characterized by a normal pressure of 75kN and a relative speed of 10mm/s.
Experimental setup and method for the characterization of ply-ply adhesion for fiber-reinforced thermoplastics in melt
Authors: PIERIK R.
Published: April 2023

Abstract. Process simulation software for hot press forming is a vital tool for the development of complex continuous fiber-reinforced thermoplastic parts for structural applications. The simulation tools need to be accurate to truly facilitate the design stage, which in turn requires accurate material characterizations and constitutive models. The material forming behavior is composed of different deformation mechanisms, one of which is the separation of adjacent plies or delamination. Currently, the resistance against delamination or ply-ply adhesion is modeled as a constant tensile stress that needs to be overcome, the value of which is based on an educated guess. To date, no standard exists to characterize this material property for thermoplastic matrix composites (TPC) in melt. Hence, we discuss and evaluate several methods to measure ply-ply adhesion of TPCs. The most promising approach, a so-called probe test, was further pursued and a setup was designed and manufactured for the use in a rheometer. Subsequently, we measured the required normal force to separate two C/LM-PAEK tapes in melt. Repeated tests on the same specimen resulted in an increasing adhesive peak force, which we relate to a change in the amount and distribution of the matrix material at the ply’s surface. The peak force increased also with increasing compression time and pressure. We found a reasonable correlation of the average measured peak force with the values currently assumed in simulation software.
In-plane deformation measurements for validation of composite forming simulations
Authors: BRANDS D.
Published: April 2023

Abstract. Validation of composites forming simulations is essential to improve simulation predictions. Detailed validation requires reliable and well-controlled forming processes with precise methods for comparison to simulation results. This study presents some preliminary results from press forming experiments with cross-ply laminates shaped over a dome geometry. The material studied is a unidirectional carbon-fiber reinforced thermoplastic composite. The forming experiments were combined with a deformation measurement technique based on photogrammetry to measure the in-plane deformation on the surface of the laminate after forming. The obtained full-field deformation measurements allow for a direct and quantitative comparison with simulations. The accuracy and precision of the methodology are discussed in detail. The combination of a versatile forming experiment and a detailed analysis method as presented in this article could enable a more precise validation of composite forming simulations.
Prediction of surface topography change during chain of selective laser melting and burnishing
Authors: TEIMOURI R.
Published: April 2023

Abstract. The present study developed theoretical models for simulation of surface topography and roughness of parts produced by the selective laser melting (SLM) process and their evolution after burnishing as post-treatment. The simulation algorithm has been integrated by combining principles of selective laser melting process, i.e., formation of the melt pool and kinematic of motion, followed by mechanic of burnishing through Z-map approach. To verify the simulation results, 316L stainless steel was 3D printed and then burnished under different burnishing depth. 3D surface profile and surface roughness of as-printed material and those post-processed by surface burnishing (SB) were measured through microscopic examination and surface roughness measurement, respectively. The results obtained through comparison of confirmatory experiments and simulation model affirmed that the proposed approach is accurate enough to predict the surface topography and roughness of as-printed and post-treated samples.
An Inverse method for determining fabric permeability in vacuum assisted resin infusion for composite parts forming
Authors: VOSNIAKOS G-.C.
Published: April 2023

Abstract. Vacuum Assisted Resin Infusion (VARI) method employs a mould on top of which a number of fabric pieces are laid up and impregnated by resin drawn through vacuum. Simulation of VARI depends on the determination of fabric permeability. In this work, permeability value is selected from a set of discrete values by a genetic algorithm. An impregnation simulation model is run on ComsolTM to compute the flow front propagation inside the fabric. The genetic algorithm compares the evolution (propagation) of the impregnation front, in a space and time dimension, with the corresponding result of one single actual impregnation experiment, obtained by machine vision. A simple part suffices for this experiment assuming homogenous fabric porosity. The computational cost of the method is low, making it superior to experimental determination of permeability on expensive custom-made devices.
Effects of cold-drawing and low-temperature annealing on the sensing properties of NiTi alloys
Authors: LI Y.
Published: April 2023

Abstract. As an intelligent material, NiTi alloy exhibits shape memory effect and superelasticity. Its electrical resistance varies with deformation, thus making NiTi alloy a potential sensing material. Linearity and sensitivity are the two principal characteristics of sensors. Linearity reveals the deviation of the actual resistance-strain response from an ideal straight line and sensitivity is the change in input required to generate a unit change in output. Though conventional polycrystalline NiTi alloys possess high sensitivity and large strain range, the non-linear resistance-strain responses were not negligible thus hindering their sensing application. It was found that cold-drawing combing with low-temperature annealing had affected the linearity, while the influence rules were not clear. The electrical resistance of the fabricated NiTi alloy wires with various areal reductions were measured during stretching, and the results shown that the cold-drawn and annealed NiTi alloys exhibited better linearity though with decreased sensitivity. This investigation provides foundation for subsequent research on improving or tailoring the sensing properties of NiTi alloys.
Effects of disc milling and indirect extrusion processing on mechanical properties of aluminum-graphene-composites with commercial GNPs
Authors: NEGENDANK M.
Published: April 2023

Abstract. In this study aluminum-graphene-composites were manufactured applying a powder metallurgical approach. After graphene exfoliation and mechanical mixing, powders were disc milled, compacted and extruded into round rods. Two different sources of commercial graphene nano platelets (GNP) (by 1. Sigma Aldrich (SA) and 2. Alfa Aesar (AA)) were investigated with the main difference being their specific surface area. One subject of the study was to investigate the effect of disc milling processing on the mechanical properties of Al/GNP composites. Results indicated that micro hardness as well tensile yield strength (TYS) and ultimate tensile strength (UTS) were not improved significantly or only slightly when SA-GNPs and a disc milling duration of 1min were applied. Varying the extrusion ratio from R=9:1 to R=14:1 and R=31:1 as well as applying conic or flat face dies for extrusion did not have a significant effect on the mechanical properties. But when disc milling duration is extended to 5min, significantly increased micro hardness (up to 30%), TYS (up to 17%) and UTS (up to 26%) were observed. Application of AA-GNPs as a second source of commercial GNPs also resulted in significantly increased micro hardness (up to 49%), increased TYS (up to 16%) and UTS (up to 27%) when disc milling of 5min is conducted in the powder processing stage. SEM analysis indicated that after 5min disc milling aluminum particles were deformed from spherical into a plate-like shape. Additionally, GNP exfoliation and its dispersion in the Al matrix seemed to be improved by the longer milling duration and could be a reason for the enhanced strengthening effect of GNPs.
Critical comparison of different techniques for producing profiled wires
Authors: KWIECIEŃ M.
Published: April 2023

Abstract. Profiled wires manufactured by the drawing and rolling processes are widely used for production of industrial screens used in the particles separation processes. The main goals in the production processes of such screens are to obtain increased durability and surface quality due to its demanding working environment i.e. high abrasive wear and aggressive condition. The present studies were focused on the analysis of the effects of applied wire drawing and rolling processes on the mechanical properties and surface quality of the produced profile wires. The differences in the schedules of the metal forming processes as well as in the deformation inhomogeneities in the drawn products were analysed. As a result of the applied deformation methods, different surface quality and mechanical properties were obtained. The rolling process has been shown to provide better surface quality and a lower YS/TS ratio, which is critical for further deformations such as the bending process of round industrial screens. The investigations were preformed using austenitic stainless steel.
Design of a forging process to individually examine thermal, mechanical and tribological stress in the tool surface zone
Authors: Behrens B.A.
Published: April 2023

Abstract. The surface layer of hot forging tools undergoes local microstructural changes due to high thermo-mechanical and tribological loads. Tools made of hot working steel are usually pre-heated and experience extreme heating and cooling during each forging cycle, affecting their local wear behaviour significantly. Therefore, the analysis of these tool surface layers in die forging and their effect on wear behaviour is of great importance. The microstructural changes in the tool surface layer mainly depend on thermal loads, which are highly influenced by the tool cooling system. A process and a suitable tool system are developed to vary the thermal and mechanical loads on the tool surface layer and fundamentally examine the resulting microstructural changes.
Effect of near beta-transus forging parameters on the mechanical and microstructural properties of Ti-6Al-4V – Application to hammer forging
Authors: AGIRRE J.
Published: April 2023

Abstract. Ti-6Al-4V is a widely employed material in the aerospace, power generation and bioengineering industries due to its low density, excellent corrosion resistance and outstanding mechanical properties. Hammer forging is one of the most utilized manufacturing processes to produce high-performance titanium components and it is known that the process parameters highly affect the microstructure, and thus, the mechanical properties of the manufactured parts. Ti-6Al-4V alloy has a temperature dependent dual structure and forging below or above the β-transus transition temperature (≈980ºC) highly influences the resultant microstructure. Due to the significant adiabatic heating in high-speed hammer forging processes the β-transus temperature can be exceeded during the process. Therefore, it is of vital importance to study the phase transformation limits and the resultant effects on the mechanical properties to establish the optimum processing window for the hammer forging of Ti-6Al-4V. In this work, the Direct-Impact Drop Hammer (DIDH), a purpose-built laboratory hammer with a maximum blow speed of 5 m/s is employed to perform intermediate strain rate (≈200 s-1) uniaxial compression tests of Ti-6Al-4V at 900ºC, 940ºC, 980ºC, 1000ºC and 1020ºC. The flow behaviour of this titanium alloy is experimentally characterized under a wide range of hammer forging conditions, and the microstructure of the tested samples is analysed to study the influence of the adiabatic heating on the phase transformation of Ti-6Al-4V.
Total strain on the outer surface of steel sheets in air bending
Authors: POKKA A-.P.
Published: April 2023

Abstract. Air bending is a commonly used method for sheet-metal forming. However, several challenges exist around the bending behavior of materials with poor global formability, that are difficult to study using conventional bending test methods, and thus may not be fully understood. In this study, nine thermomechanically rolled steel grades with various strengths and ductility properties are bent using three different punch radii. The strain distributions on the outer surface are measured using Digital Image Correlation (DIC). The relationships between the strain distribution, peak strain, and total strain (area under the strain distribution curve) are determined. The total strain is observed to be independent from the peak strain and the shape of the strain distribution. The total strain is found to depend on the bend angle and sheet thickness. An analytical formula for approximating the total strain is derived. Potential for further approximations of the total strain, strain distribution and bend shape are discussed.
Prediction of forming limit diagram of automotive sheet metals using a new necking criterion
Authors: PHAM Q.T.
Published: April 2023

Abstract. A theoretical model for predicting the forming limit diagram of sheet metal, named MMFC2, was recently proposed by the authors based on the modified maximum force criterion (MMFC). This study examines the application of MMFC2 for two automotive sheets, DP800 and AA6016, which are widely used in making car body parts. Uniaxial tensile and bulge tests are conducted to calibrate constitutive equations for modeling the tested materials. The developed material models are employed into different frameworks such as MMFC, MMFC2, and Marciniak-Kuczynski (MK) models to forecast the forming limit curve (FLC) of the tested materials. Their predictions are validated by comparing with an experimental one obtained from a series of Nakajima tests. It is found that the derived results of MMFC2 are comparable to that of MK model and agreed reasonably with experimental data. Less computational time is the major advantage of MMFC2 against the MK model.
Anisotropic deformation behavior during cup drawing at room temperature of a ZX10 magnesium alloy sheet
Authors: Hama T.
Published: April 2023

Abstract. Magnesium (Mg) alloy sheets have low density and high specific strength; thus, they are expected to facilitate weight reduction of structural components. However, because of the strong crystal anisotropy of the hexagonal structure and the strong basal texture observed in typical rolled Mg alloy sheets, their press formability at room temperature is low. To improve the room-temperature press formability, ZX series Mg alloy sheets that weakened the basal texture have recently been developed. The plastic deformation behavior of a rolled Mg-1.5mass%Zn-0.1mass%Ca (ZX10Mg) alloy sheet was studied in a previous study [7], and it was reported that the plastic deformation behavior showed strong in-plane anisotropy and differed notably from that of AZ series rolled Mg alloy sheets. In the present study, cylindrical cup drawing of a ZX10Mg alloy sheet was performed at room temperature and the drawability was examined in terms of cup height distributions, strain evolution, and texture evolution. The cup height differed significantly between the rolling and transverse directions. The thickness at the cup edge was the largest in the rolling direction and the smallest in the transverse direction. The magnitude relationship of the thickness correlated with the Lankford values under compression. The mechanism that yielded the difference in texture evolution was also discussed.
Improved failure characterisation of high-strength steel using a butterfly test rig with rotation control
Authors: STOCKBURGER E.
Published: April 2023

Abstract. A forming limit diagram is the standard method to describe the forming capacity of sheet materials. It predicts failure due to necking by limiting major and minor strains. For failure due to fracture, the fracture forming limit diagram is used, but fracture caused by plastic deformation at a shear-dominated stress state cannot be predicted with a conventional fracture forming limit diagram. Therefore, stress-based failure models are used as an alternative. These models are describing the fracture of sheet materials based on the failure strain and the stress state. Material-specific parameters must be determined, but a standardised procedure for the calibration of stress-based failure models is currently not established. Most test procedures show non-constant stress paths and varying stress states in the crack initiation area, which leads to uncertainties and inaccuracies for modelling. Therefore, a new test methodology was invented at the IFUM: a prior presented butterfly test rig was extended to enable an online rotation to adapt the loading angle while testing. First, butterfly tests with CP800 were performed for three fixed loading conditions. The tests were modelled numerically with boundary conditions corresponding to the tests. Based on the numerical results, the stress state as well as failure strain were identified and the stress state deviations were calculated. Afterwards, the necessary angular displacements to compensate the stress state deviations for the adaptive test rig were iteratively determined with numerical simulations using an automatised Python script. Finally, the butterfly tests were performed experimentally with the determined adaptive loading angles to identify the specimen failure and compared to the simulations for validation.
Experimental identification of uncoupled ductile damage models and application in flow forming of IN718
Authors: VURAL V.
Published: April 2023

Abstract. The aim of this study is to calibrate the parameters of the Johnson-Cook (JC) and modified Mohr-Coulomb (MMC) ductile failure models for Inconel 718 and predict the formability limit in the flow forming process using the aforementioned uncoupled damage models. Uniaxial tensile tests are performed on four different specimen geometries to cover a variety of stress states. A hybrid methodology combining finite element simulations and experimental findings is used to calibrate the JC and MMC damage models. The models are implemented in the finite element solver Abaqus using a user-defined subroutine. Results show that the calibrated models agree well with the experimental data in all tensile tests. In shear dominant loads, the MMC model is found to be more capable of showing accurate crack propagation. In flow forming simulations, a significant difference is observed between the JC and MMC models in the prediction of damage. Lode parameter-dependent damage models, such as the MMC, are found to be more suitable for the prediction forming limits in the flow forming process.
Influence of intercritical annealing temperature on formability and mechanical properties of medium-manganese-steel in press hardening
Authors: TILLY K.J.
Published: April 2023

Abstract. Ultra-high-strength-steel parts produced by press hardening are widely used in the automotive sector for lightweight construction and passenger safety applications. Medium-manganese-steels (MMnS) are currently investigated as an alternative to boron-manganese steels. Their favorable mechanical properties of high strength and high ductility after quenching are often based on rather complex heat treatment strategies resulting in a multiphase microstructure. One possible way such a microstructure can be obtained, is intercritical annealing and subsequent quenching during the press hardening process. For this processing route formability during hot stamping and final properties of the quenched material are dependent on the annealing temperature. For a successful part production, an annealing temperature that satisfies both, in-process properties, as well as final mechanical properties is mandatory. In this paper, the suitability of the intercritical annealing process route for press hardening of MMnS is investigated for a specific MMnS alloy. Formability in hot stamping conditions with respect to different annealing temperatures (range 700°C – 800°C) are examined by performing hot tensile tests, as well as experimental trials using a hot stamping tool. Final properties are analyzed by tensile tests. The formability during hot tensile tests and hot stamping show a strong positive correlation to the annealing temperature, while the values for uniform and ultimate elongation of the quenched material shows a strong negative correlation to the annealing temperature. The tensile strength of the quenched material shows a low sensitivity to the annealing temperature. No annealing temperature that satisfies both, in-process and final properties, could be found for the investigated MMnS alloy.
Effect of prestrain on mechanical behavior of aluminum alloys
Authors: VINCZE G.
Published: April 2023

Abstract. Sheet metal forming involves many times large plastic strain and strain path changes. It is well known that the plastic behavior of metals is strain path sensitive. In monotonic loading, the microstructure as well as the crystallographic texture evolve during deformation leading usually to a gradual material hardening that tends to saturate at large strains. Such evolution can be interrupted if a severe change of strain path occurs. The simplest way to change drastically the strain path is through reverse loading, namely, by loading the material in opposite direction to the previous one. In this case, the material behavior can show one or more characteristics, such as the Bauschinger effect, transient hardening, softening or hardening. This work investigated the effects of the prestrain on the mechanical response of the material subjected to reverse simple shear. The prestrain is produced by rolling, either symmetric or asymmetric, and different amounts of equivalent strain. Three routes of rolling are used, namely, symmetric, asymmetric continuous, and asymmetric reverse [1]. The Bauschinger effect slightly decreases with the prestrain increase for the initial material. After rolling, the Bauschinger effect is insensitive to the rolling route, and it is also insensitive to the amount of the rolling prestrain.
The effectiveness of e-book in learning process
Authors: Suriani Ni Made , Agustini Ketut , Sudhata I Gde Wawan , Dantes Gede Rasben
Published: April 2023

This study aims to analyze the effectiveness of e-books in the last three years and to analyze what types of e-books are most appropriate for current learning. The methodology used is based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). Articles related to the use of e-books from 2020-2022 were searched through the published or perish article search application that focuses on Scopus-indexed articles. The results obtained indicate that the existence of e-books is still widely used to support students to obtain even better learning outcomes. Although several studies have found no significant difference between the use of e-books and regular printed books, the results also show that e-book users got higher learning outcomes. For now, the use of interactive e-books is the most effective e-book of other types, considering that this type of e-book has been tested on users of various ages and different educational backgrounds, with different subjects and different places of implementation.
Rostros y rastros de investigación: el aporte de la investigadora Fulvia García Roa a la innovación en el sector agropecuario colombiano. Edición especial dedicada al control biológico
Authors: García Roa Fulvia , Rojas Álvarez Liliana , Kondo Takumasa , Cañar Serna Dubert Yamil , Tibaduiza Castañeda Leidy Patricia
Published: April 2023

Este libro es la continuación de una propuesta que indaga la manera de aportar a la innovación desde los procesos de crecimiento profesional de investigadores del sector agropecuario colombiano. Esto generó una bella oportunidad de dimensionar el aporte de una mujer, científica y pionera a la investigación, cuya pasión y trayectoria constituyen un importante hito corporativo. Realizar esta obra en meses previos a su fallecimiento nos permitió tener la oportunidad, a quienes contribuimos como coautores, de dar testimonio de una mujer sencilla y amorosa; entregada a su trabajo y a su familia; convencida de la necesidad de compartir su esfuerzo por contribuir al agro no solo desde la perspectiva del control biológico, sino también desde la insistencia en cocrear conocimiento con el productor y en el relacionamiento como pilar de las soluciones basadas en ciencia y tecnología. Esperamos que con esta publicación se cumpla su deseo de compartir parte de su esfuerzo, honrar a su familia y motivar a niñas, mujeres y, en general, a las nuevas generaciones a transitar los caminos de la ciencia, la tecnología y la innovación en el agro colombiano.
Sensa Mobile App for Managing Stress, Anxiety, and Depression Symptoms: Pilot Cohort Study
Authors: Valinskas Sarunas , Nakrys Marius , Aleknavicius Kasparas , Jonusas Justinas
Published: April 2023

Background

An increase in depression, anxiety, and stress symptoms worldwide, attributed to the COVID-19 pandemic, has been reported. If not treated, it may negatively affect a person's everyday life by altering physical and social well-being and productivity and increasing expenditure on health care. Cognitive behavioral therapy (CBT)–based interventions are gaining popularity as a means to reduce stress and alleviate anxiety and depression symptoms. Moreover, CBT delivered through a mobile app has the same elements as traditional CBT training (eg, guided discovery). However, unlike conventional training, users of mobile apps are allowed to tailor their own experience at their own speed and schedule.

Objective

This study aims to analyze Sensa users’ retrospective data and explore the dose-duration effect to find the optimal usage time when the user showed results.

Methods

The study cohort comprised 381 consecutive community-based nonclinical users who started using Sensa between October 2021 and March 2022. All users included in the study took the Depression Anxiety Stress Scale-21 (DASS-21) assessment at least 2 times. Other parameters from the database containing all self-reported data were gender, number of active days, total time of use, and age. The primary outcome of the study was a change in the DASS-21 score. Statistical analyses were performed using GraphPad Prism (version 9, GraphPad Software). In addition, a logistic regression model was created to predict how the obtained independent parameters influenced the DASS-21 score.

Results

The main finding of our study was that the majority of participants who started using Sensa were experiencing depression, anxiety, and stress symptoms (92.13%, 80.05%, and 87.93%, respectively). There was a statistically significant decrease of the DASS-21 subdomain scores after the use of the application (anxiety: mean 7.25, SD 4.03 vs mean 6.12, SD 4.00; P=.001; depression: mean 11.05, SD 4.26 vs mean 9.01, SD 4.77; P=.001; stress: mean 11.42, SD 3.44 vs mean 9.96, SD 3.65; P<.001). Finally, the logistic regression model showed that users who were using the app for more than 24 days and had at least 12 active days during that time had 3.463 (95% CI 1.142-11.93) and 2.644 (95% CI 1.024-7.127) times higher chances to reduce their DASS-21 subdomain scores of depression and anxiety, respectively.

Conclusions

Using the Sensa mobile app was related to decreased depression, anxiety, and stress symptoms.
A Novel Capacity-Strengthening Intervention for Frontline Harm Reduction Workers to Support Pre-exposure Prophylaxis Awareness-Building and Promotion Among People Who Use Drugs: Formative Research and Intervention Development (Preprint)
Authors: Glick Jennifer L , Zhang Leanne , Rosen Joseph G , Yaroshevich Karla , Atiba Bakari , Pelaez Danielle , Park Ju Nyeong
Published: April 2023

BACKGROUND

HIV prevalence among people who use drugs (PWUD) in Baltimore, Maryland, is higher than among the general population. Pre-exposure prophylaxis (PrEP) is a widely available medication that prevents HIV transmission, yet its usefulness is low among PWUD in Baltimore City and the United States. Community-level interventions to promote PrEP uptake and adherence among PWUD are limited.

OBJECTIVE

We describe the development of a capacity-strengthening intervention designed for frontline harm reduction workers (FHRWs) to support PrEP awareness-building and promotion among PWUD.

METHODS

Our study was implemented in 2 phases in Baltimore City, Maryland. The formative phase focused on a qualitative exploration of the PrEP implementation environment, as well as facilitators and barriers to PrEP willingness and uptake, among cisgender women who use drugs. This work, as well as the existing literature, theory, and feedback from our community partners, informed the intervention development phase, which used an academic-community partnership model. The intervention involved a 1-time, 2-hour training with FHRWs aimed at increasing general PrEP knowledge and developing self-efficacy promoting PrEP in practice (eg, facilitating PrEP dialogues with clients, supporting client advancement along a model of PrEP readiness, and referring clients to PrEP services). In a separate paper, we describe the conduct and results of a mixed methods evaluation to assess changes in PrEP-related knowledge, attitudes, self-efficacy, and promotion practices among FHRWs participating in the training.

RESULTS

The pilot was developed from October to December 2021 and implemented from December 2021 through April 2022. We leveraged existing relationships with community-based harm reduction organizations to recruit FHRWs into the intervention. A total of 39 FHRWs from 4 community-based organizations participated in the training across 4 sessions (1 in-person, 2 online synchronous, and 1 online asynchronous). FHRW training attendees represented a diverse range of work cadres, including peer workers, case managers, and organizational administrators.

CONCLUSIONS

This intervention could prevent the HIV burden among PWUD by leveraging the relationships that FHRWs have with PWUD and by supporting advancement along the PrEP continuum. Given suboptimal PrEP uptake among PWUD and the limited number of interventions designed to address this gap, our intervention offers an innovative approach to a burgeoning public health problem. If effective, our intervention has the potential to be further developed and scaled up to increase PrEP awareness and uptake among PWUD worldwide.