Maximum Distortion Research Articles

Distortion prediction and geometry compensation using modified inherent strain method for additively manufactured Ti-6Al-4V

A laser powder bed fusion (LPBF) process enables the production of intricate geometries for specialized applications demanding high precision in various industries such as medical, aerospace, and automotive. However, substantial thermal gradients in the LPBF process often led to residual stress, resulting in noticeable distortion and potential part failure of fabricated parts. Therefore, the present work investigates distortion prediction and geometry compensation for additively manufactured Ti-6Al-4V components employing a modified inherent strain method. Unlike previous studies, both relaxed distortions from substrate removal and as-built distortion are considered, incorporating specimens with varying geometrical features such as height and thickness. The study aims to comprehensively evaluate the efficacy of the modified inherent strain approach in capturing distortion under different build scenarios and assess the effectiveness of geometrical compensation in minimizing as-built distortion. Overall, we found that numerical models effectively capture relaxed deflection for samples with varied geometrical features, showing reasonable agreement with experimental results. Additionally, the as-built distortion of samples with thicknesses of 5 mm and above is well-predicted, with an average deviation between numerical and experimental results of approximately 0.125 mm. Nonetheless, we noted the challenge in capturing out-of-plane distortion for thin wedges, suggesting avenues for future investigation. Furthermore, geometry compensation reduces maximum distortion from 0.68 to 0.28 mm and average distortion from 0.15 to 0.05 mm. Multiple iterations of compensation yield insignificant differences in distortion reduction, which suggests sufficient distortion alleviation from single compensation for geometries explored in the present work. Overall, the study provides valuable insights into distortion prediction and compensation strategies for additively manufactured Ti-6Al-4V components.

Experimental and simulation studies to optimize the mechanical alloying process of ODS-FeCrAl alloy powder

Oxide dispersion strengthened (ODS) FeCrAl alloy exhibits superior mechanical qualities at high temperatures and resistance to neutron irradiation, making it a highly promising material for accident-tolerant fuel cladding. The preparation of ODS-FeCrAl alloy powder by mechanical alloying can mix Y2O3 and FeCrAl alloy powder uniformly and promote the uniform dispersion of nanoscale oxide particles in the alloy matrix. The preparation of ODS-FeCrAl alloy powder by the mechanical alloying method is greatly influenced by the rotational speed. Therefore, this study uses a combination of experiments and numerical simulation to investigate the effects of different rotational speeds on the microscopic morphology, particle size and force of alloy powder during the ball milling process. The mechanically alloyed powder was subjected to XRD inspection to determine the optimum ball milling time at each rotational speed by means of the maximum lattice distortion, and then the powder micromorphology and particle size were analyzed. Then the forces on the powder and grinding ball during the ball milling process were analyzed by numerical simulation, and it was found that the collision force and normal force played a dominant role in the ball milling process. The combined experimental and simulation results determined that the ODS-FeCrAl alloy powder obtained by ball milling at 300 rpm for 35 h had the largest lattice distortion, fine grain size and uniform particle size, which achieved the best mechanical alloying effect.

Experimental investigation of the aerodynamics of a UAV inlet with double 90° bends

Unmanned aerial vehicle (UAV) inlets commonly have a compact S-shaped inlet structure for the sake of stealth. Most of the current studies on subsonic inlets have focused on S-shaped configurations with relatively gentle transitions of the flow channel. In this study, the aerodynamic performance and swirl flow characteristics of a UAV inlet, which has double 90° bends in the duct and is integrated with an aircraft fuselage and a volute, are studied both experimentally and numerically. The influences of angle of attack, sideslip angle, AIP (Aerodynamic Interface Plane) Mach number, and freestream airspeed are analyzed. A measure of adding two deflectors in front of the first bend and a baffle at the bottom of the volute is proposed to improve the total pressure distortion and swirl distortion characteristics of the inlet. Finally, a practice of shape optimization is performed to further improve the aerodynamic performance and swirl flow characteristics on the basis of the baseline configuration. The results indicate that the maximum and minimum total pressure recovery coefficients of the baseline inlet configuration are 0.982 and 0.969, respectively, as well as the maximum total pressure distortion index of –0.0814 and the maximum swirl distortion index of 32.1 % under normal operating conditions. Through a total of 8 iterations of optimization, the total pressure recovery coefficient is eventually improved by 0.21 % of that of the baseline configuration, as well as the total pressure distortion index, swirl distortion index and maximum swirl angle reduced by 43.6 %, 4.6 % and 11.1 %, respectively.

Cross-section distortion and springback characteristics of double-cavity aluminum profile in force controlled stretch-bending

A 3D elastic-plastic FE model for simulating the force controlled stretch-bending process of double-cavity aluminum profile was established using hybrid explicit−implicit solvent method. Considering the computational accuracy and efficiency, the optimal choices of numerical parameters and algorithms in FE modelling were determined. The formation mechanisms of cross-section distortion and springback were revealed. The effects of pre-stretching, post-stretching, friction, and the addition of internal fillers on forming quality were investigated. The results show that the stress state of profile in stretch-bending is uniaxial with only a circumferential stress. The stress distribution along the length direction of profile is non-uniform and the maximum tensile stress is located at a certain distance away from the center of profile. As aluminum profile is gradually attached to bending die, the distribution characteristic of cross-section distortion along the length direction of profile changes from V-shape to W-shape. After unloading the forming tools, cross-section distortion decreases obviously due to the stress relaxation, with a maximum distortion difference of 13% before and after unloading. As pre-stretching and post-stretching forces increase, cross-section distortion increases gradually, while springback first decreases and then remains unchanged. With increasing friction between bending die and profile, cross-section distortion slightly decreases, while springback increases. Cross-section distortion decreases by 83% with adding PVC fillers into the cavities of profile, while springback increases by 192.2%.

Radiation Pattern Correction of Faulty Planar Phased Array using Genetic Algorithm

The probability of antenna array failure or malfunctioning cannot be ruled out, and hardware replacement of faulty elements is not always a viable solution. Therefore, academic and industrial interest in self-healing phased arrays are on the rise. In this work, the phase-only genetic algorithm (GA) optimization flow for the radiation pattern correction of a 4 × 4 phase faulty planar antenna array is proposed. Initially, a reference array pattern at the desired scan angle is generated. Then random phase faults are introduced across the 1 × 4 antenna elements in any one of 4 sub-arrays to produce maximum distortion in the reference radiation pattern of 4 × 4 planar array. The proposed GA re-computes the new excitation weights for the remaining non-faulty 3 sub-arrays to correct the overall radiation pattern of 4 × 4 array. This is achieved by calculating the array output power for reference and GA computed weights. The GA corrected patterns fairly follow the desired array patterns in terms of peak gain and reducing sidelobe levels for the desired scan angle. The efficiency of the optimized radiation patterns was evaluated in full-wave HFSS model and measurements validation. In this way, maintenance cost can be reduced with recovery of acceptable level of radiation pattern using software instead of physically replacing faulty antenna elements in the array.

Pre- and in-process dimensional compensation in the selective thermoplastic electrophotographic process

As a cutting-edge additive manufacturing (AM) technology, the selective thermoplastic electrophotographic process (STEP) has opened up possibilities for mass production with its combination of real engineering plastics and potential high part quality. To improve the accuracy and fidelity of STEP for the most demanding applications, this paper proposes a novel method encompassing both pre-processing and in-process dimensional compensations. Iterative compensation before production is achieved through physics-driven simulation, resulting in input masks that better match the required dimensions at the design level. Layer-wise compensation is implemented during the production process through the laser profiler system, thereby suppressing the accumulation of surface unevenness during printing. With the compensation method proposed in this paper, the maximum distortion during simulated printing is decreased by 86.2%, and surface unevenness is effectively controlled during the printing process.

Residual strength assessment of a heat straightened ASTM A 7 Steel I-section member exposed to a fire event

Heat straightening is an efficient and cost-effective method of repairing steel members that have experienced impact or fire-induced deformations. Postfire investigations have shown that fire exposure can cause considerable loss of residual mechanical properties. Beyond the fire event itself, additional heat applied to the member during the straightening process can, potentially, even further modify the mechanical properties of steels. This study aims to evaluate residual mechanical behavior at zones of maximum heat-induced distortion representative of both the fire event and the heat-straightening repair of a fire-damaged steel I-section. The study further aims to independently observe heating patterns, working temperatures, and external jacking forces during heat straightening. The fire-damaged member was restrained in three-point bending with fork boundary conditions simulating service conditions for a discretely braced bridge stringer. Results revealed that the cumulative effect of both the fire and the repair caused measurable differences in mechanical properties compared with an undamaged portion of the member, but mean properties still exceeded ASTM International’s ASTM A 7 product and the AASHTO nonfracture-critical toughness requirements. Supplemental metallographic analyses revealed no measurable alteration in metallurgical phase composition or grain size of the steel, indicating that heat straightening would have been a viable repair solution to keep the member in service.

Crack Initiation and Propagation Mechanism of Flawed Rock Mass Based on Improved Maximum Distortion Energy Theory and PFC Numerical Simulation

Crack Initiation and Propagation Mechanism of Flawed Rock Mass Based on Improved Maximum Distortion Energy Theory and PFC Numerical Simulation

Data-driven distortion compensation for laser powder bed fusion process using Gaussian process regression and inherent strain method

The repeated melting and solidification cycles in the laser powder bed fusion (L-PBF) process lead to significant thermal gradients, resulting in notable distortion in the as-built part. Distortion compensation methods, which pre-deform the part design so the as-built shape aligns with the target, have been widely adopted to mitigate this issue. This research introduces a data-driven distortion compensation framework for the L-PBF process. It employs an experimentally-calibrated inherent strain method to generate a dataset and utilizes Gaussian process regression to create the compensated geometry. Experimental validation shows that the proposed method can reduce the maximum distortion by up to 82.5% for a lattice structure and 77.8% for a canonical part. Furthermore, the compensation results reveal that (1) the lumped layer thickness in finite element models has little impact on simulated distortion reduction but can notably affect the experimental reduction; (2) discrepancies between simulated and experimental compensation performance are largely attributed to the curvy surfaces with sharp transitions in trial and compensated shapes, a result of pre-deforming the design; (3) the number of trial geometries considerably affects the effectiveness of compensation, while the number of deformation states does not have a statistically significant impact.

Design for a virtual reality head-mounted display with holographic pancake optics

A design for a head-mounted display using holographic optical elements (HOEs) and pancake optics is presented. The pancake optics assembly consists of a circular polarization, quarter-wave film, and a coated 50/50 (semi-transmissive and semi-reflective) aspherical lens. The HOE and pancake optics combination was employed to reduce the volume of the system. For this design, the effective focal length was 10.901 mm, the field of view was 30 deg, and the f-number was 3.633. In terms of image quality, the modulation transfer function (MTF) values for all fields exceeded 0.3 at 65 lp/mm. The MTF values for all fields under the tolerance error also exceeded 0.3 lp/mm. The maximum optical distortion was less than 2%. The impact of the efficiency of diffracted and non-diffracted light on the visibility was analyzed to select the appropriate reflectance for the coating of the 50/50 aspherical lens and the highest hologram diffraction efficiency to achieve the best visibility.

Synergistic design strategy for enhancing the piezoelectric performance of BiFeO3-Based high-temperature piezoelectric ceramics

A novel synergistic strategy was used to improve the piezoelectric characteristics of high-temperature piezoelectric ceramics. This work combined three commonly used strategies, constructing the Morphotropic Phase Boundary to reduce energy barriers, changing domain structures impacting macroscopic piezoelectric properties, and adjusting BO6 octahedral distortions reflecting microstructural changes, thus effectively regulating the piezoelectric behaviors of BiFeO3-based ceramics. As a result, the 0.67BiFeO3-0.32BaTiO3-0.01BiAlO3 component, exhibiting the maximum distortion of the BO6 octahedron and the coexistence of macrodomains and nanodomains, achieved the optimal piezoelectric characteristics (d33 = 225 ± 10 pC N−1, TC = 450 °C). Additionally, the ceramic maintained its high piezoelectric properties even at temperatures as high as 280 °C (346 pC N−1). This study presents a novel collaborative design strategy that combines phase structure, domain structure, and BO6 octahedral distortion, significantly enhancing the development potential of lead-free high-temperature piezoelectric materials in the future.

Experiment and FEA simulation for predicting maximum distortion in the submerged arc welding process

Experiment and FEA simulation for predicting maximum distortion in the submerged arc welding process

Optical system design of a femi-class ultra-high-resolution spectrometer based on the quaternary dispersion of a middle echelon grating

In order to meet the needs of the femi-ultra-high spectral resolution test, an optical system of the femi-ultra-high spectral resolution spectrometer in the spectral range of 190–800 nm is designed based on the quaternary dispersion of the middle echelon grating under the condition that the volume and weight of the spectrometer do not increase sharply. After the optimization design, the spectral resolution can reach 51.149 fm in the full field of view of 0.5 mm; at the wavelength of 191 nm, the spectral resolution in the whole spectral range is better than 150 fm, and the maximum distortion of the system is 0.2288%, which can provide a feasible reference for the subsequent design of the spectrometer optical system to realize the simultaneous detection of a wide band and high spectral resolution.

Assessing the efficiency of measures to enhance electric power quality in variable-frequency drive for scraper conveyors

The intensive implementation of variable-frequency drive machines and installations in underground mining processes necessitates addressing several issues, with a primary focus on ensuring the quality of electric power. Elevating the energy resource of mining machines and enhancing the energy efficiency of mining operations requires maintaining the rated indicators of electric power quality in mine power distribution systems. Achieving this involves assessing the level and composition of higher harmonic components in voltage and current within power circuits equipped with variable-frequency drives (VFD). Key objectives encompass the development of a simulation model based on the equivalent diagram of the power distribution system substitution with a scraper conveyor VFD to scrutinize the spectral composition of higher harmonic components in the power circuits of the mine power distribution system (MPDS). Additionally, the study involves analyzing the impact of harmonic filters (HFs), reactors, and sine filters on the quality of electric power in the VFD system of a scraper conveyor. Further analysis extends to the spectral composition of higher harmonic components in circuits related to insulation leakage and metering circuits of the residual-current device. Practical recommendations for improving electric power quality in the VFD system of a scraper conveyor are then developed based on the research findings. The established model of a variable-frequency drive system for scraper conveyors facilitates the assessment of the effectiveness of electric power quality improvement measures. The harmonic composition of voltage and current in the mine power distribution system is determined under maximum distortion conditions and in the presence of HFs, reactors, and sine filters. Research methods are chosen to unveil the spectral composition of voltage and current in symmetrical and single-phase modes of insulation leakage, as well as in metering circuits of residual-current devices (RCDs). It is noted that the harmonic composition of leakage voltage and current is primarily influenced by the parameters of the output voltage modulated by the autonomous frequency converter inverter. Considering the high level of harmonic components in voltage and current, adjustments to RCD settings, capacitive current compensator, and the protective shunting unit are recommended for electrical safety. The study emphasizes the importance of scientifically substantiating the rated indicators of higher harmonic components for leakage circuits and further exploring the physiological effects of higher current harmonics on the human body. The feasibility of installing a harmonic filter (HF) directly on the low-voltage supply section of a scraper conveyor should be technically justified. Interestingly, the presence of HFs, reactors, and sine filters does not significantly impact the harmonic composition or the magnitudes of coefficients of the harmonic components in the phase voltage of the system concerning ground and leakage currents through insulation. However, higher harmonic components induced in leakage current circuits may pose a potential hazard, leading to a violation of magnetic compatibility and posing risks in case of contact with live parts of electrical equipment.

Validation of echo planar imaging based diffusion-weighted magnetic resonance imaging on a 0.35 T MR-Linac

Background and PurposeThe feasibility of acquiring diffusion-weighted imaging (DWI) images on an MR-Linac for quantitative response assessment during radiotherapy was explored. DWI data obtained with a Spin Echo Echo Planar Imaging sequence adapted for a 0.35 T MR-Linac were examined and compared with DWI data from a conventional 3 T scanner. Materials and MethodsApparent diffusion coefficient (ADC) measurements and a distortion correction technique were investigated using DWI-calibrated phantoms and in the brains of seven volunteers. All DWI utilized two phase-encoding directions for distortion correction and off-resonance field estimation. ADC maps in the brain were analyzed for automatically segmented normal tissues. ResultsPhantom ADC measurements on the MR-Linac were within a 3 % margin of those recorded by the 3 T scanner. The maximum distortion observed in the phantom was 2.0 mm prior to correction and 1.1 mm post-correction on the MR-Linac, compared to 6.0 mm before correction and 3.6 mm after correction at 3 T. In vivo, the average ADC values for gray and white matter exhibited variations of 14 % and 4 %, respectively, for different selections of b-values on the MR-Linac. Distortions in brain images before correction, estimated through the off-resonance field, reached 2.7 mm on the MR-Linac and 12 mm at 3 T. ConclusionAccurate ADC measurements are achievable on a 0.35 T MR-Linac, both in phantom and in vivo. The selection of b-values significantly influences ADC values in vivo. DWI on the MR-Linac demonstrated lower distortion levels, with a maximum distortion reduced to 1.1 mm after correction.

Dynamic Projection Method of Electronic Navigational Charts for Polar Navigation

Electronic navigational charts (ENCs) are geospatial databases compiled in strict accordance with the technical specifications of the International Hydrographic Organization (IHO). Electronic Chart Display and Information System (ECDIS) is a Geographic Information System (GIS) operated by ENCs for real-time navigation at sea, which is one of the key technologies for intelligent ships to realize autonomous navigation, intelligent decision-making, and other functions. Facing the urgent demand for high-precision and real-time nautical chart products for polar navigation under the new situation, the projection of ENCs for polar navigation is systematically analyzed in this paper. Based on the theory of complex functions, we derive direct transformations of Mercator projection, polar Gauss-Krüger projection, and polar stereographic projection. A rational set of dynamic projection options oriented towards polar navigation is proposed with reference to existing specifications for the compilation of the ENCs. From the perspective of nautical users, rather than the GIS expert or professional cartographer, an ENCs visualization idea based on multithread-double buffering is integrated into Polar Region Electronic Navigational Charts software, which effectively solves the problem of large projection distortion in polar navigation applications. Taking the CGCS2000 reference ellipsoid as an example, the numerical analysis shows that the length distortion of the Mercator projection is less than 10% in the region up to 74°, but it is more than 80% at very high latitudes. The maximum distortion of the polar Gauss-Krüger projection does not exceed 10%. The degree of distortion of the polar stereographic projection is less than 1% above 79°. In addition, the computational errors of the direct conversion formulas do not exceed 10−9 m throughout the Arctic range. From the point of view of the computational efficiency of the direct conversion model, it takes no more than 0.1 s to compute nearly 8 million points at 1′×1′ resolution, which fully meets the demand for real-time nautical chart products under information technology conditions.

A numerical investigation of the role of basements on tunnel-frame interaction in sandy soil

This paper investigates the role of basement depth on the response of framed buildings to tunnel construction in sandy soil using finite element modelling. Six frames are considered to explore the influences of tunnel cover depth, building width, eccentricity, and the number of storeys on the role of basement depth. The numerical models adopt the hypoplastic constitute model to simulate the behaviour of the sand. The results suggest that basement depth plays an important role in determining the settlements of the raft foundations and soil displacements due to tunnelling. Its effect on the structural shear distortion primarily depends on the ratio of tunnel depth to building width (C/B); an increase in basement depth decreases and increases building maximum shear distortion for C/B<0.3 and for C/B>0.35, respectively. The basement considerably increases the shear distortion of short eccentric structures by preventing tilt of the building, causing a divergence from existing empirical envelopes and modification factors for shear distortion. The applicability of the meta-model is extended to the embedded structures by linking the building tilt freedom coefficient with the basement depth parameter, achieving good agreement between the predicted results and calculated data. Limitations and practical implications of the research are briefly discussed.

Influence of build orientation and support structure on additive manufacturing of human knee replacements: a computational study.

Developing patient-specific implants has an increasing interest in the application of emerging additive manufacturing (AM) technologies. On the other hand, despite advances in total knee replacement (TKR), studies suggest that up to 20% of patients with elective TKR are dissatisfied with the outcome. By creating 3D objects from digital models, AM enables the production of patient-specific implants with complex geometries, such as those required for knee replacements. Previous studies have highlighted concerns regarding the risk of residual stresses and shape distortions in AM parts, which could lead to structural failure or other complications. This article presents a computational framework that uses CT images to create patient-specific finite element models for optimizing AM knee replacements. The workflow includes image processing in the open-source software 3DSlicer and MeshLab and AM process simulations in the commercial platform 3DEXPERIENCE. The approach is demonstrated on a distal femur replacement for a 50-year-old male patient from the open-access Natural Knee Data. The results show that build orientations have a significant impact on both shape distortions and residual stresses. Support structures have a marginal effect on residual stresses but strongly influence shape distortions, whereas conical support exhibits a maximum distortion of 18.5 mm. Future research can explore how these factors affect the functionality of AM knee replacements under in-service loading.

Distortions of parabolic mirror optics for stereophonic lithography and prospects of compensations

The distortions of parabolic mirror optics used for stereophonic projection lithography were investigated. It has already been demonstrated that resist patterns are replicable on gently curved surfaces using mirror optics composed of faced paraboloids of revolution. However, it was found that replicated resist patterns were somewhat distorted from the original patterns. The distortions were caused by characteristics of projection optics. For this reason, the distortions were first calculated by tracing light rays. The calculation procedures are explained in detail. The calculated distortions almost coincide with the ones obtained by experiments. Next, the influences of distortions on the distributions of image intensity and replicated pattern widths were investigated. The maximum distortions reached 29% of the original size at the right-side corners of a 12 mm square, and the light intensity was lowered by 30%. For this reason, printed 200 μm pattern widths reached more than 500 μm on the right side. This was considered to be unfavorable for applying the method universally in various uses. For this reason, methods for compensating or modifying the optics distortions were investigated, and light intensity distributions were discussed.

On the modelling of distorted thin-walled stiffened panels via a scale reduction approach for a simplified structural stress analysis

To reduce the weight of cruise ships, the shipbuilding industry is interested in thin-walled superstructures, where the thickness of butt-welded plates in stiffened panels is under 5 mm. Compared to thick plates, thin ones can develop severe welding-induced distortions, which limit the validity of recommended early-design structural stress assessment methods. Therefore, computationally costly 3D non-linear numerical analysis must be used. For a quick and effective early design, this paper investigates on simplified computational models for thin-walled panels under uni-axial tension, considering the distortions measured on 4-mm thick, full-scale ship-deck panels. A 2D simply-supported analytical plate is shown to be sufficiently accurate (i.e., error <10%) at 150MPa for a distortion with maximum slope within 0.02rad and amplitude smaller than the thickness (t). Moreover, a 1D beam numerical analysis efficiently predicts local stresses around the butt weld when the maximum distortion amplitude is below 0.6×tmm. The distortion needs to be considered at least up to a length of half of the plate width from the weld location and can represent longitudinal profiles within 60% of the plate width. In conclusion, the early structural stress assessment of thin-walled panels can be significantly simplified, thus helping bridge the gap between complex numerical analysis and simplified analytical solutions.