Analysis of 3D Plastic Deformation in Vertical Rolling Based on Global Weighted Velocity Field

Energy method is an essential theoretical approach to analyze plastic forming, which is widely used in rolling. An analysis model for vertical rolling process is established according to energy theory. By using global weighted method firstly, the 3D continuous velocity field, strain rate field and the corresponding power functional are proposed. The unknown variables are solved numerically based on the principle of minimum energy. Then, deformation parameters and rolling force are determined. The analysis on specific examples with the width reduction rate of 0.03~0.05 shows that the theoretical prediction value of weighted model is in good agreement with experimental results. Moreover, the effects of several shape and rolling parameters on rolling force, rolling power and edge deformation are studied. Both the width reduction rate and initial slab thickness have significant influences on dog-bone size and rolling force. A wider slab slightly increases the nonuniformity of dog-bone deformation. An increase of vertical roller radius can weaken the edge deformation.

Fabrication and Mechanical Testing of the Uniaxial Graded Auxetic Damper

Auxetic structures can be used as protective sacrificial solutions for impact protection with lightweight and excellent energy-dissipation characteristics. A recently published and patented shock-absorbing system, namely, Uniaxial Graded Auxetic Damper (UGAD), proved its efficiency through comprehensive analytical and computational analyses. However, the authors highlighted the necessity for experimental testing of this new damper. Hence, this paper aimed to fabricate the UGAD using a cost-effective method and determine its load–deformation properties and energy-absorption potential experimentally and computationally. The geometry of the UGAD, fabrication technique, experimental setup, and computational model are presented. A series of dog-bone samples were tested to determine the exact properties of aluminium alloy (AW-5754, T-111). A simplified (elastic, plastic with strain hardening) material model was proposed and validated for use in future computational simulations. Results showed that deformation pattern, progressive collapse, and force–displacement relationships of the manufactured UGAD are in excellent agreement with the computational predictions, thus validating the proposed computational and material models.

A New Specimen Geometry for Evaluation of the Mechanical Orthotropic Properties Presented in Parts Printed by FDM

Additive manufacturing (AM) by FDM (Fused Deposition Modeling) has been increasingly adopted due to the low cost of 3D printers as an option capable of producing parts with complex geometries. Since the FDM process is a layer-by-layer manufacturing method, the characterization of the behavior of parts manufactured by this technology, especially with regard to anisotropic mechanical properties, has led to many works relating printing parameters with tensile strength. However, the use of specimens with the conventional flat "dog bone" and cylindrical geometries specified in the ASTM-638 standards do not perfectly suit the special characteristics of parts produced by FDM, since these standards were created for solid and isotropic materials. A new geometry for specimens printed in FDM to study anisotropy transverse to layer deposition is suggested in this work. Problems such as slippage and crushing in the grips of the test machines due to the fragility of the bound between the beds, as well as the appearance of lateral forces that distort the results due to misalignment of the tensile load, twists and curvature of the specimens, normally observed in the Strain measurements by extensometers, are suppressed with the adoption of the new geometry presented in this work. Keywords: Fused Deposition Modeling, Additive Manufacturing, Mechanical Strength, Tensile Testing, Specimen Geometry

Effect of heat treatment on crystallinity and mechanical properties of flexible structures 3D printed with fused deposition modeling

Fused Deposition Modeling (FDM) is a widely used 3D printing technique, which works based on the principle of melted polymer extrusion through nozzle(s) and depositing them on a build plate layer by layer. However, products manufactured with this method lack proper mechanical strength. In this work, 2/1 twill weave fabric structures are 3D printed using poly (lactic) acid (PLA). The ultimate tensile strength in the warp and weft directions and the modulus (stiffnesses) are measured for non-heat-treated (NHT) samples. The printed samples were heat-treated (HT) to improve the strength and stiffness. The variation in ultimate tensile strength is statistically insignificant in warp direction at all temperatures; however, the tensile strength in weft direction decreased after heat treatment. The modulus in warp direction increased by 31% after heat treatment while in the weft direction it decreased after heat treatment. Differential scanning calorimetry (DSC) tests showed the highest crystallinity at 125°C. The properties of the twill fabrics were compared with a standard dog-bone (DB) specimen using uniaxial tensile tests, Differential scanning calorimetry tests, and optical microscope (OM). For dog-bone specimens, the maximum values of crystallinity, ultimate tensile strength, and modulus were found to be at 125°C. The maximum crystallinity percentages are higher than that of the NHT samples. The ultimate tensile strength of NHT DB specimen 3D printed in horizontal orientation improved after heat treatment. The ultimate tensile strength of DB samples in vertical directions increased after heat treatment as well. The stiffness increased in both directions for DB samples.

Tensile Behaviour of Slag-based Engineered Cementitious Composit

Engineered Cementitious Composites (ECC) have become another alternative in the concrete industry due to their excellent strain capacity under uniaxial tension. Research and development for new ECC mix incorporating wastes remain open to fulfil the industrial needs to produce green and sustainable ECCs. This paper presents the experimental work on the tensile and cracking behaviour of ECCs utilising industrial waste, namely ground granulated blast-furnace slag (GGBS), to replace cement. A total of four slag-based ECC mixes containing 2%–2.5% of PVA fibres and 50%-60% GGBS were investigated under uniaxial compressive and tensile tests. Compressive strength, tensile strength and the crack behaviours of the slag-based ECCs were evaluated and compared with a control mix. The experimental results show that the slag-based ECCs can achieve tensile strain capacity 2.6 %–2.75 % and ultimate tensile strength 1.43 MPa–2.82 MPa at 28 days. It was also found that the ECCs with GGBS and fibres formed few hairline cracks at the gage of the dog bone compared to brittle fracture in the control specimens.

272 Combined rotational atherectomy and intravascular lithotripsy for heavy calcified coronary artery

Aims Percutaneous coronary intervention (PCI) of heavily calcified coronary lesions still represents a challenge for interventional cardiologists, with higher risk of immediate complications, late failure due to stent underexpansion or malapposition and consequent poor clinical outcome. Rotational atherectomy (RA) is a well-known calcium debulking modality. However, when coronary plaques present a significant amount of circumferential deep calcium, RA alone may not be able to achieve adequate lesion preparation. The combined use of intravascular lithotripsy (IVL) and RA, a technique called ‘Rotatripsy’, can be an effective approach in order to enable optimal stent implantation. We present a case of a calcific right coronary artery (RCA) PCI successfully treated by ‘Rotatripsy’ technique. Methods and results A 78-years-old man presented to our emergency department complaining of acute chest pain and dyspnoea. The electrocardiogram revealed ST-segment elevation in aVR and a diffuse ST-segment depression. Transthoracic echocardiography showed left ventricular anterior, septal, and apical walls akinesia. An urgent coronary angiography showed a critical distal left main (LM) stenosis involving the left anterior descending (LAD) artery ostium and a heavy calcified dominant RCA with two tandem sub-occlusive stenosis in the mid segment (Figure 1A). An immediate PCI with two drug eluting stents (DES) in the LM and LAD was performed. The patient was scheduled two days later for RCA PCI. RCA was engaged via left radial approach with a 6-Fr AL1 guiding catheter and the lesions were crossed with a Sion Blue wire. Using a Finecross MG microcatheter, an extra-support Rotawire was placed distally in the RCA. However, after multiple rotablation with 1.5 mm burr (Figure 1B), the mid segment lesion (Figure 1C) was still undilatable with a 3.5 mm non-compliant balloon (NCB) at 22 atm showing a partial dog bone effect (Figure 1D). We decided to attempt adjunctive IVL for calcium debulking. Using a Finecross MG and the trapping technique, a Gran Slam wire was placed distally; a 4.0 mm IVL balloon was delivered at the undilatable lesion and 80 pulses were applied (Figure 1E). Once the IVL treatment was completed (Figure 1F), a 4.0 mm NCB was inflated to 20 atm to further dilate the segment with an optimal expansion (Figure 1G). Finally, a DES Synergy 4.0 × 48 mm was implanted (Figure 1H) and it was post-dilated with a 4.5 mm NCB inflated to 22 atm (Figure 1I) with a perfect angiographic result (Figure 1J). Conclusions Coronary calcifications can lead to stent underexpansion, which is related to a higher rate of future complications, such as restenosis or thrombosis. If conventional lesion dilatations are not effective, alternative techniques should be considered (cutting balloon, scoring balloon, RA, orbital atherectomy, IVL). In case of circumferential deep calcium plaques, RA may not be able to achieve an adequate lesion preparation. RA allows the treatment of intimal calcium and permits to cross balloons or stents through severe lesions. However, when adequate expansion of the balloons is not achieved after RA, Shockwave IVL, that is not usually able to cross critical stenosis due to its bulky profile, represents an optimal complementary device, in order to fracture deep calcium and facilitate stent delivery and optimal expansion. In this case, we have successfully used the hybrid approach called ‘Rotatripsy’, which combines RA and IVL, in order to avoid more aggressive RA, which would have required the use of 7-Fr guiding catheter setting and may have increased the risk of complications.

Effective Young’s Modulus Estimation of Natural Fibers through Micromechanical Models: The Case of Henequen Fibers Reinforced-PP Composites

In this study, Young’s modulus of henequen fibers was estimated through micromechanical modeling of polypropylene (PP)-based composites, and further corroborated through a single filament tensile test after applying a correction method. PP and henequen strands, chopped to 1 mm length, were mixed in the presence of maleic anhydride grafted polypropylene (MAPP). A 4 wt.% of MAPP showed an effective enhancement of the interfacial adhesion. The composites were mold-injected into dog-bone specimens and tensile tested. The Young’s modulus of the composites increased steadily and linearly up to 50 wt.% of fiber content from 1.5 to 6.4 GPa, corresponding to a 327% increase. Certainly, henequen fibers showed a comparable stiffening capacity of PP composites than glass fibers. The intrinsic Young’s modulus of the fibers was predicted through well established models such as Hirsch or Tsai-Pagano, yielding average values of 30.5 and 34.6 GPa, respectively. The single filament test performed to henequen strands resulted in values between 16 and 27 GPa depending on the gauge length, although, after applying a correction method, a Young’s modulus of 33.3 GPa was obtained. Overall, the present work presents the great potential for henequen fibers as PP reinforcement. Moreover, relationships between micromechanics models and filament testing to estimate Young’s modulus of the fibers were explored.

Tension-Compression Fatigue Induced Stress Concentrations in Woven Composite Laminate

Tension-compression (T-C) fatigue response is one of the important design criteria for carbon-fibre-reinforced polymer (CFRP) material, as well as stress concentration. Hence, the objective of the current study is to investigate and quantify the stress concentration in CFRP dog-bone specimens due to T-C quasi-static and fatigue loadings (with anti-buckling fixtures). Dog-bone specimens with a [(0/90),(45/−45)4]s layup were fabricated using woven CFRP prepregs and their low-cycle fatigue behaviour was studied at two stress ratios (−0.1 & −0.5) and two frequencies (3 Hz & 5 Hz). During testing, strain gauges were mounted at the centre and edge regions of the dog-bone specimens to obtain accurate, real-time strain measurements. The corresponding stresses were calculated using Young’s moduli. The stress concentration at the specimen edges, due to quasi-static tension, was significant compared to quasi-static compression loads. Furthermore, the stress concentration increased with the quasi-static loading within the elastic limit. Similarly, the stress concentration at the specimen edges, due to tensile fatigue loads, was more significant and consistent than due to compressive fatigue loads. Finally, the effects of the stress ratio and loading frequency on the stress concentration were noted to be negligible.

LASER SHOCK PEENING INDUCED BACK STRESS MITIGATION IN ROLLED STAINLESS STEEL

Laser shock peening (LSP) is investigated as a potential tool for reducing tensile back stress, shown here applied to rolled and annealed 304L austenitic steel. The back stress of treated and untreated dog-bone samples is extracted from hysteresis tensile testing. Electron back scatter diffraction (EBSD) and orientation imaging microscopy (OIM) analysis quantify the geometrically necessary dislocation (GND) density distribution of unstrained and strained as well as un-peened and peened conditions. Finite element analysis (FEA) simulation models back stress and residual stress development through tensile testing and LSP treatment using known LSP pressure models and Ziegler's non-linear kinematic hardening law. Non-linear regression fitting of tensile testing stress-strain in as-received specimens extracts the kinematic hardening parameters that are used in numerical study. This research shows LSP may be used to overcome manufacturing design challenges presented by yield asymmetry due to back stress in rolled steel.