Test Specimens Research Articles

Synthesis and Characterization of Rebondable Polyurethane Adhesives Relying on Thermo-Activated Transcarbamoylation.

Dynamic polymer networks combine the noteworthy (thermo)mechanical features of thermosets with the processability of thermoplastics. They rely on externally triggered bond exchange reactions, which induce topological rearrangements and, at a sufficiently high rate, a macroscopic reflow of the polymer network. Due to this controlled change in viscosity, dynamic polymers are repairable, malleable, and reprocessable. Herein, several dynamic polyurethane networks were synthetized as model compounds, which were able to undergo thermo-activated transcarbamoylation for the use in rebondable adhesives. Ethylenediamine-N,N,N',N'-tetra-2-propanol (EDTP) was applied as a transcarbamoylation catalyst, which participates in the curing reaction across its four -OH groups and thus, is covalently attached within the polyurethane network. Both bond exchange rate and (thermo)mechanical properties of the dynamic networks were readily adjusted by the crosslink density and availability of -OH groups. In a last step, the most promising model compound was optimized to prepare an adhesive formulation more suitable for a real case application. Single-lap shear tests were carried out to evaluate the bond strength of this final formulation in adhesively bonded carbon fiber reinforced polymers (CFRP). Exploiting the dynamic nature of the adhesive layer, the debonded CFRP test specimens were rebonded at elevated temperature. The results clearly show that thermally triggered rebonding was feasible by recovering up to 79% of the original bond strength.

A comprehensive study on the effects of printing parameters on the mechanical properties of PLA

Purpose This study aims to investigate the effects of five different printing parameters, namely, printing speed (PS), printing temperature/nozzle temperature/extrusion temperature, heated-bed temperature, raster angle (RA) and layer height (LT), on mechanical properties. Design/methodology/approach American Society for Testing and Materials (ASTM) standards were used for the specimen design. Then, the Taguchi method was used for the design of the experiment and an L16 orthogonal array was preferred. Tensile, Shore D and surface roughness tests were conducted on polylactic acid test specimens. The test results were analyzed using the signal-to-noise ratio and analysis of variance (ANOVA). Findings As a result of the study, it was seen that RA is the most important parameter for the tensile strength, PS is for the hardness and LT is for the surface roughness. According to the ANOVA results, the effects of the RA, PS and LT on the maximum tensile strength, hardness and surface roughness were 41.59%, 69.51% and 44.6%, respectively. Originality/value To the best of the authors’ knowledge, this study is one of the most comprehensive parameter optimization studies for additive manufacturing in the literature because it includes five different printing parameters and three mechanical test procedures.

A-059 Validation of self-collected capillary dried blood spot collection for clinical HbA1c testing

Abstract Background The increased prevalence of diabetes in socially disadvantaged populations requires solutions that are amenable to these communities. Unmanaged diabetes can cause cardiovascular disease, kidney damage, blindness, and limb amputation. Diabetes is traditionally diagnosed using fasting/oral glucose tolerance or hemoglobin A1c (HbA1c) tests; both of which require access to medical and laboratory facilities. Self-collected capillary dried blood spot (DBS) testing for HbA1c could alleviate health disparities by offering access to low cost and minimally invasive remote collection. The objective of this study was to validate self-collected capillary DBS specimens for clinical HbA1c testing. Methods DBS HbA1c was measured using the hemolysate application of the Roche cobas c513 Tina-quant Hemoglobin A1cDx Gen.3 assay. Calibration was performed according to the manufacturer’s package insert. Patient samples were prepared by collecting two 3mm DBS punches. Non-biological standards were prepared by placing two blank 3mm DBS punches into an empty tube and adding 10uL of standard. After 24 hours, samples were resuspended in 750uL of hemolyzing reagent and incubated for 75 minutes at room temperature (RT) while shaking at 800 RPM. Preliminary data showed that non-biological standards spotted onto DBS cards did not behave like real patient samples. A correction factor (CF) was derived (n=134) and challenged (n=20) to account for the systematic bias observed between matched patient DBS and venous specimens. Imprecision was established by running two patient DBS specimens as controls. Accuracy was evaluated using residual College of American Pathologists (CAP) proficiency testing (PT) material (n=32). Linearity was confirmed by running 5 levels of Maine Standards Linearity HbA1c Kit in triplicate. Stability of the DBS specimen and the hemolysate supernatant extracted from the DBS specimen were observed at RT. Results Specimens tested between venous and DBS HbA1c to derive the CF (n=134) had a bias of 0.26% (4.32%) and a linear equation of (y=0.938x +0.631; R=0.996). The resulting CF is: reported HbA1c% = (DBS HbA1c% - 0.631)/0.938. Matched venous and DBS specimens that challenged the CF (n=20) had a bias of -0.10% (-1.83%) and a linear equation of (y=1.06x -0.41; R=0.988). Imprecision was 2.3% and 1.3% for patient DBS control specimens with mean concentrations of 5.3% and 5.9%, respectively. Residual CAP PT samples (n=32) had an average bias of -0.05% (-0.40%). DBS HbA1c concentrations from 4.2-15.5% were linear (y=0.903x +1.15; R=0.999). The DBS specimen is stable for 60 days at RT and the hemolysate supernatant is stable for at least 10 hours at RT. Conclusions Self-collected capillary DBS specimens are acceptable for the clinical measurement of HbA1c, and effectively increase accessibility to diabetes screening and monitoring. Applying a CF to DBS patient samples removes the systematic bias observed between matched venous and DBS samples. Non-biological standards and capillary whole blood do not behave the same on DBS cards. Alternative PT for DBS specimens should be investigated as at-home collection advances.

B-276 Evaluation of the Roche Benzodiazepines II Immunoassay for Urine Drug Testing in Clinical Specimens

Abstract Background Benzodiazepines are one of the most commonly prescribed medications in the United States and are frequently linked to instances of abuse and overdose. Historically, FDA-cleared benzodiazepine urine immunoassays cross-react poorly with glucuronidated metabolites excreted in urine. False negative results are especially prevalent with lorazepam, which is almost exclusively excreted as lorazepam glucuronide. Some clinical laboratories have addressed this problem with the addition of beta-glucuronidase to enhance assay sensitivity as a laboratory developed test (LDT). Roche Diagnostics recently received FDA clearance to offer a benzodiazepine immunoassay that includes beta-glucuronidase. Methods Performance characteristics of two FDA-cleared benzodiazepine urine immunoassays (Benzodiazepines Plus, no glucuronidase and Benzodiazepines II, with glucuronidase; Roche Diagnostics) and a benzodiazepine immunoassay LDT (with glucuronidase) were evaluated using 258 urine specimens. These immunoassays were directly compared to an LC-MS/MS benzodiazepine LDT to determine clinical sensitivity and specificity. Cross-reactivity of all three immunoassays were compared and evaluated based on the measured benzodiazepine concentrations determined by the LC-MS/MS LDT. Cross-reactivity for 7-aminoclonazepam, lorazepam, and lorazepam glucuronide were assessed using drug-free urine spiked with reference materials (Cerilliant) at concentrations ranging from 100 to 1000 ng/mL. The cutoff for positive results was set at 1000 mAbs, corresponding to 200 ng/mL of the nordiazepam calibrator. Results The Benzodiazepines II and LDT immunoassays exhibited greater clinical sensitivity (100% and 95.2%) compared to the Benzodiazepines Plus assay (66.7%). Clinical specificity of 100% was observed for all three assays. Cross-reactivity of the Benzodiazepines II assay was greater across the range of benzodiazepine concentrations tested in comparison to the other immunoassays. In particular, the Benzodiazepines II assay was the most sensitive for 7-aminoclonazepam, as it was the only immunoassay out of the three that detected the presence of specimens containing this metabolite alone. Cross-reactivity analysis shows that both 7-aminoclonazepam and lorazepam yielded positive results when tested using the Benzodiazepines II assay at a concentration of 300 ng/ml. 7-aminoclonazepam tested positive at 800 ng/ml with the LDT and Benzodiazepines Plus assays, whereas lorazepam tested positive at 600 ng/ml with these assays. Additionally, the LDT and Benzodiazepines II assays detected lorazepam glucuronide at concentrations of 400 ng/ml and 250 ng/ml, respectively. However, the Benzodiazepines Plus assay yielded negative results for all concentrations of lorazepam glucuronide tested (up to 1000 ng/mL). Conclusions A comprehensive evaluation of these three immunoassays demonstrates that the Benzodiazepines II immunoassay has increased clinical and analytical sensitivity compared to the Benzodiazepines Plus and LDT immunoassays. The inclusion of a beta-glucuronidase greatly improved the sensitivity of the Benzodiazepines II and LDT immunoassays for lorazepam, which is primarily excreted as a glucuronide metabolite in urine.

B-259 Cannabinoid Prevalence in Umbilical Cord Tissue Toxicity Testing

Abstract Background Cannabis is rapidly becoming legalized in the United States. While its effects on the developing fetus are not fully understood, current recommendations advise against cannabis use and exposure during pregnancy due to its association with negative outcomes, such as preterm birth, fetal growth restriction, low birth weight, and developmental deficits. If drug exposure is suspected, umbilical cord tissue (UCT) testing is growing in frequency as a tissue of choice when testing infants. Neonatal testing protocols vary between hospitals, including both targeted or universal collection and targeted or universal testing of neonatal specimens. Based on the current environment of legalization, we were curious to see what the changes in cannabis use were over the previous five years, from 2019-2023. Methods We queried our laboratory information system for reported findings from screening and confirmatory umbilical cord testing, both of which were analyzed via liquid chromatography tandem-mass spectrometry (LC-MS/MS). Results were analyzed using R coding software. Results Overall, annually, 2019-2023 positivity rates for testing in general ranged from 41% - 44% positivity and maintained at 44% from 2020 onwards (n=90384 total workorders 2019-2023, n=40551 total positive workorders). Cannabinoids were starkly the most common drug found, accounting for 59-63% of all positive workorders annually from 2019-2023. There were no statistically significant differences in the cannabinoid positivity rates between 2019-2023. Of note, cannabinoid-only (delta-9-carboxy THC) workorders accounted for 28% of all positive workorders (n=25962) during that time frame. This was followed by methamphetamine-only (n=2485 workorders) and buprenorphine-only (n=1765 workorders). The combination of cannabinoids and methamphetamine, the most common drug combination found in UCT testing, had a range of positive results from 2019 - 2023 of 2.9 - 3.6% (n=1327 workorders). Cannabinoids and cocaine, the second most prevalent drug combination, ranged in positivity from 1.3 - 1.6% from 2019-2023 (n=616 workorders). Conclusions Cannabinoid exposure is prevalent in pregnant individuals undergoing UCT testing. Physicians should take care to keep informed on the impacts of cannabis exposure on the developing fetus and educating clients on the effects of cannabis exposure during pregnancy.

Study the Effect of Adding Malic Anhydride and Carbon Fibers to the Mechanical and Morphology Properties of Polypropylene

Adding reinforcement materials like carbon fibers with maleic anhydride improves the strength of polypropylene. The present work aimed to study the effect of adding maleic anhydride and carbon fibers on the mechanical properties of polypropylene enhanced by presenting carbon fibers. Carbon fibers added at different ratios (0, 2, 4, 6, and 8) % and 1% of maleic anhydride were added to pure polypropylene. Standard tensile and impact test specimens were prepared per ASTM standards using an extruder technique. It was observed that increasing the carbon fiber content enhanced the tensile strength, modulus of elasticity, and hardness of polypropylene while the elongation decreased, but it enhanced after MAH addition. SEM and FTIR indicated good adhesion between fibers and polypropylene after adding maleic anhydride (MAH). UV tests showed that carbon fibers protect the composite material from the UV sunlight.

The improvement of dry sliding tribological properties by designing nano-primary cementite in bainitic/martensitic matrix microstructure in hypereutectoid PM components

The production of nano-sized primary cementite in bainite/martensite matrix (NCBM) microstructure was designed to improve the dry sliding wear properties of high carbon PM parts. A different heat treatment cycle was carried out for the production of novel the NCBM microstructure. High purity iron powder 1.5 wt%. natural graphite powder was added and it was compacted in the form of a dry sliding wear test specimen in a mold and sintered at 1200 °C in a pure Ar gas atmosphere. The novel NCBM microstructure in the PM material was produced by quenching at 950 °C, then annealing at 600 °C for 12 min, then quickly cooling from 730 °C to 250 °C in a salt bath and keeping it isothermal for 100 s. The friction coefficient of materials with NCBM microstructure was less than other samples. It was found that while the wear coefficient were higher in the tempered martensitic microstructure sample having higher hardness, they were less than in the sample having bainitic/martensitic microstructure with similar hardness.

Effects of Genipin Crosslinking of Porcine Perilimbal Sclera on Mechanical Properties and Intraocular Pressure.

The mechanical properties of sclera play an important role in ocular functions, protection, and disease. Modulating the sclera's properties by exogenous crosslinking offers a way to expand the tissue's range of properties for study of the possible influences on the eye's behavior and diseases such as glaucoma and myopia. The focus of this work was to evaluate the effects of genipin crosslinking targeting the porcine perilimbal sclera (PLS) since the stiffness of this tissue was previously found in a number of studies to influence the eye's intraocular pressure (IOP). The work includes experiments on tensile test specimens and whole globes. The specimen tests showed decreased strain-rate dependence and increased relaxation stress due to the cross-linker. Whole globe perfusion experiments demonstrated that eyes treated with genipin in the perilimbal region had increased IOPs compared to the control globes. Migration of the cross-linker from the target tissue to other tissues is a confounding factor in whole globe, biomechanical measurements, with crosslinking. A novel quantitative genipin assay of the trabecular meshwork (TM) was developed to exclude globes where the TM was inadvertently crosslinked. The perfusion study, therefore, suggests that elevated stiffness of the PLS can significantly increase IOP apart from effects of the TM in the porcine eye. These results demonstrate the importance of PLS biomechanics in aqueous outflow regulation and support additional investigations into the distal outflow pathways as a key source of outflow resistance.

Enhanced fatigue SN curve generation for gear bending fatigue life prediction using multi-objective optimization algorithms

This study presents a comprehensive methodology for fatigue life prediction and SN curve generation in gear systems, integrating specimen and product-level testing, simulations, and multi-objective optimization. The approach addresses the discrepancy between specimen-based testing and actual product performance through a novel multi-fidelity framework. To solve the proposed multi-objective optimization problem, several optimization algorithms were compared and analyzed, demonstrating the effectiveness of each approach in balancing different objectives. A key innovation is the development of an empirical formulation-based surrogate model, enabling efficient optimization while significantly reducing computational demands. The methodology covers both specimen and product-level testing along with simulations, offering a holistic solution for accurate fatigue life prediction. Extensive validation through experiments and comparison with commercial software confirms the reliability and practical applicability of the method. This approach provides a sustainable and efficient solution for SN curve generation and fatigue life prediction in automotive gear train development, allowing for continuous improvement as new data becomes available. Its practicality and accuracy make it particularly valuable for early-stage design optimization and large-scale applications in the automotive industry.

On Microplasticity-induced Fatigue Fracture and its Relation to Entropy

Abstract The study delves into the intricate effects of microplasticity on fracture formation in testing specimens under axial cyclic loading. The primary aim is to pinpoint the juncture at which microplasticity becomes discernible across the stress cycle. Fatigue tests are conducted on varied specimens until failure using a fatigue testing machine, while recording parameters such as frequency, stress amplitude, applied power, and tensile strain. The investigation seeks to ascertain whether cracks must attain a specific size before manifesting these subtle alterations. A conjectured relationship is proposed between the number of cycles and entropy throughout the process. Additionally, a hypothesis is posited suggesting that microplasticity emerges only once the crack surpasses a certain threshold, such as grain size. This research provides insights into material fracture mechanisms and their implications for product durability and safety. Such discernments into the product life cycle under analogous conditions hold promise for delineating operational limits.

Characterisation of 18Ni 300 steel CT specimens in a fatigue test manufactured by selective laser melting at 0°, 45° and 90°

Maraging steel, 18Ni300, is a high-performance material that shows promising potential for various industrial applications. Employing Selective Laser Melting, it is utilized in the production of high-value components. Understanding the fatigue mechanisms of this material is imperative, as its fatigue life is influenced by both surface and internal porosity, as well as defects produced when manufacturing the objects due to the patterns used. The main objective is to analyze the characterization of these pores and clarify their relationship with the fatigue properties of the material under study. Compact tension specimens were manufactured by selective laser melting at three angles (0°, 45° and 90°) with respect to the crack growing direction and fatigue tests were performed. A study of the porosity of the sample was conducted, which established a correlation between the printing angle, growing rate (da/dN curves), and the porosity that is categorised through the aspect ratio and the circularity ratio. It is shown that all manufacturing orientations generate similar pore sizes and area, but the 45° orientation induces pore with slightly higher circularity ratio. The results indicate that the faster fatigue crack growth might be linked to the slight increase in circularity, and this was observed for 45°.

Low-Frequency Magnetic Incremental Permeability for the Non-destructive Evaluation of Hardness Profile After Carburization Treatment with Large Case Hardening Depth

Carburization treatment with large case hardening depth is a technical process to enhance steel parts' surface hardness and wear resistance. Accurate evaluation of this metallurgical treatment is crucial to prevent critical mechanical failures. Low-frequency magnetic incremental permeability (LF-MIP) emerges as a non-destructive surface technique well-suited for this purpose in the case of ferromagnetic parts. Although correlations between magnetic indicators obtained through LF-MIP characterization and deep carburization treatment have been demonstrated, they remain qualitative. In this study, we propose an innovative method to assess the entire hardness profile based on LF-MIP characterization. Experimental results and simulation data are integrated into a reference chart used for post-processing, enabling the prediction of hardness profiles for specimens in a blind test. With a relative Euclidean distance of less than 6% between the method's predictions and destructive tests conducted on specimens treated with medium, deep, and intense intensities, we consider the method validated.

Acoustic Emission Energy Release Rate Model for Classification of Damage Development in Large Fiber Reinforced Plastic Composite Structures

Acoustic emission identification of fracture mechanisms in composite materials is of great importance for the practical assessment of the serviceability of aerospace structures, such as unmanned aerial vehicles, rocket motors, and others. Many scientific research studies conducted in recent decades have demonstrated the unique capabilities of the Acoustic Emission (AE) method to detect and identify different failure mechanisms, including fiber breakage, matrix cracking, and delaminations in fracture tests of composite specimens. However, testing large composite structures, in many cases, can be accompanied by multiple time-overlapped fracture events activated simultaneously, resulting in considerable difficulties in the classification and assessment of combined prolonged AE signals. In this work, we propose the Energy Release Rate (ERR) model for the classification of AE activity related to fiber-reinforced plastic (FRP) composite fracture. The model identifies accurately both micro-scopic and macro-scopic fracture mechanisms in large aerospace structures having complex composition of materials. The model is practically applied using several machine learning methods and provides a simple means to identify and discriminate typical fracture mechanisms and their combinations. Specifically, we describe ERR model, the choice of most informative AE parameters, the choice of suitable machine learning classification methods, their training and testing on FRP specimens, and validating the model in practical tests of large full-size FRP composite structures.

A peridynamic compensated critical energy density criterion for mixed-mode fracturing in quasi-brittle materials

This study integrates a compensated critical energy density criterion (CCED) into the ordinary state-based peridynamics framework to enable detailed analysis of mode I, mode II, and mixed-mode fracturing. The proposed bond failure criterion builds upon the advantages of the traditional critical energy density (CED) to enable precise calculation of strain energy density. Additionally, the critical bond rotation criterion (CR) is employed to account for shear bonds that the CED might overlook. Using the peridynamic differential operator (PDDO) format in formulating the entire computational framework enhances both accuracy and numerical stability. The model’s validation is conducted through benchmark examples, including the mode I double cantilever beam test, the mode II compact shear test, and a mixed-mode mechanical fracturing test in pre-notched specimens with central borehole loading. Convergence studies, comparative analyses with finite element method simulations and theoretical solutions thoroughly examine the proposed model’s performance and accuracy.

Membandingkan Kekuatan Pengelasan Single Dan Double Kawat Inti Elektroda (Filler Rod) Menggunakan Las Smaw

Advances in welding technology are very helpful in making, repairing or repairing chassis jobs that have a high level of difficulty and requirements. Especially in the chassis, many welding elements are involved because welded joints have an important role to support the body, engine, and vehicle load. In practical work at CV. Pringgandani Welding Analysis Comparing the Strength of Welding Results of Single Electrode Core Wire and Double Electrode Core Wire (Filler Rod) Using SMAW welding which is carried out for chassis welding which is claimed by mechanics in welding with a depth and width of more than 5 mm, it is better to use double electrode core wire which can speed up and strengthen the weld. Then a test is carried out to prove the results of the Single Wire Electrode Core and Double Electrode Core Wire (Filler Rod) welds which are stronger and faster in the process. By testing the weld results on an iron plate with dimensions of 250 mm x 50 mm x 10 mm, the welding process uses the SMAW (Shielded Metal Arc Welding) welding method. Using an E6013 type electrode with a diameter of 2 mm with a current of 90 A, polarity DCEP (Direct Current Electrode Positive) The welding position used is the 1G position or horizontal position with the welding process using a single v-groove bevel butt joint and an angle of 60o with a weld width of 10 mm and a weld depth of 8 mm. The plate samples used were two samples. In sample 1 using a single wire core electrode, and sample 2 using a double wire core electrode. All samples were made of tensile test specimens with the ASME-IX standard, a tensile test was carried out to determine and prove the respective strengths of the welding results of Single Wire Core Electrode and Double Wire Core Electrode (Filler Rod).

Environmentally Friendly Paving Block Based on Wood Waste: The Effect of Rubber Wood Waste Content on the Physical-Mechanical Properties of Paving Block

The wood sawing industry generates significant waste, consisting of wood chips, wood scraps, and sawdust. This research aims to evaluate the effect of rubber wood sawdust addition on the moisture content, water absorption capacity, and compressive strength of paving blocks. The study was conducted in August–September 2023, starting with preparing raw materials, composition planning, and test specimen fabrication. The parameters in this study included density testing, moisture content, water absorption capacity, and compressive strength. The density test results for treatments P0 were 1.11 g/cm3, P1 1.09 g/cm3, P2 1.07 g/cm3, P3 1.08 g/cm3, and P4 1.09 g/cm3. The moisture content test yielded values of 11.38% for P0, 12.56% for P1, 12.94% for P2, 13.24% for P3, and 13.80% for P4. The water absorption capacity values obtained were, for P0, 5.17%; P1, 5.40%; P2, 6.36%; P3, 8.11%; and P4, 9.27%. Compressive strength tests produced values for P0 at 7.19 N/mm2, P1 at 5.67 N/mm2, P2 at 4.22 N/mm2, P3 at 3.48 N/mm2, and P4 at 3.07 N/mm2. The addition of rubber wood sawdust to paving blocks significantly influences density, moisture content, water absorption capacity, and compressive strength values. Keywords: Composition, Compressive strength, Paving block, Sawdust waste.

Evaluation and quantification of diffusion wear between cutting chip and workpiece using forging press

The state of the interface between the workpiece and the cutting tool affects the cutting temperature and pressure on the tool surface during the cutting process. In particular, while cutting difficult-to-cut materials such as Ni-based alloy 718, the workpiece exhibits a high affinity for cutting tool materials and could easily adhere to them. Adhesion can, at times, adversely affect productivity. The diffusion between the cutting tool and the workpiece is a factor considered to contribute to the adhesion phenomenon during cutting. Addressing this issue involves choosing tool materials and coated materials with high resistance to diffusion and optimizing cutting conditions, particularly the cutting speed, which significantly impacts cutting temperature. However, because cutting tool wear comprises various forms, clarifying the effect of diffusion on tool wear remains open. In this study, to reproduce the diffusion phenomenon between cutting tool and workpiece, two pairs of test specimens were prepared: (1) cemented carbide-AISI 1045 and (2) cemented carbide-Alloy718, which could be held at high temperature under vacuum conditions by a forging press. The degree of diffusion phenomena was evaluated at each tool-work material interface, and the quantification of diffusion amount was performed by diffused element in each work material. Additionally, the theoretical analysis of the diffusion phenomenon using the thermodynamic and phase diagram calculation software Thermo-Calc was also performed.

Constitutive modelling of deformation rate dependent response of steel timber shear connections

This paper presents experimental and numerical investigations into the deformation rate-dependent constitutive response of steel-timber shear connections with screws. After describing the test specimens and experimental arrangement, a detailed account of the complete deformation response and main mechanical parameters of the tested shear connections under three applied displacement rate levels are given. Specimens with small screw diameters had a relatively brittle response, failing shortly after yielding, whilst those with higher diameters showed ductile failure modes, with plastic hinges forming in the screws and concurrent extensive timber crushing. It was observed that the stiffness increases with the deformation rate due to the viscoelastic response of wood materials, whilst the peak load is largely constant. Nonlinear finite element simulations were carried out to validate the main numerical parameters for steel, timber, and interaction characteristics. After gaining confidence in the ability of the numerical models to predict closely the stiffness and peak load, numerical investigations were carried out to examine the influence of key material and geometric parameters on the stiffness, load resistance and deformation response. The studies showed that higher timber strength increases the initial stiffness and the peak load, while higher screw grades improved both stiffness and strength. Based on the results and observations, code-modified expressions for evaluating the stiffness and load resistance, as a function of the deformation rate, are proposed within the ranges considered, and validated against a collated database. Comparative assessments with existing literature indicate that the proposed equations provide improved estimates. Suggested closed-form relationships enable the characterisation of the full constitutive response of steel-timber shear connections, that can be adopted for discrete nonlinear modelling of connectors.

Determination of process parameters for additive manufacturing with Inconel 718 powder

Abstract In this study, the additive manufacturing (AM) of Inconel 718 was investigated, and the processing parameters can affect the mechanical properties of the product. The five-axis laser cladding composite processing machine Tongtai AMH-630 is used, and the laser power is set to 800W based on the thermal impact of the laser on the base plate. However, the laser scanning speed (600-1200mm/min) and powder feed rate (3~15g/min) are not arbitrary combinations. It is recommended to present the feed per unit length in g/mm, which seems to be more clearly expressed. Regardless of changes in laser scanning speed and wheel speed, it is a reasonable decision to control the combination of the two at about 0.01-0.013g/mm. Through single-pass cladding experiments, we select different combinations of laser scanning speed and powder feed rate with a cladding aspect ratio in the range of 3:1 to 4:1. In the multi-pass cladding experiment, an overlap rate of 30% was used as the plane cladding spacing; a spacing of 80% of the cladding height was used as the stacking height. This study uses scanning speeds of 600, 700, 800, 1000 and 1200mm/min to clad a rectangular body. Tensile test specimens were processed using a CNC lathe, and tensile tests were conducted to obtain variations in tensile strength and elongation at different scanning speeds. The mechanical properties of both will decrease as the scanning speed increases. At a scanning speed of 600mm/min, its tensile strength is comparable to that of Inconel 718 standard materials; but its elongation is 61% of that of standard materials. If Hot Isostatic Pressing (HIP) is applied after cladding, it seems that a higher scanning speed can achieve a performance closer to that of standard materials.

Seismic loading assessment of a novel structural column testing equipment

In experimental investigation on seismic performance of structural columns, it is particularly important that the loading device can reproduce a structure’s gravity load and apply a lateral seismic load at the same time, and both should be decoupled. Based on this concept, a two-dimensional multi-usage structural testing equipment (ZJU-MUST) has been developed with the following features: (1) the horizontal loading is ensured perpendicular to the vertical loading, and the loads in different directions are decoupled; (2) horizontal and vertical forces applied to testing specimen can be directly measured without the need to correct the secondary effects due to friction or vertical loading; (3) it is more reliable and suitable for cyclic loading under variable vertical forces. A 2600 mm high steel tubular column was designed for both cyclic loading tests and pseudo-dynamic tests. From the column test, the control system of ZJU-MUST as well as its performance in real-time data transmission and calculation can be verified.