Search

The article explores the challenges faced by automotive manufacturers in reducing fatigue tests on prototypes through numerical simulations. It introduces the probabilistic Dang Van criterion to identify critical zones in mechanical components more effectively. By utilizing historical design data and positive-unlabeled learning, the study proposes a novel approach to enhance the predictive accuracy of fatigue criteria. The text discusses the estimation of fatigue criteria for mechanical parts using a probabilistic approach, emphasizing the importance of testing conditions and parameter estimation for accurate predictions. Results indicate that PU learning models outperform traditional methods in predicting critical zones on complex automotive parts, suggesting potential improvements in design processes. [Extracted from the article] more...

Hydrogels are flexible materials that typically accommodate elongation with positive Poisson's ratios. Auxetic property, i.e., the negative Poisson's ratio, of elastic materials can be macroscopically implemented by the structural design of the continuum. We realize it without mold for hydrogel made of cellulose nanofibers (CNFs). The complex structural design of auxetic Kirigami is first implemented on the dry CNF film, i.e., so-called nanopaper, by laser processing, and the CNF hydrogel is formed by dipping the film in liquid water. The CNF films show anisotropic swelling where drastic volumetric change mainly originates from increase in the thickness. This anisotropy makes the design and fabrication of the emergent Kirigami hydrogel straightforward. We characterize the flexibility of this mechanical metamaterial made of hydrogel by cyclic tensile loading starting from the initial end-to-end distance of dry sample. The tensile load at the maximum strain decreases with the increasing number of cycles. Furthermore, the necessary work up to the maximum strain even decreases to the negative value, while the work of restoration to the original end-to-end distance increases from the negative value to the positive. The equilibrium strain where the force changes the sign increases to reach a plateau. This plastic deformation due to the cyclic loading can be regarded as the adaptive response without fracture to the applied dynamic loading input. IMPACT STATEMENT: Highly anisotropic swelling-based gelation of dry film of cellulose nanofibers enables development of emergent hydrogel Kirigami with auxetic behavior. Furthermore, adaptive response to the iterative loading condition is found. [ABSTRACT FROM AUTHOR] more...

The shear stress on isotropic curved beams with compact sections and variable thickness is investigated. Two new solutions, based on Cook's proposal and the mechanics of materials approach, were developed and validated using computational finite element models (FEM) for four typical cross-sections (rectangular, circular, elliptical, and triangular) used in civil and mechanical structures, constituting a novel approach to predicting shear stresses in curved beams. They predict better results than other reported equations, are simpler and easier for engineers to use quickly, and join the group of equations found using the theory of elasticity, thereby expanding the field of knowledge. The results reveal that both equations are suitable to predict the shear stress on a curved beam with outer/inner radii ratios in the interval 1 < b / a ≤ 5 aspect ratios. There is a maximum relative difference between the present solutions and finite element models of 8% within 1 < b / a ≤ 2, and a maximum of 16% in 2 < b / a ≤ 5. Additionally, the neutral axis of the curved beam can be located with the proposed solution and its position matches with that predicted by FEM. The displacement at the top face of the end of the curved beam induces a difference in the shear stress results of 8.0%, 7.0%, 6.5%, and 2.9%, for the circular, rectangular, elliptical, and triangular cross-sections, respectively, when a 3D FEM solution is considered. For small b / a ratios (near 1), the present solutions can be reduced to Collignon's formula. [ABSTRACT FROM AUTHOR] more...

The mechanical methods for measuring residual stresses typically rely on so-called destructive techniques where some stress components can be determined based on part deflection after material removal (cutting, etching, drilling, etc.). While these methods don't provide a comprehensive representation of residual stresses within the entire part, they can be readily applied in most manufacturing labs. In this study, we propose an efficient method for determining residual stress within additively manufactured cylindrical samples of stainless steel. The method is based on the assumption of a relation between the axial component of residual stress (normal to cross-section) and the cylinder radius. The general form of this relation is proposed based on data from numerical simulations using linear, parabolic or piecewise approximations. The parameters for the proposed relation are defined using equilibrium equations for total force and moment. The proposed method relies on an experiment with a mechanical cut along the cylinder. Consequently, the deflection of the cylinder halves after the cut allows for obtaining the equivalent bending moment more...

This article discusses a method for estimating residual stresses in metal samples produced by additive manufacturing, specifically focusing on steel cylindrical bars produced by laser powder bed fusion (LPBF). The method involves making a partial longitudinal cut in the bar using electrical discharge machining (EDM) and measuring the resulting deflection to assess the contribution of residual stresses. The study combines experimental analysis with numerical simulation using finite element modeling (FEM). The proposed method allows for the estimation of residual stresses in the laboratory without the need for special equipment. The article also provides a list of references that cover various topics related to residual stresses and mechanical properties of additively manufactured stainless steel, which can be useful for further research. [Extracted from the article] more...

Background: Shear forces related to friction are one of the risk factors shown to increase the likelihood of wheelchair users developing pressure injuries (PIs), especially in the buttocks region. Thus, reducing the coefficient of friction between the seat and the person's pants could be a means toward reducing the incidence of PIs. Objective: This study aimed to: (1) determine the coefficients of friction of seven commonly worn pant fabrics and two seat cover fabrics and (2) investigate the effects of a deformable seat cushion on the measurement of the coefficients of friction. Methods: A mechanical system (termed sled) had a pants fabric secured to its bottom and was placed on top of a custom seat pan with seat cover. The seat pan was tilted from horizontal until the sled system started to slide on the seat pan. The coefficient of friction between the two fabrics was calculated using kinematics data obtained from a motion capture system. Results: The office fabric seat cover produced smaller coefficient of friction than the vinyl seat cover for all of the pant fabrics. Women's khakis demonstrated one of the smallest coefficients of friction, and denim demonstrated one of the largest coefficients of friction consistently across both seats covers. Conclusion: Replacing traditional vinyl seat covers in wheelchairs with a fabric closer to an office seat fabric is one approach to reducing frictional forces at the seat interface. Although optimal pant fabrics can be identified for shear force reduction, the results also depend on the seat cover fabric. [ABSTRACT FROM AUTHOR] more...

This paper is concerned with the determination of the yield surface in a two-dimensional stress field within an undergraduate Mechanics of Materials student laboratory experiment. In this experiment, the two-dimensional stress field is obtained by subjecting a steel specimen to a combined bending and torsion load. The motivation for the paper was the lack of correlation between the von Mises and Tresca yield criteria and the principal stresses calculated at the load at which students were predicting material yielding. The latter yield loci were based on the uniaxial 0.2% proof stress. The lack of correlation was creating a lot of frustration amongst students. This is undesirable, especially within an undergraduate student experiment. Two hypotheses for the lack of agreement were considered. The first hypothesis was the uncertainty involved in the method that the students were using to predict the onset of material yielding. The second hypothesis was that the specimens being used for the experiment had anisotropic properties, given that little information on their manufacture was provided. The need for determining accurate yield stress values and on methodologies found in literature that are used to determine the material proof stress or lower yield stress in a uniaxial tensile test are discussed. Four methods taken from literature are used and adapted to detect the first yield of the specimen under a combined bending and torsional load. The resulting experimentally yield loci are compared with the theoretical von Mises and Tresca isotropic yield loci over half of the second quadrant of the two-dimensional principal stress field plot. Correlation between the four methods was quite good but not so when compared with the von Mises and Tresca' loci. A lack of correlation occurred for an increasing torsional load indicating a possible anisotropy in the material properties. These results hinted towards the second hypothesis. A number of tensile test specimens were hence heat treated so as to induce isotropy in the material properties. The combined loading experiments were repeated using the heat-treated samples. A very good correlation was obtained between the experimental yield points for the two-dimensional stress field and the von Mises and Tresca yield loci. This good correlation for the heat-treated specimens confirmed the authors' second hypothesis on the anisotropic properties in the as-received state and, therefore, the requirement to heat treat the specimens for a meaningful student undergraduate laboratory activity. [ABSTRACT FROM AUTHOR] more...

A methodology is presented to find either implicit or explicit relations, called syzygies, between invariants in a minimal integrity basis for n symmetric second-order tensors defined on a three-dimensional euclidean space. The methodology i) yields explicit non-polynomial expressions for certain invariants in terms of the remaining invariants in the integrity basis and ii) allows the construction of the implicit relations. The results of this investigation are important in modeling biological structures, which, in general, are non-homogeneous and made of anisotropic viscoelastic materials that are subjected to large deformations and are modeled through constitutive relations that depend on symmetric tensors. [ABSTRACT FROM AUTHOR] more...

Objective: The present study aimed to investigate the effects of blood flow restriction training on muscle strength, bone tissue structure material, and biomechanical properties in rats applying various exercise interventions and to analyze the process by identifying the bone turnover markers, it provides a theoretical basis for the application of BFRT in clinical rehabilitation. Methods: A total of 24, 3-month-old male SD (Sprague Dawley) rats were randomly divided into pressurized control group (CON, n=6), low-intensity training group (LIRT, n=6), high-intensity training group (HIRT, n=6), and blood flow restriction training group (LIBFR, n=6) for 8-week ladder-climbing exercises. The pressured control group were given only ischemia treatments and did not undertake any burden. The low-intensity training group was allowed to climb the ladder with 30% of the maximum voluntary carrying capacity (MVCC). The rats in the high-intensity training group were allowed to climb the ladderwith 70% MVCC. The blood flow restriction training group climbed the ladder with 30%MVCC while imposing blood flow restriction. Before sampling, the final MVCC was measured using a ladder-climbing protocol with progressively increasing weight loading. The serum, muscle, and bone were removed for sampling. The concentrations of the bone turnover markers PINP, BGP, and CTX in the serum were measured using ELISA. The bone mineral density and microstructure of femur bones were measured using micro-CT. Three-point bending and torsion tests were performed by a universal testing machine to measure the material mechanics and structural mechanics indexes of the femur bone. Results: The results of maximum strength test showed that the MVCC in LIRT, HIRT, and LIBFR groups was significantly greater than in the CON group, while the MVCC in the HIRT group was significantly higher than that in the LIRT group (P<0.05). According to the results of the bone turnover marker test, the concentrations of bone formation indexes PINP (amino-terminal extension peptide of type I procollagen) and BGP (bone gla protein) were significantly lower in the CON group than in the HIRT group (P<0.01), while those were significantly higher in the LIRT group compared to the HIRT group (P<0.01). In terms of bone resorption indexes, significant differences were identified only between the HIRT and other groups (P<0.05). The micro-CT examination revealed that the HIRT group had significantly greater bone density index values than the CON and LIRT groups (P<0.05). The results of three-point bending and torsion test by the universal material testing machine showed that the elastic modulus and maximum load indexes of the HIRT group were significantly smaller than those of the LIBFR group (P<0.05). The fracture load indexes in the HIRT group were significantly smaller than in the LIBFR group (P<0.05). Conclusion: 1. LIRT, HIRT, LIBFR, and CON all have significant differences, and this training helps to improve maximum strength, with HIRT being the most effective. 2. Blood flow restriction training can improve the expression of bone turnover markers, such as PINP and BGP, which promote bone tissue formation. 3. Blood flow restriction training can improve muscle strength and increase the positive development of bone turnover markers, thereby improving bone biomechanical properties such as bone elastic modulus and maximum load. [ABSTRACT FROM AUTHOR] more...

Hardness is one of the most important mechanical properties of materials, since it is used to estimate their quality and to determine their suitability for a particular application. One method of determining quality is the Vickers hardness test, in which the resistance to plastic deformation at the surface of the material is measured after applying force with an indenter. The hardness is measured from the sample image, which is a tedious, time-consuming, and prone to human error procedure. Therefore, in this work, a new automatic method based on image processing techniques is proposed, allowing for obtaining results quickly and more accurately even with high irregularities in the indentation mark. For the development and validation of the method, a set of microscopy images of samples indented with applied forces of 5 N and 10 N on AISI D2 steel with and without quenching, tempering heat treatment and samples coated with titanium niobium nitride (TiNbN) was used. The proposed method was implemented as a plugin of the ImageJ program, allowing for obtaining reproducible Vickers hardness results in an average time of 2.05 seconds with an accuracy of 98.3 % and a maximum error of 4.5 % with respect to the values obtained manually, used as a golden standard. [ABSTRACT FROM AUTHOR] more...

Extrusion 3D-printing of biopolymers and natural fiber-based biocomposites enables the fabrication of complex structures, ranging from implants' scaffolds to eco-friendly structural materials. However, conventional polymer extrusion requires high energy consumption to reduce viscosity, and natural fiber reinforcement often requires harsh chemical treatments to improve adhesion. We address these challenges by introducing a sustainable framework to fabricate natural biocomposites using Chlorella vulgaris microalgae as the matrix. Through bioink optimization and process refinement, we produced lightweight, multifunctional materials with hierarchical architectures. Infrared spectroscopy analysis reveals that hydrogen bonding plays a critical role in the binding and reinforcement of Chlorella cells by hydroxyethyl cellulose (HEC). As water content decreases, the hydrogen bonding network evolves from water-mediated interactions to direct hydrogen bonds between HEC and Chlorella, enhancing the mechanical properties. A controlled dehydration process maintains continuous microalgae morphology, preventing cracking. The resulting biocomposites exhibit a bending stiffness of 1.6 GPa and isotropic heat transfer and thermal conductivity of 0.10 W/mK at room temperature, demonstrating effective thermal insulation. These characteristics make Chlorella biocomposites promising candidates for applications requiring both structural performance and thermal insulation, offering a sustainable alternative to conventional materials in response to growing environmental demands., (© 2024 Wiley‐VCH GmbH.) more...

Cross Laminated Timber (CLT) has been considered a feasible and sustainable option as a building material for many building applications. However, lowering costs and the ability to use a wide spectrum of lower quality lamstock can be critical for this product growth. Off-spec timber often has a significant number of out-plane defects that prevent the lamstock from lying flat and creating an intimate bond between the corresponding CLT layers. This paper aims to introduce a mechanical model to estimate the amount of pressure that makes a warped lumber flat and allow proper contact for an adhesive bond. The difference between experimental and theoretical values were less than 5 kPa for most samples analyzed. The proposed model is an important step to allowing low-quality lumber associated with out-of-plane defects to be further explored by the wood industry in order to create new options for CLT feedstock. This is especially true when considering utilization of small diameter timber (SDT), which is often not considered a viable option for many CLT lamstocks. As a desired outcome, this could minimize losses and optimize industrial manufacturing by using low-quality materials that would positively impact the forest health and mitigate wildfires, while creating economic opportunities. [ABSTRACT FROM AUTHOR] more...

Microalloyed steels offer a good combination of desirable mechanical properties by fine-tuning grain growth and recrystallization dynamics while keeping the carbon content low for good weldability. In this work, the dislocation density evolution during hot rolling was correlated by materials modeling with flow curves. Single-hit compression tests at different temperatures and strain rates were performed with varying isothermal holding times prior to deformation to achieve different precipitation stages. On the basis of these experimental results, the dislocation density evolution was evaluated using a recently developed semi-empirical state-parameter model implemented in the software MatCalc. The yield stress at the beginning of the deformation σ0, the initial strain hardening rate θ0, and the saturation stress σ∞—as derived from the experimental flow curves and corresponding Kocks plots—were used for the calibration of the model. The applicability for industrial processing of many microalloyed steels was assured by calibration of the model parameters as a function of temperature and strain rate. As a result, it turned out that a single set of empirical equations was sufficient to model all investigated microalloyed steels since the plastic stresses at high temperatures did not depend on the precipitation state. [ABSTRACT FROM AUTHOR] more...

Summary: Buckling is a loss of structural stability. It occurs in long slender structures or thin plate structures which is subjected to compressive forces. For the structural materials, such a sudden change in shape has been considered to be avoided. In this study, we utilize the Au nanowire’s buckling instability for the electrical measurement. We confirmed that the high-strength single crystalline Au nanowire with an aspect ratio of 150 and 230-nm-diameter shows classical Euler buckling under constant compressive force without failure. The buckling instability enables stable contact between the Au nanowire and the substrate without any damage. Clearly, the in situ electrical measurement shows a transition of the contact resistance between the nanowire and the substrate from the Sharvin (ballistic limit) mode to the Holm (Ohmic) mode during deformation, enabling reliable electrical measurements. This study suggests Au nanowire probes exhibiting structural instability to ensure stable and precise electrical measurements at the nanoscale. more...

Highlights: Analytically modeling the effect of eccentricity on flexible crankshaft and piston secondary motion; Analytically modeling the eccentricity of the crankshaft; Analytically modeling the absolute value of the dynamic displacement of the center of the crankshaft; Showing how sensitive the dynamic displacement in flexible crankshafts is to the changes in its independent variables; Double experimental validation of the analytical models based on the eccentricity of the crankshaft and based on fatigue analysis; A proposed approach of fatigue failure analysis for vehicular dynamic components; A proposed nanostructure of crankshafts for improved structural mechanics. In spite of the fact that the flexibility of the crankshaft of diesel engines exhibits notable nonlinearities, analytical modeling of such nonlinearities is not yet realized. The present study thus analytically models the effect of eccentricity on flexible crankshaft and piston secondary motion. The eccentricity of the crankshaft is modeled as the summation of the hydrodynamic eccentricity and the dynamic mass eccentricity of the crankshaft. The study also models the absolute value of the vibrational dynamic displacement of the center of the crankshaft. The paper proves that such dynamic displacement of the center of the crankshaft is sensitive to the changes in its independent variables. It was found that the most influential parameters on the dynamic displacement of the center of the crankshaft due to vibration are the natural frequency and the eccentricity of the crankshaft. The modeling of the dynamic displacement in a flexible crankshaft was validated using a case study based on the eccentricity of the crankshaft showing a relative error of 4%, which is less than the relative error in the CMEM and GT-Power. Furthermore, the analytical modeling of the dynamic displacement in the flexible crankshaft was validated using another case study based on fatigue analysis of the crankshaft showing a relative error of 9%, which is less than that the relative error in Newman's model of diesel engine fuel consumption and Lansky's model of diesel engine cylinders. The paper also presents a proposed approach of fatigue failure analysis for vehicular dynamic components and presents a proposed nanostructure of crankshafts for improving such fatigue performance. The developed models would help develop efficient diesel engines and help prolong their service life. [ABSTRACT FROM AUTHOR] more...

This article investigates the mechanical reliability benefits of carbon nanotube (CNT) off-chip interconnects for future electronic packages. Finite-element analysis (FEA) of a silicon chip attached to an organic substrate showed that CNT off-chip interconnects with an isotropic modulus of 1 MPa reduced the principal stresses in the silicon chip ~71%–93% compared with lead-free solder balls without underfill. In addition to reducing chip stresses, chip warpage was essentially eliminated by utilizing CNT interconnects compared with solder balls. Parameters of importance for the implementation of CNTs as interconnects such as CNT modulus and height were investigated with finite-element analysis. It was found that chip stresses increase with increasing CNT modulus, but for the modulus range reported in the literature and examined here (0.1–500 MPa), chip stresses were much less than packages utilizing solder balls. Due to the structure and morphology of CNT forests, the different material model types of fully isotropic versus transversely isotropic that can be used to model CNT interconnects were investigated. While the models yielded similar mechanical behavior in the finite-element analyses, the isotropic CNT model was mechanically conservative and simpler to implement and, therefore, sufficient for future thermomechanical reliability studies. To further demonstrate the thermomechanical reliability benefits, silicon chips with CNT off-chip interconnects were fabricated and assembled to organic substrates and subjected to cyclic thermal shock testing. During testing, the daisy chain circuit containing CNT interconnects survived 1660 cycles, demonstrating that CNT interconnects mechanically decouple the chip from the substrate and, therefore, reduce chip stresses caused by coefficient of thermal expansion (CTE) mismatch. [ABSTRACT FROM AUTHOR] more...

Wood and composites cantilever beam structure has gained attention among researchers in the current years due to its universal structural applications, such as bridges, aeroplane wings, buildings, and transmission towers. However, when the structure is exposed to a constant loading for a very long time, it induces a structural collapse due to creep deformation. Therefore, it is essential to understand and identify the initial creep that can lead to structural collapse. In this study, wood and composite materials exhibit the same structural material morphology which performs as anisotropic material as it majorly contributes to failure. In this study, a state-of-the-art review of creep analysis and engineering design is carried out, with particular emphasis on the creep methodology of a cantilever beam. The existing theories and creep design approaches are grouped into two analysis methods, namely experimental and numerical approaches. To be more specific, the experimental works involved two main methods, namely load-based (conventional) and temperature-based (accelerated) techniques. Selected creep test on cantilever beam structure and coupon scale of wood and composite were highlighted and proposed as the building blocks for a prospective structural creep methodology. These aids build confidence in the underlying methods while guiding future work and areas, especially for long-term service of full-scale structure. At the end, the challenges of creep behaviour description accuracy and improvement on the strength criteria in engineering design were presented. more...

A novel laboratory diffractometer for time‐resolved high‐resolution X‐ray diffraction studies of reversible and irreversible processes in crystalline materials under uniaxial compression and vibration is described. Temporal resolution up to milliseconds for double‐crystal and up to tens of seconds for triple‐crystal diffraction experiments was achieved with a single adaptive bending X‐ray optics element. Design solutions and techniques for applying and controlling uniaxial compression and vibration for in situ time‐resolved studies are described. Results are presented for various static and dynamic load experiments, controlled by a system based on the TANGO Controls framework. Rocking curves of paratellurite (TeO2) under quasi‐static compression and lithium fluoride (LiF) under ultrasonic vibration were measured with temporal resolution. Reciprocal‐space maps of LiF under static compression and quartz (SiO2) under ultrasonic vibration were collected. [ABSTRACT FROM AUTHOR] more...

An inductive-deductive-inductive (I-D-I pedagogical approach, strengthened with physical model representation (PMR) was taken in a mechanics of materials course. The first inductive phase consisted of visualization and experimentation with a simple physical model. The second inductive phase consisted of problem solving and physical model development. The two inductive phases were bridged with a more deductive development of the constitutive equations. The implementation of this approach in a course that previously only used lecture resulted in a significant increase in the student passing rate and decrease in the number of withdrawals. The importance of the three phases and the physical representation is discussed. more...

Hardness is one of the most important mechanical properties of materials, since it is used to estimate their quality and to determine their suitability for a particular application. One method of determining quality is the Vickers hardness test, in which the resistance to plastic deformation at the surface of the material is measured after applying force with an indenter. The hardness is measured from the sample image, which is a tedious, time-consuming, and prone to human error procedure. Therefore, in this work, a new automatic method based on image processing techniques is proposed, allowing for obtaining results quickly and more accurately even with high irregularities in the indentation mark. For the development and validation of the method, a set of microscopy images of samples indented with applied forces of 5N and 10N on AISI D2 steel with and without quenching, tempering heat treatment and samples coated with titanium niobium nitride (TiNbN) was used. The proposed method was implemented as a plugin of the ImageJ program, allowing for obtaining reproducible Vickers hardness results in an average time of 2.05 seconds with an accuracy of 98.3% and a maximum error of 4.5% with respect to the values obtained manually, used as a golden standard. more...

Summary: The effects of solvent absorption on the electrochemical and mechanical properties of polymer electrolytes for use in solid-state batteries have been measured by researchers since the 1980s. These studies have shown that small amounts of absorbed solvent may increase ion mobility and decrease crystallinity in these materials. Even though many polymers and lithium salts are hygroscopic, the solvent content of these materials is rarely reported. As ppm-level solvent content may have important consequences for the lithium conductivity and crystallinity of these electrolytes, more widespread reporting is recommended. Here we illustrate that ppm-level solvent content can significantly increase ion mobility, and therefore the reported performance, in solid polymer electrolytes. Additionally, the impact of absorbed solvents on other battery components has not been widely investigated in all-solid-state battery systems. Therefore, comparisons will be made with systems that use liquid electrolytes to better understand the consequences of absorbed solvents on electrode performance. more...