A simplified nonlinear model for bamboo-reinforced concrete beams based on lumped damage mechanics

Bamboo’s renewability may justify bamboo-reinforced concrete (BRC) structures. For practical applications, the accurate description of BRC flexural behaviour is paramount. Lumped damage mechanics is an interesting alternative among some possibilities on nonlinear models since it is based on key concepts of classic fracture and damage mechanics. Therefore, this paper presents a novel lumped damage model for BRC beams. The model’s accuracy is tested with experiments found in the technical literature. Regarding the analysed experiments, the proposed model presents well-fitted results. Finally, the proposed model is feasible for practical applications, even considering structural reliability analysis like Monte Carlo, since it is easy to implement and presents low computational effort

Experimental test on 3D-printing components for Architectural Restoration

The paper investigates the use of 3D-printed components made from Polylactic Acid (PLA) for the restoration of architectural and ornamental elements, focusing on architectural/structural components. The material PLA was chosen for its potentiality in respecting the principles of restoration, recognizability, reversibility and minimum intervention, thanks its visual appearance, very different from typical construction materials, biodegradability and affordability. The paper represents an exploratory study aimed to derive the characteristics of 3D-printed PLA components thought tensile tests on dog-bone samples, and to analyze the behavior of structural components, thought tensile and bending tests on small truss beam samples. Unlike previous works mainly oriented towards aesthetic reproduction, this study focuses on the mechanical performance of PLA components designed for structural integration in restoration projects. The results show that the 3D-printed PLA components exhibit an average tensile strength of 44 MPa and an average Young’s modulus of 1270 MPa, values consistent with literature for fully dense PLA prints, and peak loads of about 6.4 kN in tension and 5 kN in bending for truss elements. Furthermore, this study provides data useful for future numerical modelling of 3D-printed structural elements in PLA, aimed at predicting their structural performance and supporting the design phase

Damage of additively manufactured polymer materials: experimental and probabilistic analysis

This paper presents a study on the tensile, fracture, damage, and reliability properties of 3D printed polylactic acid (PLA), based on a series of experiments. The study focuses on polylactic acid (PLA) samples produced using fused filament manufacturing (FFF) technology, specifically examining unidirectional print orientations of 0°, 45°, and 90°. Tensile testing demonstrated significant anisotropy in mechanical behavior, The specimens oriented at 0° exhibited the highest tensile strength, while those at 90° showed the lowest. An increase in artificial crack length (a) resulted in a progressive decrease in the mechanical properties. Weibull analysis confirmed the presence of significant anisotropic behavior in 3D-printed PLA specimens, with ultimate stress (σu0) values ranging from 39.82 MPa for the 90° orientation to 44.69 MPa for the 0° orientation, and elastic stress (σe0) values from 35.49 MPa (90°) to 39.11 MPa (0°), indicating greater strength for the 0° oriented specimens. Damage evolution analysis showed accelerated damage, with the 90° orientation demonstrating the fastest rate of damage compared to the 0° and 45° orientations. This indicates that the 90° orientation is more vulnerable to crack propagation and has diminished structural integrity under stress

An experimental study into the net cross-sectional failure of damaged plates with holes for different steel grades and temperatures

This study reports an experimental investigation on the applicability of the net cross-sectional resistance rules of Eurocode 3 for steel plates with different bolt-hole configurations and steel grades, when relatively small fatigue cracks are present at the edge(s) of the holes. Previous studies have confirmed that the considered design rule is on the safe side. Moreover, part of this safety margin accounts for the potential occurrence of relatively small fatigue cracks. Two steel grades are considered, namely S275JR and S700MC. Therefore, in addition to previous studies, a relatively high steel grade is considered. Moreover, some tests were carried out on cooled specimens to get an impression of the effect of low temperatures on the failure mechanism.  The experimental results demonstrate that relatively small cracks (<1 mm) have a negligible practical influence on the measured ultimate resistance of the plates. Furthermore, the failure assessment diagram is found to be suitable to predict the critical condition in the presence of cracks with length and shape as found in the experiments, also for relatively high steel grades

A novel approach to estimation of residual strength of laminated polymer composites under compression after impact

This work is dedicated to the experimental study of the influence of preliminary dynamic loading on the residual strength of the laminated polymer composite under compression. A series of low-velocity transverse drop-weight impact tests in a wide range of energies was carried out, followed by quasi-static compression of composite specimens with two reinforcement schemes [0/90]n and [±45]n. Nonlinearity of the obtained dependences of residual static strength on the energy of preliminary dynamic loading has been discovered. It has been noted that there are three characteristic stages on the diagram of fiberglass laminate’s impact sensitivity: area of impact insensitivity; area of reduced bearing capacity; area of achieving the minimum bearing capacity. The identified patterns are consistent with the data on the response of specimens during impact, as well as with specimens’ surface damage after dynamic loading. An anisotropy of the composite's impact sensitivity has been discovered. A novel approach to estimation of residual strength of laminated polymer composites under compression after impact and determination of impact sensitivity thresholds based on the use of mathematical models has been proposed. A new model of residual strength has been developed and tested, its applicability for description of the mechanical behavior of composites with various reinforcement schemes has been demonstrated

Effect of contact geometry, loading, material properties and relative slip on the fretting fatigue behaviour of metallic components

Metallic structural components, placed in contact with other bodies while experiencing vibrations in operating conditions, are susceptible to fretting, which can have a significant impact on their fatigue performance. Although extensive research has been conducted over the past decades to analyze the effects of various fretting influencing factors (including loading conditions, friction coefficient, relative slip amplitude, contact configuration, surface finishing, material properties, and environmental factors), this area of study remains an active field of investigation. In this paper, an experimental campaign reported in the literature, involving Al-4Cu specimens subjected to a partial slip regime cylindrical fretting contact, is examined by means of an analytical methodology developed by the authors. The results obtained through the proposed methodology demonstrate good agreement with the experimental observations in terms of both fatigue life and crack propagation direction. Furthermore, a parametric analysis is carried out to assess the role of different parameters in influencing the fretting fatigue behaviour, providing valuable insights into their effects on crack orientation and component durability

Studying the fracture surface of brass CuZn37 and aluminum 1100 and their relationship with formability in Single Point Incremental Forming

Single Point Incremental Forming was conducted on Aluminum1100 and Brass CuZn37 to form a hyperbolic truncated pyramid with varying wall angles until the fracture occurs. The formability of the specimens in terms of fracture depth and maximum wall angle was measured; and scanning electron microscopic photography was used to capture the fractured surface of the specimens to perform a fractography analysis. In each specimen's fracture surface, the identification of the voids shape, calculation of the void volume fraction (VVF) and void size, and the classification of the voids have been performed to allow for the identification of the relationship between formability and the microstructure of both materials. Also, the effect of the input parameters on this relationship has been identified. The results showed that when the VVF and the average void size in the fractured surface increase, the formability of the material increases.  And that the optimal SPIF conditions that increase void volume fraction and formability in CuZn37 occur when all input parameters are set to medium levels. For aluminum 1100, the optimal conditions have a low level of feed rate, a high level of tool speed and sheet thickness, and a medium level of tool diameter and step size

Study on B4C Particulates Size on Mechanical Behavior, Fractured Surface and Optimization of the Wear Parameters of the Al7075 Composites by Statistical Approach

Aluminum composites with varied weight percentages of 0-2.5 B4C particles and micro- and nanoparticle sizes were fabricated by stir-casting. The material's mechanical and wear characteristics were evaluated. We used dry pin-on-disc wear testing to examine the wear behavior of both micro and nano composites. In the sliding wear trials, different particle sizes (micro and nano), sliding distances (1500 m and 3000 m), and sliding speeds (3 m/s and 6 m/s) were employed. Scanning Electron Microscope (SEM) was utilized in the experiment to examine the materials and microstructures of several composites. Uniform dispersion of the micro and nano particles was readily evident in the SEM image. B4C particle microhardness increased by 16.06 % in nano composites and 10.78 % in micro composites. In a similar way, B4C particles' tensile strength increased by 12.90% in nano composites and 8.78% in micro composites. Taguchi design for experimental technique was applied to a L8 orthogonal array in order to design and ascertain the effects of sliding distance, sliding speed, and particle size on dry sliding wear behavior. ANOVA study showed that the most significant influencing factor on wear resistance was particle size (61.29%), followed by sliding speed (17.27%) as well as sliding distance (14.20%). From the confirmatory tests, the Coefficient of Friction (COF) of the produced composites had a maximum error of 9.09 % and the error of 3.33 % was found in the wear rate which was within the acceptable limit. The wornout surface shows that the composite reinforced with nanoparticles has a smooth wear surface with a finer wear scar

A digital twin framework with MobileNetV2 for damage detection in slab structures

In this study, a digital twin framework is proposed for damage detection in a civil structure, which consists of a finite element model, neural networks, model updating methods, and signal processing. To verify the proposed framework, we present a case study of slab structure using deflection measurement as input data. The dynamic characteristics of the physical model are used to calibrate the digital twin model. Damage scenarios are created on the digital twin model. The defection of the damaged slab under static loads is analyzed with two-dimensional discrete wavelet theory (DWT), whereas the diagonal wavelets are used to extract images data set used to train the convolutional neural network (CNN). MobileNetV2 uses transfer learning can reduce the number of trained parameters and hence perform fast convergence. The proposed method gives high accuracy about detection of low-severity damage having the severity less than 10%. There is more than 80% accuracy for predicting the damaged location and its severity. The success of using MobileNetV2 and transfer learning helps to improve the methods further on mobile devices and the potential for more applications. Moreover, the proposed framework does not require the data of the intact structures, leading to much wider applications

Comparative assessment of the acoustic activity and the Pressure Stimulated Voltage in marble specimens under compression

The temporal evolution of the electric activity generated in marble specimens under uniaxial compression is analyzed and quantified in terms of the Pressure Stimulated Voltage (Electric Potential) developed. The evolution of the electric activity is considered in juxtaposition to that of the respective acoustic one, quantified either in terms of the average frequency of generation of acoustic signals or of their Cumulative Energy content. Two classes of specimens were tested, differing with respect to the loading rate imposed. It is concluded that the electric activity is very weak, or even negligible, until the critical instant designated by the entrance into the stage of thermodynamically irreversible response of the material. Beyond this instant the electric activity starts increasing very rapidly almost until the instant at which the load attains its peak value. A few seconds before fracture, the electric signal exhibits an abrupt drop. The temporal evolution of the electric activity and that of the acoustic one are in excellent agreement, independently of the parameter used for their quantification. The study revealed that both activities provide clear pre-failure indices, early warning about upcoming disastrous fracture. Moreover, it was highlighted that the loading rate diversifies the results only from a quantitative point of view, “translating” the stress interval within which the pre-failure indices are located: The higher the loading rate the lower the stress level at which the pre-failure indices are detected