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This study aims to comprehensively investigate the mixed-mode fracture behavior and mechanical properties of selective laser sintering (SLS) polyamide 12 (PA12) components, considering different build orientations and layer thicknesses. The primary objectives include the following. Conducting mixed-mode fracture and mechanical analyses on SLS PA12 parts. Investigating the influence of build orientation and layer thickness on the mechanical properties of SLS-printed components. Examining the fracture mechanisms of SLS-produced Arcan fracture and tensile specimens through experimental methods and finite element analyses.

The research used a combination of experimental techniques and numerical analyses. Tensile and Arcan fracture specimens were fabricated using the SLS process with varying build orientations (X, X–Y, Z) and layer thicknesses (0.1 mm, 0.2 mm). Mechanical properties, including tensile strength, modulus of elasticity and critical stress intensity factor, were quantified through experimental testing. Mixed-mode fracture tests were conducted using a specialized fixture, and finite element analyses using the J-integral method were performed to calculate fracture toughness. Scanning electron microscopy (SEM) was used for detailed morphological analysis of fractured surfaces.

The investigation revealed that the highest tensile properties were achieved in samples fabricated horizontally in the X orientation with a layer thickness of 0.1 mm. Additionally, parts manufactured with a layer thickness of 0.2 mm exhibited favorable mixed-mode fracture behavior. The results emphasize the significance of build orientation and layer thickness in influencing mechanical properties and fracture behavior. SEM analysis provided valuable insights into the failure mechanisms of SLS-produced PA12 components.

This study contributes to the field of additive manufacturing by providing a comprehensive analysis of the mixed-mode fracture behavior and mechanical properties of SLS-produced PA12 components. The investigation offers novel insights into the influence of build orientation and layer thickness on the performance of such components. The combination of experimental testing, numerical analyses and SEM morphological observations enhances the understanding of fracture behavior in additive manufacturing processes. The findings contribute to optimizing the design and manufacturing of high-quality PA12 components using SLS technology.

The purpose of this paper is to study theoretically the ability of the prestressed foam core composite sandwich Split Cantilever Beam (SCB) for generating mixed-mode II/III crack loading conditions (the mode II fracture was provided by prestressing the beam using imposed transverse displacements).

The concepts of linear-elastic fracture mechanics were used. The fracture behavior was studied in terms of the strain energy release rate. For this purpose, a three-dimensional finite element model of the prestressed sandwich SCB was developed. The virtual crack closure technique was applied in order to analyze the strain energy release rate mode components distribution along the crack front.

It was found that the distribution is non-symmetric. The analysis revealed that a wide mixed-mode II/III ratios range can be generated by varying the magnitude of the imposed transverse displacement. The influence of the sandwich core material on the mixed-mode II/III fracture behavior was investigated. For this purpose, three sandwich beam configurations with different rigid cellular foam core were simulated. It was found that the strain energy release rate decreases when the foam core density increases.

For the first time, a mixed-mode II/III fracture study of foam core composite sandwich beam is performed.

The purpose of this paper is to show that mixed methods applied sequentially provide sufficient knowledge of topics under study.

This paper conducted an analysis of a real case using descriptive statistical and regression techniques.

The present study proposes the use of the so-called “sequential mixed-modes” in survey-based market research. This technique is based on the successive application of different information collection techniques (face-to-face, telephone and internet-based surveys); it offers four fundamental advantages: increased coverage rate; higher response rate; lower costs; and greater cooperation.

In addition to the normal limitations associated with conclusions derived from case studies, the data collection was carried out in only one autonomous community (Spain) and focussed only on one theme.

Firstly, it was found that data collection through mixed sequential modes substantially increases response rates in online surveys. This is particularly important as, in recent years, data collection through the internet has become almost standard market research practice. Secondly, the sample that resulted from the joint use of the three data collection modes more accurately reflected the distinctive features of the universe under study. A third recommendation is that the use of internet-based self-administered surveys is especially promising with individuals with a higher level of education and among students.

The decrease in the response rate is one of the greatest challenges of survey-based market research, given its impact on sample representativeness. This paper addresses this problem and exposes the advantages of the sequential use of mixed modes in the collection of information.

El objetivo de la presente investigación es mostrar que los modos mixtos aplicados de manera secuencial ofrecen un conocimiento adecuado de los temas objeto de estudio.

Se realiza el análisis de un caso real mediante técnicas descriptivas y regresión.

Este trabajo presenta los denominados “modos mixtos secuenciales” en la investigación a través de encuestas. Esta técnica se basa en la aplicación sucesiva de diferentes herramientas de recogida de información (encuestas presenciales, telefónicas y por Internet) y ofrece cuatro ventajas fundamentales; (1) aumento de la tasa de cobertura; (2) mayor tasa de respuesta; (3) menores costes; y (4) mayor cooperación.

Además de las limitaciones normalmente asociadas a los estudios de caso, la recogida de información se redujo a una única comunidad autónoma (España) y un único tema.

En primer lugar, se observa que la recogida de información mediante modos mixtos secuenciales aumenta de manera sustancial la tasa de respuesta en las encuestas online. Esto es particularmente relevante en la situación actual, pues la utilización de Internet casi se ha convertido en un estándar en la investigación de mercados. En segundo lugar, la muestra final obtenida como resultado del uso de tres modos de recogida refleja de manera más ajustada las características distintivas de la población objeto de estudio. Una tercera implicación es que el uso de encuestas online de carácter autoadministrado es especialmente prometedor en individuos de mayor nivel educativo y entre estudiantes.

摘要

本文的目的是要证明，按顺序应用的混合方法为研究的主题提供了充分的知识。

本文运用描述性统计和回归技术对一个实际案例进行了分析。

本文提议使用 “顺序混合模式” 来调查市场研究。这项技术是基于连续运用不同的信息收集技术(面对面、电话和基于互联网的调查) ，它提供了四个基础性优势: 增加覆盖率; 更高的回复率; 降低成本; 和更大的协作。

除了常见的案例研究所存在的局限性之外，本文的数据收集仅在一个自治社区(西班牙)进行，并且只集中于一个主题。

首先，通过混合序列模式收集数据，大大提高了在线调查的回复率。这一点尤其重要，因为近年来，通过互联网收集数据几乎已成为标准的市场研究实践。其次，联合使用三种数据采集模式所得到的样本更准确地反映了所研究社区的鲜明特征。第三个建议是，使用基于互联网的自我管理调查对调查教育水平较高的个人和学生群体具有很大的调查前景。

回复率的下降是基于调查的市场研究面临的最大挑战之一， 因为它大大影响了样本代表性。本文解决了这一问题，并揭示了在信息收集中顺序使用混合模式的优点。

Wavelets are being increasingly used for damage diagnostics. The purpose of this paper is to present an algorithm that uses the wavelet transform for detecting mixed-mode, also known as combined mode, cracks in large truss structures.

The mixed-mode crack is modeled by superposing two damage modes, and this model is combined with a finite element model of the truss. The natural modes of the truss are processed through the wavelet transform and then used to determine the damage location. The influence of multiple parameters such as truss geometry, crack geometry, number of truss members, orientation of truss members, etc. is investigated as part of the study.

The proposed damage detection algorithm is found to be successful in detecting single mode as well as mixed-mode cracks even in the presence of significant end effects, and even when a relatively coarse sampling of natural modes is used. Results from multiple simulations that involve three commonly used truss structures are presented. A correlation between damage severity and the magnitude of wavelet coefficients is observed.

The proposed algorithm is found to be successful in accurately detecting damage, but direct determination of damage severity is found to be challenging.

This paper aims to achieve two main objectives. First, to introduce to the literature a new versatile active building block, namely, voltage differencing differential voltage current conveyor (VD-DVCC) for analog signal processing applications. Second, to design a novel electronically tunable mixed-mode universal filter. The designed filter provides low-pass, high-pass, band-pass, band-reject and all-pass responses in voltage-mode (VM), current-mode (CM), trans-impedance-mode (TIM) and trans-admittance-mode (TAM).

The proposed filter uses two VD-DVCCs, three resistors and two capacitors. All the capacitors used are grounded, which is advantageous from the monolithic integration point of view. The VD-DVCC is designed and validated in Cadence software using CMOS 0.18 µm process design kit from Silterra Malaysia at a supply voltage of ±1 V.

The proposed novel filter enjoys many attractive features including as follows: the ability to operate in all four modes, no requirement of capacitive matching, tunability of quality factor (Q) independent of pole frequency, availability of both inverting and non-inverting outputs for VM and TIM mode, high output impedance explicit current output for CM and TAM, no requirement for double/negative input signals (voltage/current) for response realization and low active and passive sensitivities. The filter is designed for a pole frequency of 5.305 MHz. The obtained results bear a close resemblance with the theoretical findings.

The proposed novel filter structure requires a minimum number of active and passive components and provides operation in all four operating modes. The filter will find application in structures of mixed-mode systems.

The purpose of this study is to explore an optimal research design for research on women entrepreneurs involved in negotiating term sheets for private equity capital. This research explores new ways for researchers to connect with such current “invisibles” through the use of a mixed method and mixed mode research design to expand sampling options and secure respondent participation. The authors discuss existing data sets that have been used as secondary sources for data on financing of companies and consider their inadequacy for research questions about process issues in negotiation. The authors present process-related findings regarding the efficacy of the research design.

This paper reviews research on research methodology, incorporating a discussion of practices outside of the entrepreneurship discipline to discover effective practices for identifying respondents and data not currently captured in entrepreneurship data sources. The respondents were found through social media sites, angel networks, University networks and via identification through a proprietary financial intelligence database.

An optimal research design to identify women business owners of growth-oriented firms who have negotiated private equity should consider mixed methods designs and mixed modes, including the use of digital networks that signal to potential respondents that research is being done.

Although the authors developed the multi-method, mixed mode (MMMM) research design, the sample size is still relatively small. This raises concerns about generalizability to the larger population and limits statistical analysis more suitable with larger data sets. However, the MMMM research design has enabled the authors to reach a difficult target sample. It has proven effective, although a longer time frame would have been helpful.

All of the large scale databases in entrepreneurship have limitations in providing optimal sampling frames for process-related research. The present research study was able to use conventional networks, social media sites and angel networks to connect with women business owners who have raised private equity, but who lack visibility in current data sets. The study shows that through the use of multiple methods, women entrepreneurs can be researched and some will share their experiences about process issues. The sample size was small and the quantitative data cannot be generalized. However, the methodology works and allows researchers to explore experiences that are not captured in existing data sets.

Entrepreneurship researchers can connect with “invisibles” by becoming more “social” and using social media sites that are used by women entrepreneurs. Researchers may not have immediate access to women entrepreneurs through these means, but rather they need to develop interpersonal contacts, build a social presence and trust to recruit respondents to complete online questionnaire studies about substantive topics such as negotiating term sheets for equity investments in their companies.

This paper summarizes the “research on research methodologies” in entrepreneurship, reviews secondary data sources and discusses their limitations for specific types of research questions. A review of the value of MMMM research designs and best practices in online survey research outside of entrepreneurship provides insights into the incorporation of digital tools in other disciplines.

The main aim of this study is to investigate the mixed-mode I/II failure and the cracking manner of three-dimensional (3D)-printed components made by the fused deposition modeling technique in an experimental and theoretical manner.

Acrylonitrile butadiene styrene (ABS) material and a modified printing method (that increases the adhesion and integrity between the layers and strands) are used for manufacturing the semicircular bending (SCB) test samples. In addition to precracking, the effect of additional stress concentration on the stress field is studied by introducing three small holes to the SCB fracture samples. The critical mixed-mode I/II failure loads obtained from the experiments are predicted using different stress/strain-based fracture theories, including maximum tangential stress (MTS), maximum tangential strain (MTSN), generalized form of MTS and MTSN and combination of them with equivalent material concept (EMC). The effects of plastic deformation, as well as the structural stress concentration, are considered for a more realistic prediction of mixed-mode fracture load.

The stress-based criteria are more suitable than the strain-based theories. Among the investigated fracture models, the EMC–generalized maximum tangential stress theory provided the best agreement with the experimental results obtained from 3D-printed SCB tests.

The influences of stress risers and applicability of different failure theories in cracked layered 3D-printed parts are studied on the fracture behavior of tested specimens under mixed-mode I/II.

The purpose of this study was to investigate the effects of CaCO₃ nanoparticles on the mechanical properties, and mixed-mode fracture behavior of acrylonitrile butadiene styrene 3D printed samples with different internal architectures.

The nanocomposite filaments have been fabricated by a melt-blending technique. The standard tensile, compact tension and special fracture test samples, named Arcan specimens, have been printed at constant extrusion parameters and at four different internal patterns. A special fixture was used to carry out the mixed-mode fracture tests of Arcan samples. Finite element analyses using the J-integral method were performed to calculate the fracture toughness of such samples. The fractographic observations were used to evaluate the mechanism of fracture at different concentrations of nanoparticles.

The addition of CaCO₃ nanoparticles has resulted in a significant increase in the fracture loading of the samples, although this increase was not consistent for all the filling patterns, being more significant for samples with linear and triangular structures. According to the fractographic observations, the creation of uniformly distributed microvoids due to the blunting effect of nanoparticles and 3D stress state at the crack tip in the samples with linear and triangular structures justify the enhancement in the fracture loading by the addition of CaCO₃ nanoparticles in the matrix.

There is a significant gap in the knowledge of the effects of different nanoparticles in the polymer samples produced by the fused filament fabrication process. One of such nanoparticles is an inorganic CaCO₃ nanoparticle that has been frequently used as nanofillers to improve the thermomechanical properties of thermoplastic polymers. Here, experimental and numerical studies have been conducted to investigate the effects of such nanoadditives on the mechanical and fracture behavior of 3D printed samples.

Acrylonitrile butadiene styrene (ABS), as a light and high strength thermoplastic polymer, has found extensive applications in different industries. Fused filament fabrication, known as three-dimensional (3D) printing technique is considered a rapid prototyping technique that is frequently applied for production of samples of ABS material. Therefore, the purpose of this study is to investigate the mechanical and fracture behavior of such materials and the techniques to improve such properties.

Experimental and numerical analyses have been conducted to investigate the effects of internal architecture and chopped carbon fiber (CF) fillers on the mechanical properties and mixed mode fracture behavior of the ABS samples made by 3D printing technique. Four different filling types at 70% filling ratios have been used to produce tensile and special fracture test samples with pure and CF filled ABS filaments (CF-ABS) using 3D process. A special fixture has been developed to apply mixed mode loading on fracture samples, and finite element analyses have been conducted to determine the geometric function of such samples at different loading angles.

It has been determined that the printing pattern has a significant effect on the mechanical properties of the sample. The addition of 15% CF to pure ABS resulted in a significant increase in tensile strength of 46.02% for line filling type and 15.04% for hexagon filling type. It has been determined that as the loading angle increases from 0° to 90°, the KIC value decreases. The addition of 15% CF increased the K_IC values for hexagonal and line filling type by 64.14% and 12.5%, respectively.

The damage that will occur in ABS samples produced in 3D printers depends on the type, amount, filling speed, filling type, filling ratio, filling direction and mechanical properties of the additives. All these features are clearly dependent on the production method. Even if the same additive is used, the production method difference shows different microstructural parameters, especially different mechanical properties.

An interface finite element for three‐dimensional problems based on the penalty method is presented. The proposed element can model joints/interfaces between solid finite elements and also includes the propagation of damage in pure mode I, pure mode II and mixed mode considering a softening relationship between the stresses and relative displacements. Two different contact conditions are considered: point‐to‐point constraint for closed points (not satisfying the failure criterion) and point‐to‐surface constraint for opened points. The performance of the element is tested under mode I, mode II and mixed mode loading conditions.