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1 – 10 of 919
Article
Publication date: 21 February 2024

Mohan Kumar K and Arumaikkannu G

The purpose of this paper is to compare the influence of relative density (RD) and strain rates on failure mechanism and specific energy absorption (SEA) of polyamide lattices…

Abstract

Purpose

The purpose of this paper is to compare the influence of relative density (RD) and strain rates on failure mechanism and specific energy absorption (SEA) of polyamide lattices ranging from bending to stretch-dominated structures using selective laser sintering (SLS).

Design/methodology/approach

Three bending and two stretch-dominated unit cells were selected based on the Maxwell stability criterion. Lattices were designed with three RD and fabricated by SLS technique using PA12 material. Quasi-static compression tests with three strain rates were carried out using Taguchi's L9 experiments. The lattice compressive behaviour was verified with the Gibson–Ashby analytical model.

Findings

It has been observed that RD and strain rates played a vital role in lattice compressive properties by controlling failure mechanisms, resulting in distinct post-yielding responses as fluctuating and stable hardening in the plateau region. Analysis of variance (ANOVA) displayed the significant impact of RD and emphasised dissimilar influences of strain rate that vary to cell topology. Bending-dominated lattices showed better compressive properties than stretch-dominated lattices. The interesting observation is that stretch-dominated lattices with over-stiff topology exhibited less compressive properties contrary to the Maxwell stability criterion, whereas strain rate has less influence on the SEA of face-centered and body-centered cubic unit cells with vertical and horizontal struts (FBCCXYZ).

Practical implications

This comparative study is expected to provide new prospects for designing end-user parts that undergo various impact conditions like automotive bumpers and evolving techniques like hybrid and functionally graded lattices.

Originality/value

To the best of the authors' knowledge, this is the first work that relates the strain rate with compressive properties and also highlights the lattice behaviour transformation from ductile to brittle while the increase of RD and strain rate analytically using the Gibson–Ashby analytical model.

Details

Rapid Prototyping Journal, vol. ahead-of-print no. ahead-of-print
Type: Research Article
ISSN: 1355-2546

Keywords

Article
Publication date: 15 January 2024

Mohammad A Gharaibeh, Markus Feisst and Jürgen Wilde

This paper aims to present two Anand’s model parameter sets for the multilayer silver–tin (AgSn) transient liquid phase (TLP) foils.

Abstract

Purpose

This paper aims to present two Anand’s model parameter sets for the multilayer silver–tin (AgSn) transient liquid phase (TLP) foils.

Design/methodology/approach

The AgSn TLP test samples are manufactured using pre-defined optimized TLP bonding process parameters. Consequently, tensile and creep tests are conducted at various loading temperatures to generate stress–strain and creep data to accurately determine the elastic properties and two sets of Anand model creep coefficients. The resultant tensile- and creep-based constitutive models are subsequently used in extensive finite element simulations to precisely survey the mechanical response of the AgSn TLP bonds in power electronics due to different thermal loads.

Findings

The response of both models is thoroughly addressed in terms of stress–strain relationships, inelastic strain energy densities and equivalent plastic strains. The simulation results revealed that the testing conditions and parameters can significantly influence the values of the fitted Anand coefficients and consequently affect the resultant FEA-computed mechanical response of the TLP bonds. Therefore, this paper suggests that extreme care has to be taken when planning experiments for the estimation of creep parameters of the AgSn TLP joints.

Originality/value

In literature, there is no constitutive modeling data on the AgSn TLP bonds.

Details

Soldering & Surface Mount Technology, vol. 36 no. 2
Type: Research Article
ISSN: 0954-0911

Keywords

Article
Publication date: 9 January 2024

Yunfei Zou

This study aims to enhance the understanding of fiber-reinforced polymer (FRP) applications in partially confined concrete, with a specific focus on improving economic value and…

Abstract

Purpose

This study aims to enhance the understanding of fiber-reinforced polymer (FRP) applications in partially confined concrete, with a specific focus on improving economic value and load-bearing capacity. The research addresses the need for a more comprehensive analysis of non-uniform vertical strain responses and precise stress–strain models for FRP partially confined concrete.

Design/methodology/approach

DIC and strain gauges were employed to gather data during axial compression tests on FRP partially confined concrete specimens. Finite element analysis using ABAQUS was utilized to model partial confinement concrete with various constraint area ratios, ranging from 0 to 1. Experimental findings and simulation results were compared to refine and validate the stress–strain model.

Findings

The experimental results revealed that specimens exhibited strain responses characterized by either hardening or softening in both vertical and horizontal directions. The finite element analysis accurately reflected the relationship between surface constraint forces and axial strains in the x, y and z axes under different constraint area ratios. A proposed stress–strain model demonstrated high predictive accuracy for FRP partially confined concrete columns.

Practical implications

The stress–strain curves of partially confined concrete, based on Teng's foundation model for fully confined stress–strain behavior, exhibit a high level of predictive accuracy. These findings enhance the understanding of the mechanical behavior of partially confined concrete specimens, which is crucial for designing and assessing FRP confined concrete structures.

Originality/value

This research introduces innovative insights into the superior convenience and efficiency of partial wrapping strategies in the rehabilitation of beam-column joints, surpassing traditional full confinement methods. The study contributes methodological innovation by refining stress–strain models specifically for partially confined concrete, addressing the limitations of existing models. The combination of experimental and simulated assessments using DIC and FEM technologies provides robust empirical evidence, advancing the understanding and optimization of FRP-concrete structure performance. This work holds significance for the broader field of concrete structure reinforcement.

Details

International Journal of Structural Integrity, vol. ahead-of-print no. ahead-of-print
Type: Research Article
ISSN: 1757-9864

Keywords

Article
Publication date: 25 January 2024

Shrushti Maheshwari, Zafar Alam and Sarthak S. Singh

The purpose of this study is to experimentally investigate the large deformation compression characteristics of fused deposition modelling (FDM)-printed poly lactic acid (PLA)…

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Abstract

Purpose

The purpose of this study is to experimentally investigate the large deformation compression characteristics of fused deposition modelling (FDM)-printed poly lactic acid (PLA), considering the combined effect of infill density and strain rate, and to develop a constitutive viscoplastic model that can incorporate the infill density to predict the experimental result.

Design/methodology/approach

The experimental approach focuses on strain rate-dependent (2.1 × 10−4, 2.1 × 10−3, and 2.1 × 10−2 s−1) compression testing for varied infill densities. Scanning electron microscopy (SEM) imaging of compressed materials is used to investigate deformation processes. A hyperelastic-viscoplastic constitutive model is constructed that can predict mechanical deformations at different strain rates and infill densities.

Findings

The yield stress of PLA increased with increase in strain rate and infill density. However, higher degree of strain-softening response was witnessed for the strain rate corresponding to 2.1 × 10−2 s−1. While filament splitting and twisting were identified as the damage mechanisms at higher strain rates, matrix crazing was observed as the primary deformation mechanism for higher infill density (95%). The developed constitutive model captured yield stress and post-yield softening behaviour of FDM build PLA samples with a high R2 value of 0.99.

Originality/value

This paper addresses the need to analyse and predict the mechanical response of FDM print polymers (PLA) undergoing extensive strain-compressive loading through a hyperelastic-viscoplastic constitutive model. This study links combined effects of the printing parameter (infill density) with the experimental parameter (strain rate).

Article
Publication date: 21 November 2023

Diab M. Al-Badayneh, Anis Ben Brik and Amr Elwakad

This study aims to examine social determinants and social strains of cyberbullying victimization among expatriate populations in high-income countries such as Qatar. The authors…

Abstract

Purpose

This study aims to examine social determinants and social strains of cyberbullying victimization among expatriate populations in high-income countries such as Qatar. The authors argue that expatriate students will be exposed to stains and pressures due to several factors, such as feeling alienated, lonely, homesick, insecure and helpless. This study examines a partial assumption of general strain theory (GST), which posits that expats’ cyberbullying victimization can create negative stimuli that lead to negative feelings and, as a result, to delinquent behavior. The delinquent behavior can be seen as a coping method in encountering strains. Logistic regression analysis is applied (using SPSS v. 21) to test the hypothesis that the victimization of expats’ cyberbullying could lead to strain and delinquency.

Design/methodology/approach

A sample of 2,428 expatriate students (46% males and 54% females) was randomly selected from seven public schools in Qatar. The average number of siblings in the household was 2.7. Around 10.8% of the sample reported victimization by cyberbullying. Most came from intact families (80.6%) compared to 19.4 living in broken homes. Concerning the birth order of the student in the family, 25% of the sample were firstborn, and 20% were middle-born. Students’ mother relationships were higher than students’ father relationships (69% vs 51%, respectively). Fathers were higher in undergraduate education than mothers (60% vs 49%, respectively). Considering that 58% of women did not have a job, most fathers work in administrative positions (47% in administrative work and 39% in professional positions) as opposed to mothers’ positions (15% and 21%, respectively). The survey was distributed among expatriate students by trained researchers, teachers and social workers in public schools. The researchers explained the purpose of the study, confidentiality and potential risks and provided directions for completing the survey. Parents and their children provided signed informed consent before participation, following the institutional review boards of Qatar University’s Human Subject Research Committee and the Ministry of Social Development. The victimization of cyberbullying is measured at the dichotomy level by asking a general cyberbullying question (In the last 12 months, had you been bullied by other students using mobile messages, email, voice or video messages? Responses were 1 – yes and 0 – no). A definition of cyberbullying was included in the questionnaire. Independent measures are as follows: (1) demographic variables: gender, belief, health, number of friends and exposure to violence; (2) family variables: delinquent family, coercive parenting, family relations, family disputes, father absence and family ties; (3) school variables: school satisfaction, school violence, student fighting, teachers' violence, school truancy and going late to school; (4) imprudent behavior: smoking, alcohol, not using a seat belt, gambling, stealing less than 100 QR, chewing tobacco, stimuli, volatile drugs, sexual harassment, throwing garbage out of the car, cheating, vandalism and victimization.

Findings

Findings showed that n = 255, 10.8% of the expats’ sample N = 2,428 reported victimization of cyberbullying, of whom 46% were males and 54% were females. A total of 24% of the victims of cyberbullying were males, and 5.8% were females. About a third of the sample were cyberbullying perpetrators (n = 716, 29.5%). Victims of cyberbullying came from intact families (62.4%) compared to broken families (37.6%). A round third of the victims reported the absence of a father during their childhood (n = 78, 31.7%). Most of the victims came from a typical community compared to the delinquent community (71.2% vs 28.2%). About a third of the victims reported it was easy to talk with the father when needed (32% compared to 42.7%), who said it was easy. More than half of the victims do not use seat belts. A low percentage of them were gambling (n = 68, 27% or 2.9% of the total sample). Regarding escaping imprudent and delinquent behaviors, findings showed that a third and more than a tenth of the cyberbullying were smokers and alcoholics (n = 69, 27.4% and n = 42, 16.7% respectively). Moreover, among the most serious, widely spread student problems, around a quarter of the victims reported using chewing tobacco (Sweeka is the local name) (n = 54, 21.4%). Finally, drug use among victims was more than a tenth of them (n = 41, 16.3%). About a quarter of the victims reported stealing less than 100 QR (n = 67, 26.8% or 2.9% of the total sample). Concerning the crimes committed by victims, findings showed that more than forth of them committed assault (n = 71, 28.3%), student fights (n = 202, 80.8%), school violence (n = 117, 46.6%) and half of the victims (50.2%) were also victims of face-to-face bullying. Little below half of the sample was exposed to violence (n = 120, 48.6%) and was the victim of violence in the past 12 months (n = 100, 40.8%). A significant gender differences was found in the victimization of cyberbullying (1 = yes, 0 = no) (a = 000). Moreover, significant mean differences were found between expatriates student victimization of cyberbullying at (a = 000) in all strain variables. Using binary regression analysis to examine the equality of probability of being a victim of cyberbullying as accounted for by the independent variables, the model’s predictability was 89.4%. The Hosmer and Lemeshow test and omnibus tests support the model’s fit (a = 000). Nagelkerke R2 shows that the stain variables accounted for 24% of the variance in the expat's student victimization of cyberbullying.

Research limitations/implications

Conceptualization and determination of what constitutes cyberbullying from the criminal law perspective are needed. Cyberbullying is defined as a form of violence and crime involving new technologies (Sun et al., 2016, p. 62). Policymakers should provide accessible and equitable access to the criminal justice system, the integration of expatriates and the provision of support services to avoid delinquency.

Practical implications

A social cohesion, inclusion and well-being policy is needed for expatriate students and their families in Qatar. In particular, cultural diversity policy and programs, a source of strength and enrichment should be promoted in educational settings. Social inclusion and cultural diversity programs could ease the alienation and marginalization that expatriate students may encounter in their host societies to prevent stains and negative emotions that lead to delinquency and criminal behaviors. Access to support services without discrimination to avoid health and psychological strains and risk factors. This includes but is not limited to avoidance of stigmatization, embarrassment, sense of helplessness, humiliation and other negative feelings toward expatriates. Awareness and promotion of cultural diversity values are needed to enhance cultural acceptance to reduce victimization among the expatriate population. Criminal law and security implications conceptualization and determination of what constitutes cyberbullying from the criminal law perspective are needed. Cyberbullying is a form of violence and crime involving new technologies (Sun et al., 2016). Policymakers should provide accessible and equitable access to the criminal justice system, integrating expatriates and providing support services to avoid delinquency. There is a pressing need for further research within the realm of crime and law to establish the precise legal boundaries surrounding cyberbullying and to delineate the potential scope for legislative measures aimed at safeguarding against victimization in Qatar. Although the state of Qatar has taken steps to address cyberbullying by incorporating it into relevant legal frameworks, there remains a gap in terms of specifically targeting cyberbullying involving children and adolescents. Despite the introduction of the new Cybercrime Prevention Law, the issue of cyberbullying among these vulnerable groups is not adequately addressed.

Social implications

Social implication includes but is not limited to avoidance of stigmatization, embarrassment, sense of helplessness, humiliation and other negative feelings towards expatriate. Awareness and promotion of cultural diversity values is needed to enhance cultural acceptance to reduce victimization among expatriate population.

Originality/value

The present study examines some strain theory assumptions and the victimization of the cyberbullying expatriate population. This study tests a partial assumption of GST, which states that the expatriate population’s exposure to the victimization of cyberbullying can lead to negative stimuli that, in return, create negative feelings and, as a result, imprudent and delinquent behavior. The cyberbullying behavior can be seen as an escaping and coping method in encountering strains. This study underscores the presence of cyberbullying within high schools among expatriate students, exerting significant effects on their personal, social and emotional behaviors. The novel insights gleaned from this investigation contribute substantively to the comprehension of both the pervasiveness and repercussions of cyberbullying on the well-being of expatriate students. This contribution is particularly vital, given the dearth of research in the field, largely attributable to the growing dependence of students on the internet for various cyber activities. This study examines a partial assumption of GST (in non-Western country). Moreover, it uses an advanced statistical analysis and large sample.

Details

Journal of Criminological Research, Policy and Practice, vol. 10 no. 1
Type: Research Article
ISSN: 2056-3841

Keywords

Article
Publication date: 20 June 2023

Kei Kimura, Takeshi Onogi and Fuminobu Ozaki

This work examines the effects of strain rate on the effective yield strength of high-strength steel at elevated temperatures, through tensile coupon tests at various strain…

Abstract

Purpose

This work examines the effects of strain rate on the effective yield strength of high-strength steel at elevated temperatures, through tensile coupon tests at various strain rates, to propose appropriate reduction factors considering the strain rate effect.

Design/methodology/approach

The stress–strain relationships of 385 N/mm2, 440 N/mm2 and 630 N/mm2-class steel plates at elevated temperatures are examined at three strain rate values (0.3%/min, 3.0%/min and 7.5%/min), and the reduction factors for the effective yield strength at elevated temperatures are evaluated from the results. A differential evolution-based optimization is used to produce the reduction-factor curves.

Findings

The strain rate effect enhances with an increase in the standard design value of the yield point. The effective yield strength and standard design value of the yield point exhibit high linearity between 600 and 700 °C. In addition to effectively evaluating the test results, the proposed reduction-factor curves can also help determine the ultimate strength of a steel member at collapse.

Originality/value

The novelty of this study is the quantitative evaluation of the relationship between the standard design value of yield point at ambient temperature and the strain-rate effect at elevated temperatures. It has been observed that the effect of the strain rate at elevated temperatures increases with the increase in the standard design value of the yield point for various steel strength grades.

Details

Journal of Structural Fire Engineering, vol. 15 no. 1
Type: Research Article
ISSN: 2040-2317

Keywords

Article
Publication date: 24 May 2022

Florence YY Ling and Elsie Kai Ying Mok

This study aims to investigate how to manage the stressors that facility managers (FMs) face with the aim of reducing their stress and strain levels.

Abstract

Purpose

This study aims to investigate how to manage the stressors that facility managers (FMs) face with the aim of reducing their stress and strain levels.

Design/methodology/approach

Using the job demands-resources (JD-R) model, stressors are operationalized from job demands, job resources and personal resources constructs. A structured questionnaire was used to collect data from FMs based in Singapore.

Findings

FMs have significantly high levels of stress, but they are able to manage this well. Job demands that cause stress and strain are those relating to insufficient time to complete the work and difficulties in handling the work. The lack of job resources in terms of lack of organizational support and inadequate stress mitigation programs are associated with high levels of stress and strain.

Research limitations/implications

The limitations are the relatively small sample size and absence of a database of FMs in Singapore, and correlation is not causation when determining the association between stressors and stress and strain.

Practical implications

Based on the recommendations, employers and FMs may manage the specific stressors identified so that FMs’ stress and strain levels are under control to enable them to work optimally.

Originality/value

This research discovered that the JD-R model is moderated by certain features of facilities management and FMs. When these features are present, FMs are predisposed to more stressors, and higher stress and strain. For the facilities management profession, the discovery is that there are significantly more job demands: for in-house FMs compared to those working for outsourced firms; for FMs who need to carry out estate and asset management, landlord activities and facility planning compared to FMs who focus on operations and maintenance; and for FMs who work longer than five days compared to those who work a five-day week.

Details

Journal of Facilities Management , vol. 22 no. 1
Type: Research Article
ISSN: 1472-5967

Keywords

Article
Publication date: 22 January 2024

Hao Chen, Lynda Jiwen Song, Wu Wei and Liang Wang

The purpose of this study is to test the mechanism of visionary leadership on subordinates' work withdrawal behavior through cognitive strain and psychological contract violation…

Abstract

Purpose

The purpose of this study is to test the mechanism of visionary leadership on subordinates' work withdrawal behavior through cognitive strain and psychological contract violation, and also to reveal the possible dark side of visionary leadership. The moderation effects of subordinates' facades of conformity and leader behavioral integrity in the cognition–affect dual-path process are also discussed.

Design/methodology/approach

This study conducted a three-wave longitudinal survey. The data were collected from 574 employees and their superiors in several Chinese enterprises. The authors used Mplus 7.4 and adopted a bootstrapping technique in the data analysis.

Findings

Visionary leadership has positive effects on cognitive strain and psychological contract violation; cognitive strain and psychological contract violation mediate the relationship between visionary leadership and work withdrawal behavior, respectively. Subordinates' facades of conformity and leader behavioral integrity moderate the positive effects of visionary leadership on cognitive strain and psychological contract violation, as well as the indirect effect of visionary leadership on subordinates' work withdrawal behavior through cognitive strain and psychological contract violation.

Originality/value

This study reveals the underlying mechanism of visionary leadership's negative impact on job outcome through the cognition and affective reaction of subordinates to visionary leadership, and broadens the scope of visionary leadership research. It also provides some practical suggestions on how to transmit the organizational vision effectively and reduce subordinates' work withdrawal behavior.

Details

Management Decision, vol. ahead-of-print no. ahead-of-print
Type: Research Article
ISSN: 0025-1747

Keywords

Article
Publication date: 10 October 2023

Pawan Bishnoi and Pankaj Chandna

This paper aims to optimize the single-point incremental forming process variables for realizing higher formability in Inconel 625 components and to plot the forming limit diagram…

Abstract

Purpose

This paper aims to optimize the single-point incremental forming process variables for realizing higher formability in Inconel 625 components and to plot the forming limit diagram for Inconel 625 aviation-grade superalloy.

Design/methodology/approach

The formability of Inconel 625 components has been measured in terms of major strain, minor strain and minimum sheet thickness. Response surface methodology with desirability function analysis has been used to achieve maximum formability. The finite element analysis has been conducted at optimal parametric setting.

Findings

The derived forming limit diagram proves that the maximum forming limit for Inconel 625 is 57.5° at the optimal parametric setting, achieved with desirability of 0.995. The outcomes of finite element analysis conducted at optimal parametric setting show excellent agreement with confirmation experiment results.

Practical implications

Inconel 625 superalloy is frequently used in aircraft and other high-performance applications for its superior strength.

Originality/value

It has been suggested that to enhance formability, higher tool rotation speed, minimum step-size, larger tooltip diameter and higher wall angle must be used. Wall angle is the governing parameter among all the parameters.

Details

Aircraft Engineering and Aerospace Technology, vol. 96 no. 1
Type: Research Article
ISSN: 1748-8842

Keywords

Article
Publication date: 18 March 2024

Lifeng Wang, Fei Yu, Ziwang Xiao and Qi Wang

When the reinforced concrete beams are reinforced by bonding steel plates to the bottom, excessive use of steel plates will make the reinforced concrete beams become…

Abstract

Purpose

When the reinforced concrete beams are reinforced by bonding steel plates to the bottom, excessive use of steel plates will make the reinforced concrete beams become super-reinforced beams, and there are security risks in the actual use of super-reinforced beams. In order to avoid the occurrence of this situation, the purpose of this paper is to study the calculation method of the maximum number of bonded steel plates to reinforce reinforced concrete beams.

Design/methodology/approach

First of all, when establishing the limit failure state of the reinforced member, this paper comprehensively considers the role of the tensile steel bar and steel plate and takes the load effect before reinforcement as the negative contribution of the maximum number of bonded steel plates that can be used for reinforcement. Through the definition of the equivalent tensile strength, equivalent elastic modulus and equivalent yield strain of the tensile steel bar and steel plate, a method to determine the relative limit compression zone height of the reinforced member is obtained. Second, based on the maximum ratio of (reinforcement + steel plate), the relative limit compression zone height and the equivalent tensile strength of the tensile steel bar and steel plate of the reinforced member, the calculation method of the maximum number of bonded steel plates is derived. Then, the static load test of the test beam is carried out and the corresponding numerical model is established, and the reliability of the numerical model is verified by comparison. Finally, the accuracy of the calculation method of the maximum number of bonded steel plates is proved by the numerical model.

Findings

The numerical simulation results show that when the steel plate width is 800 mm and the thickness is 1–4 mm, the reinforced concrete beam has a delayed yield platform when it reaches the limit state, and the failure mode conforms to the basic stress characteristics of the balanced-reinforced beam. When the steel plate thickness is 5–8 mm, the sudden failure occurs without obvious warning when the reinforced concrete beam reaches the limit state. The failure mode conforms to the basic mechanical characteristics of the super-reinforced beam failure, and the bending moment of the beam failure depends only on the compressive strength of the concrete. The results of the calculation and analysis show that the maximum number of bonded steel plates for reinforced concrete beams in this experiment is 3,487 mm2. When the width of the steel plate is 800 mm, the maximum thickness of the steel plate can be 4.36 mm. That is, when the thickness of the steel plate, the reinforced concrete beam is still the balanced-reinforced beam. When the thickness of the steel plate, the reinforced concrete beam will become a super-reinforced beam after reinforcement. The calculation results are in good agreement with the numerical simulation results, which proves the accuracy of the calculation method.

Originality/value

This paper presents a method for calculating the maximum number of steel plates attached to the bottom of reinforced concrete beams. First, based on the experimental research, the failure mode of reinforced concrete beams with different number of steel plates is simulated by the numerical model, and then the result of the calculation method is compared with the result of the numerical simulation to ensure the accuracy of the calculation method of the maximum number of bonded steel plates. And the study does not require a large number of experimental samples, which has a certain economy. The research result can be used to control the number of steel plates in similar reinforcement designs.

Details

International Journal of Structural Integrity, vol. ahead-of-print no. ahead-of-print
Type: Research Article
ISSN: 1757-9864

Keywords

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