Spring Back Research Articles

Introduction: Sexism - A Problem With a Name

This special issue is premised on a claim: to make sexism the explicit object of academic enquiry is to generate new knowledge and understanding. To understand how sexism works, to ask why sexism remains stubbornly persistent in shaping worlds, determining possibilities, deciding futures, despite decades of feminist activism, is to work out and to work through the very mechanics of power. Sexism seems to operate as a well-oiled machine that runs all the more smoothly and efficiently for being in constant use. The effects of this constancy are wearing on those to whom sexism is directed. In this special issue we reflect on how and why sexism remains so persistent without isolating sexism from other machineries of power. We hope to intervene collectively in the reproduction of sexism, to throw a spanner in the works or even to become, to borrow Sarah Franklin's evocative phrase, a 'wench in the works'. It takes conscious willed effort not to reproduce sexism. (1) This special issue is part of this effort. WHY SEXISM? Why focus on sexism now? Why focus on sexism here? It might seem that I have already provided an answer to this question by acknowledging the persistence of sexism. As the contributions to this special issue explore, even if sexism seems like some tangible thing, knowable in and from its constancy, something we come up against, repeatedly, it is remarkably difficult to pin down. And that too is one of the reasons to focus on sexism: because so much of what we experience as sexism is dismissed as just what we experience. Focusing on sexism now and here matters because too often sexism is identified as either in the past tense (as what we dealt with, what we have overcome) or as elsewhere (as a problem 'other cultures' have yet to deal with). Sexism is present. That is one starting point. To answer this question 'why sexism now?' more fully I will give you the story of how this special issue came about. It began its life as a conference held at the Centre for Feminist Research at Goldsmiths in 2014. (2) It was in fact the inaugural conference for this new centre. In over 20 years as a feminist academic (including being based in Women's Studies for 10 years) this was the first academic event I had ever attended with sexism in the title, or in which sexism was identified as the key thematic. This fact, I think, should be startling, especially given, as Ulrika Dahl notes in her contribution, we might expect challenging sexism to be part of the job description for feminist academics. If anything, the word sexism seems to have 'dropped out' of feminist theoretical vocabularies. I want to offer some speculations on why this might be the case. One reason might be the strategic mobilisation of the language of feminist success: as if disciplines have been transformed by feminism such that critiquing sexism is no longer necessary; or as if we have finished that task and we have now moved on. I say 'as if' for a reason. In recent years students have relayed to me how feminism itself is often, within their disciplines, identified as passe, as old-fashioned, dated. In a curriculum review we conducted in my own college, we were struck by how many courses--including Cultural Studies--did not engage with feminist theory at all, even when feminist work had obvious relevance to the topic. We found numerous courses organised around or even as a white male genealogy. We find that: once the pressure to modify the shape of disciplines is withdrawn they 'spring back' very quickly into that old shape. Feminists have to keep pushing otherwise things quickly reverse to how they were before. The history of the 'spring back' mechanism is impossible to separate from the history of feminist exhaustion. Which is to say: the very necessity of having to push for some things to be possible can be what makes them (eventually) impossible. Something might not come about not because we have been prevented from doing something (we might even have been officially encouraged to do something) but when the effort to make that thing come about is too much to sustain. …

Numerical simulation of flexible blank drawer formation

This paper presents a finite element model for a technology of Fexible Blank Drawer Formation (FBDF) for the forming process.In order to verify the feasibility and versatility of the FBDF technology, we performed numerical simulations for multi-point saddle-shaped parts, and for convex curved surface and hemispherical parts. We analysed the effect of different forming methods on wrinkling and cracking, stress and strain distribution as well as circulating and spring back. Also, we studied the effect on the FBDF result caused by the chucking power, blank drawer force, friction coefficient and material parameters. The results showed that under the same conditions, the parts formed by FBDF technology showed uniform stress and strain distribution with little spring back. The blank drawer force can efficiently restrain the defects such as wrinkling and crack.

The Influence of Punch Angle on the Spring Back during V-Bending of Medium Carbon Steel

This study presents the influence of punch angle on the spring back behavior of the medium carbon steel under V-bending through experimental and analytical studies. Punch angle from 80o, 85o and 90o were applied to the samples, which were bent on a 90° V-shaped die for the spring back evaluation. Results from both the experimental and analytical method indicate that the spring back has similar results with the punch angle of 80o, 85o and 90o.

Steel Plastic Geogrid Performance Testing and its Application in the Reduction of Spring Back of Shotcrete

In order to solve the problems of high springback of sprayed concrete and high dust concentration in the boltnetting support of underground engineering, research the mechanical properties of steel plastic geogrid and analyze the application of steel plastic geogrid replacing the metal net in the reduction of concrete through theoretical study, laboratory test, field test and contrast analysis, thus got the conclusion that: (1) Through the analysis of influence factors of the springback of surrounding rock supporting sprayed concrete, classification is carried on with the sampling survey method. The interaction between the metal net and concrete is the main factor to influence the springback of the concrete. (2) Study the performance differences of the steel plastic geogrid and the metal net. With the advantages of tensile strength, strong durability and injection connection, steel plastic geogrid has stronger applicability, safety and stability in adjusting the stress of the surrounding rock of the roadway and coordinating its deformation. (3)Through the tensile test and the deflection test, study the relationship between the tensile strength and external load under different aperture, thus establish the relation curve between the maximum deflection and load. (4) Through the roadway engineering construction and the analysis of the data of the field test, steel plastic geogrid can greatly reduce the springback of sprayed concrete which can guide the design and construction of underground bolt-netting support engineering.

Investigation and numerical analysis of impulsive hydroforming of aluminum 6061-T6 tube

Nowadays impulsive forming processes have become popular among scientists and industrial companies due to their unique capability at increasing formability in various materials and reduction in production time and cost. In this research, finite element analysis of impulsive hydroforming on the sheet and tube was carried out using an explicit scheme and the interaction between the fluid and the shell elements representing the workpiece was approximated through the use of the surface based acoustic-structural interaction. This allowed transferring the pressure from the electrical discharge in the fluid medium, determined by the Geers and Hunter model, to the nodes representing the workpiece. The behavior of the sheet and tube was assumed to follow the Johnson–Cook structural model and the physical constants for the model were taken from other research papers. The proposed finite element model was verified by comparing the results of the model to the experiments published by another researcher and were found to be in good agreement. The FE model was applied to the impulsive forming of the tube so that the effect of discharge energy, die radius and friction coefficient could be studied in the tube electrohydraulic forming process. It is observed that the discharge energy value has major effect on the process and the friction coefficient has minor effect relative to the others. Results showed that Al6061-T6 tube did not sustain any damage even by experiencing stresses near the ultimate strength stress due to the high strain rate of the process. Elastic spring back of the tube decreased with increasing in the energy level, die radius and friction coefficient, due to the impact with the die and the lower induced stresses. Material flow into the die cavity improved by increasing in the die radius, resulting in formability improvement.

Constitutive modelling effect on the numerical prediction of springback due to a stretch-bending test applied on titanium T40 alloy

Nowadays, numerical simulation by finite element analysis is an essential tool that allows performing virtually sheet metal forming processes, and therefore to reproduce various phenomena such as springback (SB) and necking that are generated by plastic deformation. However, the quality of the model used to represent the mechanical behaviour is a determining factor for the realism of numerical simulations. To perform well, the model must reproduce all the properties of the material such as the anisotropy and the strain hardening induced by plastic deformation. The main purpose of this work is to show, by means of numerical simulations, the influence of constitutive modelling on the prediction of the degree of SB in the case of a stretch bending test. Tests have been carried out on titanium sheets which have a wide range of applications for high tech industries because of specific mechanical and physical properties. At the same time, we have investigated the dependence of some process parameters such as the clamping force on SB. In order to prove the accuracy and reliability of the proposed finite element model, experimental data were used to compare with the numerical results.

Spring back of infinite honeycomb sheets beyond plastic deformation

Cellular structures are promising for applications where high stiffness and strength are required with the minimal use of material. They are often used in applications where the plastic deformation plays an important role, such as those involving crashworthiness, energy absorption, and stents. The elastic analysis of a honeycomb sheet has been carried out in the past [1]. The present analysis extends this classical work in the elasto-plastic regime. Recoil analysis due to elastic recovery is absent from the published literature. This work aims to develop an analytical model to calculate the spring back for a simplified case, that of an infinite honeycomb sheet. An elastic-perfectly plastic material model is assumed. The recoil for a clamped beam with a load and moment applied at the free edge is analytically calculated first. This is carried out by relating the stress distribution of the cross section to the final deformed shape. The part corresponding to the elastic contribution is subsequently subtracted in order to obtain the final configuration after the external load is removed. This simple elasto-plastic analysis is then incorporated into the analysis of an infinite sheet made of uniform hexagonal cells. The translational symmetry of the lattice is exploited along with the analysis of a beam under tip loading through to plastic stage and recoil. The final shape of the struts upon the removal of the remote stress is completely determined by the plastic deformation which cannot be recovered. The expression for the beam thus obtained is then used to build an analytical model for an infinite honeycomb sheet loaded in both directions.

Warm dynamic compaction of Al6061/SiC nanocomposite powders

Powder dynamic compaction is one of the new methods for the production of nanocomposites. In this paper, Al6061/SiCnp nanocomposite is compacted using warm dynamic compaction by simultaneous application of heat and dynamic compressive waves. A comparison between the results of this study and those reported in the literature confirms that the warm dynamic compaction methods are superior to cold dynamic and quasi-static compaction method in densification of nanocomposites especially for high volume fractions of nano particles reinforcement. Mechanical and microstructural characterization of the samples is carried out to investigate the effects of temperature and content level of reinforcement. The results indicate that the increase of nano reinforcement content in warm dynamic compaction leads to reduction of the relative density and increase of hardness and the compressive strength. Moreover, higher compaction temperatures result in enhanced density and lower hardness. It is shown that samples compacted using warm dynamic compaction exhibit lower spring back and ejection force and also the distribution of mechanical properties is significantly more homogeneous. Sensitivity analysis showed that temperature increase has the most effect on homogeneity improvement and reducing dimensional change. Microscopic analyses verified that higher compaction temperature leads to lower porosity and improved metal particle bonding. It seems that agglomeration of nanoparticles and destructive phenomena such as capping and delamination are the main reasons for loss of compressive strength at room temperature. These issues are resolved in warm dynamic compaction by increasing the compaction temperature which leads to better bonding between particles.

Can a social enterprise sustain operational efficiency and profitability in an open market? The case of Spring Back Recycling

Social enterprises often seek to provide their stakeholders with economic, social, and environmental benefits. We find that developing and sustaining a social enterprise can challenge profitability in a competitive, profit-maximising marketplace. Much of the public and non-profit economic literature questions the ability of a social enterprise, with a primary emphasis on providing a social or environmental good over maximising profit, to sustain a competitive position in a commercial marketplace. For the past five years, we have conceived, developed, and implemented a social entrepreneurial venture with an aim of sustaining profitability. Spring Back Recycling is a service-oriented social enterprise that provides transitional employment, a sustainable source of revenue and earned income, and an operational enterprise that diverts millions of pounds of solid waste. Spring Back's distinctive business model and value proposition have not only achieved sustainable profitability, but have also been able to differentiate the enterprise from traditional, profit-maximising solid waste management firms.

Numerical Simulation of Middle Thick Plate in the U-Shaped Bending Spring Back and the Change of Thickness

In this paper, the typical U-shaped pieces were taken as the object of study and the finite element numerical simulation software Dynaform is applied to simulate the effect of sheet metal bending. The U-shaped bending spring back and its thickness change are analyzed. The influence law of main parameters of die structure to sheet thickness change and the spring back amount are obtained by combining with the orthogonal analysis method. Finally a set of the optimal parameter combination is found, the spring back of U-shaped piece and the change of the thickness are controlled in a reasonable range.

Numerical Simulation and Neural Network Prediction the Cold Bending Spring back for Ship Hull Plate

The accurate prediction of the spring back has great significance to the cold bending of plates. Based on the analysis of the square non pressure head CNC bending machine forming principle, the finite element model of the cold forming of the hull plate surface was established using the ANSYS/LS-DYNA finite element software. And the spring back computing research was done on the thickness of 8 mm to 16 mm. The influence rule of the thickness to spring back was analyzed. And the numerical simulation and experimental results of spring back comparison verified the reliability of finite element simulation. Then the prediction model of the plate thickness and the spring back was established using neu- ral network which is based on nonlinear dynamic system and the test sample spring back was predicted. The results of simulation show that the BP neural network can predict the spring back transformation trend very well by comparison with the results of numerical simulation and provides a reliable basis for spring back control. A new idea was proposed for the ship hull plate CNC forming by the application of neural network.

Micro scale laser shock forming of pure copper and titanium sheet with forming/blanking compound die

A new process fabricating micro parts of thin metal foils by laser shock waves with forming/blanking compound die is reported in this article, in which flexible rubber material was used as the soft punch to act on the thin metal sheet. Systematic studies were carried out experimentally on the process with different laser energies and materials. The formed parts were examined in terms of their morphology, surface roughness, forming depth and mechanical properties (including nanohardness, plasticity and elastic modulus) characterized by nanoindentation test. According to the results, the ablation states of confinement medium and the surface roughness of the different regions change with energies. Additionally, the proper energies are necessary to form complex parts and the forming process can be applied to manufacture parts with good surface quality. What׳s more, the nanoindentation test results showed that the nanohardness, plasticity and elastic modulus of material were increased after impact. The increase in nanohardness and plasticity can attribute to higher stiffness of the parts. The enhanced elastic modulus indicates an increased stiffness of the parts, providing an evidence for the reduced spring back of copper during laser shocking.

Evaluation of a 7050-TAF aluminum alloy submitted to creep age forming

CAF process combines creep and precipitation hardening which are highly dependent on time and temperature. The aging cycle relax the stresses induced during the loading phase. At the end of the process stress relaxation induces shape changes in the part but significant spring back is observed (about 70%). Usually CAF cycles for 7XXX alloys use times around 20 h and temperatures in the range of 120°C to 190°C. In the present work CAF tests were performed using the alloy 7050 in an intermediate condition named Temper to Age Forming (TAF). Using the alloy 7050-TAF resulted in significant process time reduction. From TAF temper, only 8 hours are necessary to achieve properties comparable to T74. Coupons were submitted to CAF in two levels of initial stress, 190 MPa and 290 MPa, resulting in spring back values of 70% and 60 % respectively. In addition, constant load creep tests were performed in the same stress levels and time of CAF tests to find the creep strain values. Creep tests performed under 190 MPa resulted in strain values around 0,1% after 8 h. On the other hand creep tests performed under 290 MPa failed after 7 h with creep strain values of 1,7%. Results obtained are close to that found in previous studies and it is possible to conclude that the use of alloy 7050 in TAF condition allows CAF to be done in 8 hours, since the initial stress is lower than 290 MPa.

Stamp Forming of Polypropylene Based Polymer-Metal Laminates: The Effect of Process Parameters on Spring Back

This paper investigates the effect of process parameters such as Blank Holder Force (BHF) and Feed Rate, on the spring back behavior of a polymer metal laminate (PML) system comprised of aluminum and polypropylene. Specimens were formed over a hemispherical punch in stamp forming process. A novel real time strain measuring system, ARAMIS, was employed to capture the strain evolution during forming. The results of this work indicate that both BHF and feed-rate exert influence in PML spring back behavior. Fundamental correlation between strain evolution during spring back and the shape of the finished part will be presented. A major finding from this work is that aluminum dominates the spring back behavior of PML in stamp forming.

Effect of Al<sub>2</sub>O<sub>3</sub> Content and Process Variables on Structure and Properties of Al-Al<sub>2</sub>O<sub>3</sub> Compacts

Aluminium-alumina compacts with varying wt% of alumina were compacted in the pressure range of 115 - 290 MPa. Compacts prepared at 290 MPa pressure, were sintered in an argon atmosphere at 573, 673, 773 and 873 K for 1 hour. The green density, % porosity, % spring back and hardness of the green compacts were determined. Scanning Electron Microscopy was carried out to observe the morphology of pores and alumina particles in green and sintered compacts. The present study indicates that, densification of the compact increases with increasing compacting pressure and decreases with increasing alumina content. Maximum density achieved is 93% for pure aluminium compacts and decreases to 85% for Al-20 wt% alumina compacts. Grain growth of aluminium particles is noticed in the compacts after sintering at 773 and 873 K. Dispersion of fine alumina particle in the aluminium matrix occurs predominantly in the compact when sintered at 773 K which results in increase in hardness value.

Experimental and Numerical Analysis of Negative Spring back in Interstitial Free (IF) Steel

One of the most sensitive features of sheet metal forming processes is the elastic recovery during unloading, called spring-back, which leads to some geometric changes in the product. This phenomenon will affect bend angle and bend curvature, and can be influenced by various factors. In this research, the effects of anisotropy i.e., the rolling direction of 0° , 45° 90° of ultra low carbon steel Interstitial Free (IF) Steel in V- bending with a punch corner radii of 7.5mm, were studied by experiments and numerical simulations. Comparison between the experimental and the finite element simulation results are also presented and found to be in close agreement.

Experimental determination of spring back and thinning effect of aluminum sheet metal during L-bending operation

In automotive industry, significant efforts are being put forth to replace steel sheets with aluminum sheets for various applications. Besides its higher cost, there are several technical hurdles for wide usage of aluminum sheets in forming. Major problems in aluminum sheet metal forming operations are deformation errors and spring back effect. These problems are dependent on the number of parameters such as die and tool geometry, friction condition, loading condition and anisotropic properties of the metal.To predict the exact shape, the geometry based punch contact program must be used. The shape changes once the punch is withdrawn, because of the materials elasticity. Prediction of such a spring back effect is a major challenging problem in industry involving sheet metal forming operations. It also needs applying appropriate back tension during the forming complex shapes. Slight deformation of the metal leads to non-axisymmetric loading. One can predict the residual stress by determining plastic and elastic deformation. Thus appropriate spring back effect can be investigated.The present investigation was carried out to determine the spring back and thinning effect of aluminum sheet metal during L-bending operation. Number of specimens with thickness varying from 0.5mm to 3.5mm were prepared. The experiments were conducted for different clearances between punch and die. It is observed that, beyond a particular clearance for each thickness of the sheet metal, the spring back and thinning effects were linearly increasing. However, below the critical clearance, scratches on the surface of the sheet metal were seen due to wear. The scratches were analyzed through Scanning Electron micrographs. As the clearance between punch and die reduces further, more wear on the punching surface was observed. And, as the clearance increases it leads to increase the spring back effect and fracture propagation.

An Elastic–Plastic Model for Single Shot-Peening Impacts

A model was developed for impacts of elastic perfectly plastic spherical particles with impact velocities up to 250 m/s. The model is based on the two master curves, for normalized pressure $$\bar{H}$$ and projected contact area c 2, which both are functions of the representative strain Λ at maximum impact. The model and its parameters were fitted to finite element results for elastic perfectly plastic and strain rate-independent materials. It was applied to a wide range of materials with different ratio between yield stress and elastic properties, different ball sizes and impact velocities. The impact model predicted the results from finite element method for contact radius, maximum impact depth in both target and ball as well as remaining impact depth in target and ball. The remaining impact depth was determined from elastic spring back with Hertzian and quadratic pressure at maximum impact. The rebound velocity was also estimated by following the load-deformation path during spring back. If the strain rate-compensated yield stress was used for the master curve parameters, then the model predicted the impact results also for the investigated strain rate-dependent materials.

Improvement of a high velocity compaction technique for iron powder

Water atomized pure iron powder was compacted by high velocity compaction (HVC) with and without upper relaxation assist (URA) device. The influence of URA device on green density, spring back, green strength and hardness was studied. Morphological characteristics of the samples were observed by scanning electron microscope (SEM). Green strength of the samples was measured by computer controlled universal testing machine. The results show that as stroke length increases, the green density, green strength and hardness of the compacts increase gradually. At the identical stroke length, the green density of the compacts pressed with URA devise was 2% higher than the compacts pressed without URA device. The green strength and hardness of the compacts pressed with URA device were higher than the compacts pressed without URA device. Furthermore, the radial spring back of the compacts decreased gradually with the increment in stroke length, whilst that of compacts prepared with URA device was lower.

Improvement on CAE Model Considering Surface Deformation of Tools in Contact with Blank Sheet for Accurate Torsional Springback Prediction in High Strength Steel Part Forming

It is difficult to predict springback, particularly in torsion, with high accuracy by FE simulation. Generally, more accurate springback prediction havs been achieved mainly by the improvement of material modeling such as Baushinger effect and plastic anisotropy models. It is also proved that tool deformations can greatly influence on the accuracy of torsion springback prediction as shown in the authors’ study [Esaform 2012]. The study shows that FE simulation using elastic tool model has 30% more accuracy in predicting torsional spring back in a curved hat shape than that by rigid tool model. But full elastic tool modeling is tedious work and FE calculation with the elastic tool model needs enormous time.There are two kinds of tool deformation during a press forming: tool deflection as a whole, and surface deformation where the tool is in contact with the steel sheet. Three forming experiments were carried out with an insert block of different stiffness, which touch steel sheets directly, in this study. The results revealed that surface deformation of a tool has great influence on torsion springback of a curved hat shape. Based on the results, a new tool modeling is proposed in this study. In the model, the part of a tool in direct contact with a blank sheet is elastic and the other part is rigid. That means the model deals with only surface deformations of tools in FE simulation. By the new model, the accuracy of torsion springback prediction of a curved hat shape was improved with less calculation time.