Spring Steel Strip Research Articles

Microstructure and Mechanical Properties of an Austenitic CrMnNiMoN Spring Steel Strip with a Reduced Ni Content

The article presents the mechanical properties of the austenitic stainless steel X5CrMnNiMoN16-4-4 after deformation by cold rolling and subsequent short-term tempering (deformation and partitioning (D&P) treatment). Tensile strengths of 1700–900 MPa and beyond were achieved both after work hardening and in the D&P-treated strip. The initial state of austenite in terms of grain size and pre-strengthening, as well as the selected cold rolling temperature significantly influenced the deformation-induced formation of α’ martensite and thus the flow and hardening behavior of the steel. The usage of two different rolling temperature regimes showed that the strength properties in the cold strip can be specifically adjusted. Lower deformation-induced martensite fractions enabled a larger thickness reduction of the strip without increasing the rolling force, while high deformation-induced martensite fractions led to strong hardening at low deformation levels. The D&P-treatment permits the strength of the cold-rolled strip with a predominantly austenitic microstructure to be increased to the required level. The total elongation of such a D&P strip was well over 2%. The D&P treatment of the spring steel strip is a cost-effective alternative to conventional tempering treatment.

Folding the Carpenter’s Tape: Boundary Layer Effects

Abstract The “carpenter’s measuring tape” is a thin spring-steel strip, preformed to a curved cross section of radius R, which is straight when being used for measuring. Under bending moments, it forms a localized hinge, in which the transverse curvature is suppressed, and the longitudinal radius r is approximately equal to R. Rimrott made a simple strain energy analysis of the hinge region for isotropic material, which predicted that r = R. Both experimental observations and finite element computations show that ξ = r/R > 1, where the value of ξ exceeds unity by up to 15%, depending on whether the tape is bent in “equal-sense” or “opposite-sense” curvature; ξ varies linearly with Poisson’s ratio in both cases. We make a minor change to Rimrott’s analysis by introducing a boundary layer, in order better to satisfy the physical conditions at the free edges; this successfully accounts for the observed behavior of the tape.

Development of a Stainless Austenitic Nitrogen-Alloyed CrMnNiMo Spring Steel

The generation of a nickel-reduced, stainless spring steel strip with a thickness of 0.2 mm, producible under industrial conditions, is the aim of a transfer project together with the Institute of Metal Forming/TU BAF and the Auerhammer Metallwerk GmbH within the DFG Collaborative Research Centre (CRC) 799. The spring steel strip should exhibit a tensile strength of ≥1700 MPa in work-hardened and partitioned state. The mechanical and corrosive properties of the steel strip should be equal or better than those given for 1.4310 steel (AISI 301). The article presents the results of laboratory alloys focused on the design of steel strips, which meet the requirements for a cost-effective production. The results presented relate to steel design, microstructure formation, temperature-dependent mechanical properties, and corrosion resistance. Four alloys of the type X5CrMnNiMoN16-x-4 with manganese contents of approximately 2 to 6 wt.-percent were investigated. The austenitic steel X5CrMnNiMoN16-4-4 with TRIP/TWIP effect was selected for deformation and partitioning treatments. Its deformation-induced α’-martensite formation significantly contributes to the work hardening of the steel. A short-time annealing treatment (partitioning) further increases the strength properties.

A Lightweight Linear Actuating System for Finger Articulation: A Proof-of-Concept Study.

This paper provides a proof of concept for an actuating system comprised of a linear actuator and a spring steel strip that enables bidirectional articulation of a finger by transmitting the force directly to the finger tip. This proposed design can be distinguished from other orthosis designs, which use rigid linkages or cables with DC motors or fluidic systems for force generation and transmission. We designed an experimental setup with a 3D-printed model finger to mimic a passive human finger on which the actuation system was mounted and tested. The finger was positioned such that it would curl upward to lift various masses when articulated by the actuating system to demonstrate the system's force generation capability. We tested two linear actuators and two steel strips, using a wide range of masses to determine which would be the most suitable components for our design. We analyzed motion profiles, joint angles, force generation, and actuator stroke velocities during various experimental trials. Our results demonstrate that our actuating system is capable of generating sufficient forces and motions with an adequate response time to be used in the design of a hand orthosis for grasping/releasing assistance. From our tests, a prototype was designed with three linear actuators positioned on the dorsal side of the hand and actuated the thumb, index, and middle fingers. Future work will include sensor integration and performance evaluation of the orthosis.

Determination of Tensile and Compressive Moduli of Polymer Composites Using Three Points Cantilever

In this work a technique is proposed to use bending test in order to determine the tensile and the compressive moduli of plastic sheets as well as polymer composites. A two- component free ends beam deflected in a three point cantilever is used to determine tensile and compressive moduli. Using small deflection equations and the theory of two- component beam, tensile and compressive moduli are then determined via computer program. The beam is composed of two components; spring steel and polymeric strip of the same width. These two components are bonded together with special glue. Two different types of material sheets were tested. The results show that both materials have different tensile and compressive modulus. To verify the model, uniaxial tensile tests were also performed. Taking the values of uniaxial tensile tests as reference showed acceptable accuracy at the proposed method.

In Situ Eddy-Current Testing on Low-Pressure Turbine Blades of Aircraft Engine

Abstract To realize in situ testing on low-pressure turbine blades of aircraft engines, eddy-current testing was studied through probe design, artificial defect sample testing, and practical field applications. The eddy-current probe was composed of a differential coil with dual magnetic cores, flexible spring steel strip, and elongating composite shank, which, respectively, provided high detection sensitivity on the turbine blade defect, appropriate contact between the probe and the curving blade surface, and adequate extent for the long distance of in situ inspection. Practical applications in engine turbine blades testing proved that the eddy-current probe successfully solved the in situ testing difficulties, including poor accessibility, limited detection space, and strong interference signals.

Prediction of Springback in Metal Forming of Diaphragm of Automotive Horn Based on BPANN

The spring steel strip 50CrVA which is cold rolled was applied to manufacture the diaphragm of the automotive horn by means of sheet metal forming. The combination of the experiments with back-propagation artificial neural network (BPANN) is used to solve the springback problem of the diaphragm. Experiments have shown that a 4-8-1 BPANN is able to predict the springback of the diaphragm successfully, and the network is able to model the relationship between the springback of the diaphragm and the process parameters rationally. BPANN simulation results and experimental ones have shown that the springback of the diaphragm is particularly influenced by such parameters as blank thickness, Young’s modulus, punch radius and yield ratio. Furthermore, the springback of the diaphragm decreases with the increase of blank thickness and Young’s modulus, but increases with the increase of punch radius and yield ratio.

Analysis of Fracture Failure of Diaphragm of Non-Contact Electronic Horn

The fracture of the diaphragm is the main failure pattern of the non-contact electronic horn. The spring steel strip 50CrVA which is cold rolled was applied to manufacture the diaphragm of the non-contact electronic horn by means of sheet metal forming. The combination of the experiments with finite element method (FEM) was used to reveal mechanism of fracture failure of the diaphragm. The displacement field, the effective strain field and the effective stress field at the maximum amplitude value are obtained by simulating the genuine vibrating state of the diaphragm with the help of ANSYS finite element code. The maximum stress zone of the stress field of the diaphragm is responsible for the fracture zone of the diaphragm. The fatigue test of the diaphragm and microscopy of the fractured diaphragm indicates that the fracture pattern of the diaphragm agree well with finite element simulation results. Eventually, the measures to prevent the fracture of the diaphragm were taken in order to increase the endurance of the diaphragm.

Prediction of mechanical properties of 50CrVA tempered steel strip for horn diaphragm based on BPANN

50CrVA cold-rolled spring steel strip was used to fabricate the diaphragm of the automotive horn. The material parameters which were taken into account in the design of the diaphragm involve elongation, elastic limit, Young’s modulus, yield strength and tensile strength. The tempering process was carried out in order to enable the diaphragm to possess the excellent mechanical properties, such as high elastic limit, high fatigue strength and perfect stress relaxation resistance. As a nonlinear information processing system, the backpropagation artificial neural network (BPANN) was applied to predict and simulate the relationship between the mechanical properties of the diaphragm and the tempering process parameters. Experimental results show that a BPANN with 3-8-5 architecture is capable of predicting the relationship between the mechanical properties of the diaphragm and the tempering temperature successfully and lays the profound foundations for optimizing the design of the diaphragm. BPANN simulation results show that the tempering temperature ranging from 380 to 420 °C contributes to enhancing the comprehensive mechanical properties of the diaphragm including high Young’s modulus, high elastic limit and high fatigue strength.

A nonleak trough for monolayers at the air/water interface

The problem of barrier leakage in surface pressure-surface area measurements has been overcome with a trough wherein the sample is compressed inside a band of teflon-covered spring steel strip. A computer-controlled stepping motor drive applies force to one side of the band, deforming it from a rounded triangle to a ‘‘v’’ shape. The compression range extends up to 4:1 and is repeatable to ±2%. Calibration is conveniently and accurately done with a computer-interfaced video imaging and analysis system. The design greatly simplifies the construction of surface troughs and completely obviates the possibility of leakage at high surface pressures. The trough is useful for investigations involving high surface pressures and/or requiring long times.

The Shapes of Peeling Solid Films

Abstract A theory is developed to describe the shape of a long thin elastic film peeling from a rigid substrate under a constant load. The theory is verified by static measurements of spring steel strip and by slow peeling experiments using rubber and paint films. Extension of the theory to the case of viscoelastic peeling films demonstrates how the film shape in such a system depends on peeling velocity. Reasonable agreement with experiment is obtained.

On a Coupled Vibration of Propeller Blades and Shaft : 2nd Report Experiment on Free Vibration

The experimental proof of the authors' theory on a coupled vibration of propeller blades and shaft was carried out. The model was made of spring steel strip for the blades, and of ebonite bar for the shaft. The resonance-method was adopted for determining the natural frequencies of the system. The blades, put in a coil and magnetic field, were driven by alternating current generated by R-C oscillator. The maximum amplitude at the resonance was detected by a microscope. The results were in good accordance with the theory.