Mechanical Properties of Aluminium Bracket Strengthening

The aim of the research is laboratory investigation of aluminium brackets employed to fasten lightweight curtain walls to building facilities. Tensile loads perpendicular to end plates (vertical) were applied here. The author focused on the solutions intended to increase the load-carrying capacity of aluminium brackets applying the plain washer form A (DIN 125; ISO 7089), plain washer with an outer diameter about 3d (DIN 9021; ISO 7093) and additional cover plates (straps) in the location of bolt anchoring on the base plate. The aluminium brackets were tested on a steel base and concrete substrate. The flexibility of anchoring strongly affects the increase of the end plate middle point displacement and movable crosshead displacement.

Degradation of Functional Properties of Pseudoelastic NiTi Alloy Under Cyclic Loading: An Experimental Study

The influence of the cyclic loading on the functional properties of NiTi was studied. Cylindrical specimens with a diameter of 4 mm and a gage length of 12.5 mm were tested under uniaxial cyclic loading with control crosshead displacement at a temperature of 0°C. The dependences of the stress and strain range as well as dissipation energy on the number of loading cycles at different initial stress range were analysed. During the first 10 loading cycles, a rapid decrease in the strain range and energy dissipation was observed. Dissipation energy was invariant to the loading cycles’ number at N > 20 cycles and to the stress range that did not exceed the martensite finish stress level, was within the same scatter band and can be described by the single dependence. With the stress range growth at N < 20 cycles from 509 to 740 MPa, the value of dissipation energy increases and that of relative dissipation energy decreases. Loss coefficient, which characterises material damping ability, significantly decreases during the first 10 loading cycles and remains practically unchanged up to the failure of the specimens. At the stabilisation area, the loss coefficient is almost non-sensitive towards the stress range.

Standard and non-standard deformation behaviour of European beech and Norway spruce during compression

The goal of the study is to investigate the non-standard deformation behaviour of wood loaded by compression parallel to the grain. This is represented as a negative increment of strain in the range of plastic deformations when the load continues to increase. The objectives of this study are to point out this problem and to provide its description based on the deformation fields that have been analysed using three approaches: a) full-field optical technique based on digital image correlation (DIC); b) “clip on” extensometer and its virtual analogy, and c) crosshead displacement method. Further, the negative strain phenomenon was studied depending on the sample length. The samples were made from the European beech (Fagus sylvatica L.) and Norway spruce (Picea abies L. Karst.). Based on the strain analysis, it can be concluded that the deformation field consists of three sub-regions exhibiting different stiffness values (three-spring model). The failure of less stiff zones near the compression plates during the “non-standard” compression behaviour causes almost zero compression deformation of the stiffer middle zone or even leads to its expansion. The three-zone heterogeneity of deformation field induces a deviation of the displacement and strain measured by the proposed approaches. This phenomenon substantially influences the resulting longitudinal Young’s modulus and, therefore, should be of concern when measuring wood in such mode.

The Use of Crosshead Displacement in Determining Fracture Parameters

In determining the fracture toughness of a test specimen, standards currently require either locally-measured load-line displacements or clip gage displacements. In order to measure these parameters, secondary sensors generally need to be installed and calibrated, which often comes at a higher cost. As crosshead displacements are automatically measured in most modern material test machines, use of the crosshead measurements alone would be less expensive. Although much criticism exists on the accuracy of this approach in determining CTOD values, the method can still prove sufficiently accurate for many applications. The current paper aims to assess the magnitude of the errors that arise from using the crosshead displacement in fracture mechanics testing of steels with the Single Edge Notched Bending (SENB) specimen geometry. The results show that for steels with sufficiently large toughness, the use of the crosshead displacement to calculate J and convert to CTOD produces results within 10% of calculating the CTOD directly with conventional techniques.

An Investigation into Strain Partitioning in Mismatched HSLA-65 Steel Welds

The aim of this study was to quantify strain partitioning in HSLA-65 joints, welded with three types of weld filler: 6011 undermatched weld filler, 7018 matched weld filler, and 9016 overmatched weld filler. Strain measurements were made using a three-dimensional digital image correlation system while specimens were tested on a displacement controlled servo-hydraulic test frame. Crosshead displacement rates ranged from 0.056 mm/s to almost 56 mm/s. Coupons were cut from flux-core arc welded HSLA-65 plates to characterize the base metal, weld filler materials, and mismatched welds. Constitutive material properties could be extracted reliably for all coupons at the lowest displacement rate and showed that, as expected, all weld fillers had similar elastic modulus values but different yield strengths. A comparison of the peak strains at 85 per cent of maximum elongation showed that overall the failure strain was inversely related to the crosshead displacement rate. Analysis of the mismatched coupons found that the failure location was a function of weld filler and was independent of strain rate. Higher magnification imaging of the weld nugget showed that strain partitioning occurred within the weld zone, with slightly lower strains in the cap pass as opposed to the root pass.

Mechanical Properties of Feedstock Material for Fused Deposition of Ceramics

A scientific methodology to characterize the critical mechanical properties of feedstock material for fused deposition of ceramics has been developed. A detailed discussion of the methodology of mechanical characterization and results for lead zirconate titanate (PZT) fused deposition of ceramics (FDC) feedstock is presented. The effect of storage time, temperature and crosshead displacement rates on the mechanical properties of the PZT FDC feedstock was studied. The modulus and the failure stress increase with displacement rate. The modulus and failure stress decrease with temperature indicating the necessity for cooling filaments prior to entrance to liquefier. The modulus also decreases with storage time in 50% RH while failure strain increases with storage time in 50% RH.

Temperature-Dependent Onset of Yielding in Dislocation-Free Silicon: Evidence of a Brittle-To-Ductile Transition

An investigation of the brittle-to-ductile transition (BDT) in silicon has been conducted on essentially dislocation-free silicon test specimens made by photolithography. No pre-cracks or additional dislocation sources were introduced into the samples. Three-point bending tests of the samples reveals a well defined transition from brittle fracture of the specimens to complete yielding near 732°C at a crosshead displacement rate of 0.1 mm/min. Limited plasticity is observed below 732°C but is insufficient to prevent crack propagation suggesting that yielding is not dislocation mobility limited. Instead the transition may be controlled by the nucleation of a sufficient density of dislocations. Further support comes from the results of experiments conducted at temperatures below 732°C in which samples were rapidly pre-loaded within the linearly elastic regime, then immediately retested. This rapid pre-loading results in a lower transition temperature. This would not be expected if dislocation mobility controlled the BDT. Instead, it is believed that the transition only occurs when a sufficient density of dislocations has nucleated within the sample. In these experiments, the pre-loading event may increase the dislocation nucleation rate. The source of the dislocations in these defect free samples is still under investigation.