Case Study of Strength Calculation and the Possible Repair Options for Screw Thread Damages

Thread Strength and repair capability are critical to successful screw joints for any mechanical assembly. This paper explores the effect of the thread damage utilizing hand calculations, the margin of safety (MOS) for internal & external threads and compares with the required design criteria limit. Hence, the reduction in thread capability is analyzed in terms of shear and bearing strength of threads. This paper also emphasizes the Industry-standard repair techniques such as Helical inserts, Oversize inserts, and Twinserts with limitations and expected process/techniques. Advanced thread repairs in the market such as solid-body thread inserts (key-style, Time-sert, Big-sert) are also discussed Keywords: Thread damages, Shear strength, bearing strength. STI (Screw thread insert)

Test of Designing and Manufacturing a Polyether Ether Ketone Endoprosthesis for Canine Extremities by 3D Printing

Total limb amputation is quite common in small animals, although most of the indicated pathologies do not need such a restrictive procedure. Exo-endoprosthesis is a suggested alternative for the enhancement of the biomechanical situation of these patients. 3D printing of the internal part of exo-endoprostheses in polyether ether ketone (PEEK) is evaluated. Two different shapes of this internal part—one for radius’ and the other for cylindrical medullary cavities—were assessed. Proper PEEK temperature settings for 3D printing, the internal part of exo-endoprostheses, by fused filament fabrication (FFF) were obtained. Printing trials were carried out for different dimensions and printing orientation of these parts to achieve the best bone anchorage and thread strength outcomes. Pull-off strength tests for different surfaces of the internal part were performed with a best outcome for positive surfaces. All printed internal parts were inserted in canine tibiae and radii for an ex vivo assessment of bone anchorage and thread strength parameters. The best printing results were obtained at 410 and 130°C of the nozzle and bed temperatures, respectively. Also, a positive correlation was observed between the printing code, quality, and take-off time, while inverse correlation was shown between the take-off and the printing code, or quality, just like the print-bed temperature and the printing code. The positive surfaces had the best pull-off strength outcomes. Excellent bone anchorage and thread strength outcomes were obtained for one variant of each internal part shape. Designed devices had shown good threaded rod’s fitting inside the PEEK plug and perfect bone anchorage of the PEEK plug for tibiae and radii. In addition, iteration of manufacturing PEEK small devices by FFF technology has been shown due to small standard deviation of most variants.

Investigating the Performance of Sewn Seams from Woven Fabrics

Seam performance ensures the durability, attractiveness, strength etc. of the sewn garments. Fabric types, fabric densities, fabric strength, seam types, sewing thread count, thread strength, stitch densities and stitch types influence the performance of a sewn seam. This paper investigates the performance of sewn seam of various structure of woven fabric. The variables of this research are stitch densities (SPI), sewing thread count, seam types and woven structures. We conduct our research over plain, twill 2/1, twill 2/2, oxford and poplin woven structure. Firstly, we apply lockstitch (301) to produce superimposed, lapped and bound seam on the woven sample by using thread count 27 Tex, 30 Tex, 20/2 Tex, 40 Tex, 40/2 Tex, 40/3 Tex having stitch densities (SPI) 8, 10 and 12. Then according to ASTM D1683 standard, we measured the tensile strength test and recorded the seam breaking strength (N). We apply error bars over each diagram to investigate the standard deviation. Finally, we discuss four hypothesis to conclude our research work. We found higher seam breaking strength with the increase of thread count and SPI. The bound seam samples has shown superior seam breaking strength than superimposed and lapped seam; poplin structure surpassed to others. The seam efficiency of the samples varies from 60–90% and do not exceeds 100%. Finally, we found some significant alternatives hypothesis of the population since F values exceeded F critical values for the sewn seam.

Only as strong as the weakest link: structural analysis of the combined effects of elevated temperature and pCO2 on mussel attachment

Predicting how combinations of stressors will affect failure risk is a key challenge for the field of ecomechanics and, more generally, ecophysiology. Environmental conditions often influence the manufacture and durability of biomaterials, inducing structural failure that potentially compromises organismal reproduction, growth, and survival. Species known for tight linkages between structural integrity and survival include bivalve mussels, which produce numerous byssal threads to attach to hard substrate. Among the current environmental threats to marine organisms are ocean warming and acidification. Elevated pCO2 exposure is known to weaken byssal threads by compromising the strength of the adhesive plaque. This study uses structural analysis to evaluate how an additional stressor, elevated temperature, influences byssal thread quality and production. Mussels (Mytilus trossulus) were placed in controlled temperature and pCO2 treatments, and then, newly produced threads were counted and pulled to failure to determine byssus strength. The effects of elevated temperature on mussel attachment were dramatic; mussels produced 60% weaker and 65% fewer threads at 25°C in comparison to 10°C. These effects combine to weaken overall attachment by 64–88% at 25°C. The magnitude of the effect of pCO2 on thread strength was substantially lower than that of temperature and, contrary to our expectations, positive at high pCO2 exposure. Failure mode analysis localized the effect of temperature to the proximal region of the thread, whereas pCO2 affected only the adhesive plaques. The two stressors therefore act independently, and because their respective target regions are interconnected (resisting tension in series), their combined effects on thread strength are exactly equal to the effect of the strongest stressor. Altogether, these results show that mussels, and the coastal communities they support, may be more vulnerable to the negative effects of ocean warming than ocean acidification.

The role of capture spiral silk properties in the diversification of orb webs

Among a myriad of spider web geometries, the orb web presents a fascinating, exquisite example in architecture and evolution. Orb webs can be divided into two categories according to the capture silk used in construction: cribellate orb webs (composed of pseudoflagelliform silk) coated with dry cribellate threads and ecribellate orb webs (composed of flagelliform silk fibres) coated by adhesive glue droplets. Cribellate capture silk is generally stronger but less-extensible than viscid capture silk, and a body of phylogenic evidence suggests that cribellate capture silk is more closely related to the ancestral form of capture spiral silk. Here, we use a coarse-grained web model to investigate how the mechanical properties of spiral capture silk affect the behaviour of the whole web, illustrating that more elastic capture spiral silk yields a decrease in web system energy absorption, suggesting that the function of the capture spiral shifted from prey capture to other structural roles. Additionally, we observe that in webs with more extensible capture silk, the effect of thread strength on web performance is reduced, indicating that thread elasticity is a dominant driving factor in web diversification.

An Approach to Seam Strength Prediction Using Residual Thread Strength

Owing to a high amount of stress, seam failure in workwear fabrics makes the fabric unsuitable although the fabric strength is high. It is therefore important to predict the seam strength to ascertain the performance of the garments during use and determine the required thread strength and stitch density to match the required seam strength. In all of the earlier predictive equations, seam strength is predicted from thread strength and stitch density along with some multiplicative factors. During the sewing process, a substantial loss in needle thread strength occurs; therefore, the thread becomes weaker than expected after incorporation into the seam. In this paper, the effects of various machine and process parameters are studied on thread strength loss and seam strength. The seam strength is predicted from the loop strength after considering the loss in thread strength. It is observed that higher seam strengths are observed when stronger threads are used for sewing. Loss in thread strength has a significant influence on the seam strength. Seam strength can be predicted using stitch density and thread loop strength, by considering the loss in thread strength during the sewing process. A closer match between predicted and experimental seam strength is possible.

Effect of Workwear Fabric Characteristics on the Changes in Tensile Properties of Sewing Threads after Sewing

During sewing at high speed, the needle thread is subjected to repeated tensile stresses, heat, bending, pressure, torsion and wearing. These stresses act on the thread repeatedly and the thread passes 50–80 times through the fabric, the needle eye and the bobbin case mechanism, before getting incorporated into the seam. As a result both the sewing thread and the yarns in the fabric get abraded/ severed during the seaming process. A number of researchers observed that there could be 30% to 40% strength loss in the cotton needle thread after sewing. The extent of damage becomes more critical if the fabric being used is of a dense, thick and heavy construction. A number of studies have been carried out on thread strength loss after sewing, but the impact of fabric characteristics on thread strength loss is still unexplored. In this paper, the effect of weight and fabric composition of workwear fabrics, on the changes in the tenacity, breaking elongation and initial modulus of the needle thread has been studied. The tenacity and breaking elongation loss increase with increase in fabric weight for staple threads and remain unchanged for core spun threads. The loss in initial modulus increases for polyester threads as fabric weight increases, and decreases for cotton thread. When sewn on polyester-cotton fabric of same weight, the cotton thread shows decrease in tenacity and breaking elongation loss, whereas loss in initial modulus increases. The polyester core spun threads show exactly opposite change, i.e. tenacity and elongation loss increase and loss in initial modulus decreases when sewn on polyester-cotton fabric.