Ağır ticari araçlar için hızlandırılmış dinamik yorulma analiz yöntemi geliştirilmesi
Accelerated dynamic analysis method development for heavy duty vehicle
Yazar: ÜMİT BAĞDAT
Danışman: PROF. DR. HALUK EROL
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Makine Mühendisliği Ana Bilim Dalı / Makine Dinamiği, Titreşimi ve Akustiği Bilim Dalı
Derece: Yüksek Lisans, 2019
Konu: Makine Mühendisliği = Mechanical Engineering
Dizin: Bilgisayar destekli analiz = Computer aided analysis ; Mekanik titreşim = Mechanical vibration ; Titreşim frekansı = Vibrational frequency ; Yapısal hasar = Structural damage ; Yorulma dayanımı = Fatigue strength

Özet:
Otomotiv sektöründe ürün geliştirme süreçlerindeki önemli parametrelerden bir tanesi dayanımdır. Sektörde yaşanan rekabetten dolayı ürün geliştirme süreçlerinde yaşanan zaman ve maliyet baskısı, ürünlerin son kullanıcıya tam anlamıyla doğrulanmadan ulaşmasına sebebiyet verebilmektedir. Müşteri için üründeki en önemli beklentilerden biri de dayanım olduğundan dolayı, kullanım sırasında çok erken hasarlanabilen otomotiv komponentleri memnuniyetsizlik ve şikayet yaratabilmektedir. Özellikle de ağır ticari araç segmentinde kullanıcı tarafından en dikkat edilen özellik ürünün dayanıklı olmasıdır. Ürün geliştirme süreçlerinde ağır ticari araçlara ait dayanım verifikasyonu seri üretimden önce test pistleri ve laboratuvar yol simülasyon testleri ile sağlanmaktadır. Zaman ve maliyet baskısının getirdiği zorluklar altında test pistlerinde yapılan full araç dayanım testleri araç üzerindeki bütün komponentleri gerçek koşullarda müşterinin yorduğu kadar yoramamaktadır. Verifikasyonu ürün geliştirme süreçlerindeki testlerde eksik yapılan araç üzerindeki her komponent, gerçek çalışma koşullarında hasarlanma riski taşımaktadır. Ağır ticari araç segmentinde pistlerde yapılan dayanım testlerinde özellikle statik yüke maruz kalan şasi, diferansiyel, aks gibi komponentlerin müşteri korelasyonu yüksek iken şasi üzerinde asılı bulunan ve titreşim kaynaklı yorulmaya maruz kalan yakıt tankı, akü sehpası, hava tüpü gibi komponent ve alt sistemlerin müşteri korelasyonu düşüktür.
Bu çalışma kapsamında, ağır ticari araç segmentinde titreşime maruz kalan komponent ve alt sistemleri için zaman ve maliyet baskısı altındaki ürün geliştirme süreçlerinde kullanılmak üzere hızlı ve güvenilir bir test profili üretme ve analiz yöntemi geliştirilmiştir. Hedef pazar seçilen Türkiye'de ağır ticari araç segmentinde yer alan inşaat serisi kamyonlara ait komponetler müşteri şartlarında kısa sürede hasarlanabilmektedir. Çalışmanın ilk aşamasında Türkiye pazarında inşaat serisi kamyonların yoğun olarak kullanıldığı bölgelerde bulunan müşteriler ile anket çalışması yapılıp daha sonra anket sonuçlarına göre belirlenen müşterilerden şasiye asılı parçalara gelen ivme yüklerini ölçmek için yol verisi toplanmıştır. Toplanan ivmeölçer verileri, şok cevabı spektrumu ve yorulma hasarı spektrumuna indirgenerek müşteri çalışma ömrünü temsil eden, güvenilirliği yüksek hızlandırılmış test profili x, y ve z eksenleri için türetilmiştir. Laboratuvar yol simülasyon testlerinde de kullanılabilecek şekilde türetilen  profiller kullanılarak bir inşaat serisi kamyonunun akü sehpasının yorulma hasarını hesaplayabilmek için  sonlu elemanlar analizi gerçekleştirilmiştir. Sonlu elemanlar analizinin ilk aşamasında akü sehpasının doğal frekansları hesaplanmış sonraki adımda da frekans cevabı analizleri gerçekleştirilmiştir. Bu analiz sonuçları hızlandırılmış test profilleri de  kullanılarak akü sehpasının yorulma analizleri ile süreç tamamlanmıştır. Biri hafif diğeri ağır olan iki akü sehpası modeli oluşturularak gerçekleştirilen sonlu elemanlar analiz aşamasında parametrik çalışma yapılmıştır. Bu sayede geliştirilen yöntem ile tasarımların hasarlanma potansiyellerinin hızlı ve düşük maliyetle değerlendirilerek,  validasyonu daha güvenilir olan optimum ağırlıkta ürünlerin üretilebilme imkanı kazanılmıştır.

Abstract:
Day by day, competition in the automotive industry is increasing. This creates time and cost pressure on product development processes. Cost and time pressure in the product development duration blocks to produce compenents with perfect durability validation. For this reason, customers generally use the automotives with a failure potential. Early failures at the components can create dissatisfaction and complaint on customers. Especially, heavy duty vehicle customers are very sensitive in terms of durability. For this reason, durability is one of the most important parameter for the engineers during product development steps in automotive industry. Product development engineers research different alternative and practical methods for the validation processes in design phase to overcome the cost and time pressure due to competition in the automotive industry.
During product development process in terms of durability for heavy duty vehicles consists of three main steps. Developped virtual model of the vehicle is analysis with the finite element model by using some teoritical forces. After the virtual durability validation, all prototype components are manufactured and a test vehicle is assembled. Before the mass production, validation is completed with the test vehicle durability tests in the proving ground. Sometimes, durability test in proving ground can create damage some vehicle components. For this components, design are reviewed and developped. Durability tests in the proving ground are not suitable for one component validation in terms of cost and time. So, the reviewed new components are verified by the laboratory simulation tests. Input test spectrum for these tests are synthesized with the collected data from proving grounds.
For the best validation in the proving ground, full vehicle durability test prosedure is provided by customer correlation methodologies. But full vehicle durability tests in the proving ground can not create equal damage like customer conditions for whole components on the vehicle. Because a vehicle consists of approximately three thousand parts. So, customer correlation is not possible for all vehicle parts. That's why, some components have a failure risk in the customer conditions. Chassis, differantial and axle components have perfect customer correlation in proving ground durability tests. On the other hand, chassis hanging out components such as battery tray, fuel tank, air tubes have low correlation in durability proving ground tests. These components are affected by vibrational fatigue during mission life.
In this thesis, for chassis hanging out components affected by vibrational fatigue in heavy duty vehicle segment, accelerated test profile is synthesised and fatigue analysis method is improved to use during product development steps which are under the cost and time pressure. Construction tipper trucks which is a heavy duty vehicle subsegment, have so hard customer condition in Turkey market. Due to heavy conditions, in early stages especially vibrational fatigue failure occurs on the most chassis hanging out parts.
In the first step of thesis, construction sites of Turkey are investigated. According to the researches, intensive construction sites are stone pites, coal mining sites, boron mining sites, chrome mining sites magnesite mining sites, cement plants, ceramic mining sites, building construction sites, bridge construction sites, irrigation canal construction sites and dam construction site. 15 different customers which are cover these construction sites are determined to perform an survey. Contsruction customer tipper truck customers are visited in Turkey market and different survey questions asked to characterize usage conditions of the customers. With the survey work, expectation life from tipper trucks, one tour mileage, loading quantity, total mileage for one year are learned from answers. Then, all survey data are evaluated and seven customers are determined for data collection. Survey provides to select best suitable customers which are represent Turkey construction tipper truck users.
In the second step, before the road load data collection, a reference 6x4 tipper truck is selected and its chassis is instrumented with the five accelerometers to collect input load for chassis hanging out parts. After creating measurement chain with sensors, cables, data logger and software, road load data is collected for chassis hanging out parts in selected seven customer sites. Data collection scenarios for seven customers are similar with real conditions of users like load quantity, vehicle speed, driver character. For each customer, three times load scenario data are collected, three times unload scenario data collected.
In the third step, after road load data collection, zero mean process is applied for each data set. According to the expectation life of customers, a data set which represents whole working life of a tipper truck is created for each customers. After that, for each accelerometer location and each direction, shock response spectrum and fatigue damage spectrum are synthesized from this data sets. All fatigue damage spectrums which represent each sensor locations are envelopped to create one fatigue damage spectrum for all components. The same calculation method is applied for the shock response spectrum. After these process, for the three axis, three fatigue damage spectrum and three shock response spectrum are calculated to characterize all input loads for chassis hanging out components. To create fatigue daamge spectrum and shock response spectrum for tipper trucks in Turkey user conditions, fatigue damage spectrum and shock response spectrum of seven customers are envelopped. At the end of this process, for each direction, one fatigue damage spectrum and one shock response spectrum are obtained to charactireze all input loads coming from Turkey tipper truck user conditions for all chassis hanging out components. By using these shock response spectrum and fatigue damage spectrum an accelerated test profile is synthesized for each direction.
In the last step, a vibration fatigue analysis method is shown by using this accelerated test profile. For the battery tray system which belongs to tipper truck, two finite element models are created. First battery tray finite element model is same with on the tipper truck. Second finite element model is created by decreasing panels weight. Modal analysis is performed to find mode shape and natural frequencies for both model. After that, for each direction, frequency response analysis are performed with the unit acceleration input by using modal anaysis results. The aim of frequency response analysis is to calculate stress spectrum for each element in the model. Last, each stress spectrum of element is multiplied with accelerated test profiles and obtained one life stress spectrum. With this spectrum, fatigue analysis are performed to obtain one life damage for each elements at one direction by using Wöhler material curve. These analysis are performed for each direction respectively and one life damage of an element is calculated by summing x, y and z direction damages. Performed all analysis are applied for heavy battery tray model and light battery tray model. Damage result of each model are compared at the end of the fatigue calculation process.
At the end of this thesis, a fast and realiable test profile is created for tipper truck chassis hanging out parts tests and analysis. This test profile prevents full vehicle durability tests only for one component. This means that, sythesized test profile provides cost and time saving. Also, developped fatigue analysis method provides quickly and safely durability assement with the parametric workings on design model during pre-design phase.